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  • 1.
    Rittiruam, Meena
    et al.
    Chulalongkorn Univ, Thailand.
    Khamloet, Pisit
    Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand.
    Atthapak, Chayanon
    Chulalongkorn Univ, Thailand.
    Saelee, Tinnakorn
    Chulalongkorn Univ, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand.
    Screening of Cu-Mn-Ni-Zn high-entropy alloy catalysts for CO2 reduction reaction by machine-learning-accelerated density functional theory2024Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 652, artikel-id 159297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-entropy-alloy (HEA) catalysts have been used in many challenging electrocatalytic reactions, e.g., CO2 reduction reaction (CO2RR) due to their promising properties. For CO2RR catalysts, tuning metal compositions in Cu-based catalysts is one of the techniques to control the desired products. Thus, this work investigated the optimal composition of Cu-Mn-Ni-Zn HEA catalysts using high-throughput screening (HTS) for CO2RR targeting on two competing routes toward CH4 and CH3OH products. The screening protocol evaluates catalytic activity through adsorption energy (Eads) of *CO2, *CO, *COOH, and *H. At the same time, the selectivity is represented by Eads of *COH, *CH4, *CHO, and *CH3OH, using density functional theory (DFT) accelerated by machine learning techniques. The screening result from 11,920 data revealed 259 candidates for CH4-selective and 4,214 for CH3OH-selective catalysts. Interestingly, the Cu-Mn-Ni-Zn excellently prevented competitive hydrogen evolution reaction by up to 90%. Optimal composition for each route are Cu0.1Mn0.4Ni0.2Zn0.3 and Cu0.2Mn0.4- Ni0.1Zn0.3 in CH4-selective route and Cu0.3Mn0.3Ni0.2Zn0.2, Cu0.3Mn0.2Ni0.3Zn0.2, Cu0.3Mn0.2Ni0.2Zn0.3, and Cu0.2Mn0.3Ni0.3Zn0.2 in CH3OH-selective route. The optimal catalyst structure with high CO2RR activity in both routes was revealed to have the Mn atom as an active site, while Cu, Ni, and Zn as neighboring atoms. Hence, the Cu-Mn-Ni-Zn HEA catalyst is the promising electrocatalyst for CO2RR.

  • 2.
    Rittiruam, Meena
    et al.
    Chulalongkorn Univ, Thailand.
    Aumnongpho, Nuttanon
    Chulalongkorn Univ, Thailand.
    Saelee, Tinnakorn
    Chulalongkorn Univ, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand.
    Kheawhom, Soorathep
    Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand.
    The role of metal-doping on the enhanced electrocatalytic properties of a-MnO2 during oxygen reduction reaction2024Ingår i: Journal of Energy Storage, ISSN 2352-152X, E-ISSN 2352-1538, Vol. 78, artikel-id 110005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metal-doping is a common strategy for improving the performance of alpha-MnO2 during oxygen reduction reaction (ORR) in metal-air batteries (MABs). Understanding the role of dopants in an atomic level is crucial to develop this cathode's performance, which is required to study. This work presents the insight effects of metal-doping (Co, Ni, and Pd) in alpha-MnO2 during ORR, investigated through density functional theory and computational hydrogen electrode calculations. As a result, all dopants enhance the adsorption strength of surface species during ORR due to the induction of electron accumulation at the Mn site, modifying the d-band center of the doping site. Unfortunately, Ni doping had an inhibiting effect on specific ORR elementary steps, leading to lower activity. In the volcano plot of theoretical overpotential, Co and Pd doping play as the promoter, where enhanced ORR activity is found on the Mn-site. The insight information reveals that the enhanced alpha-MnO2 catalysts are achieved by Co and Pd doping at interstitial sites rather than substitution on Mn sites. These findings emphasize the critical role of both well-controlled dopant concentration and the atomic dispersion of a dopant at the interstitial sites on the electrocatalytic activity for MABs.

    Publikationen är tillgänglig i fulltext från 2025-12-12 15:31
  • 3.
    Ektarawong, A.
    et al.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand; Chulalongkorn Univ, Thailand.
    Johansson, E.
    Thermo Calc Software AB, Sweden.
    Pakornchote, T.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand; Chulalongkorn Univ, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Boron vacancy-driven thermodynamic stabilization and improved mechanical properties of AlB2-type tantalum diborides as revealed by first-principles calculations2023Ingår i: Journal of Physics: Materials, E-ISSN 2515-7639, Vol. 6, nr 2, artikel-id 025002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thermodynamic stability as well as structural, electronic, and elastic properties of boron-deficient AlB2-type tantalum diborides, which is designated as alpha-TaB2-x, due to the presence of vacancies at its boron sublattice are studied via first-principles calculations. The results reveal that alpha-TaB2-x, where 0.167 less than or similar to x less than or similar to 0.25, is thermodynamically stable even at absolute zero. On the other hand, the shear and Youngs moduli as well as the hardness of stable alpha-TaB2-x are predicted to be superior as compared to those of alpha-TaB2. The changes in the relative stability and also the elastic properties of alpha-TaB2-x with respect to those of alpha-TaB2 can be explained by the competitive effect between the decrease in the number of electrons filling in the antibonding states of alpha-TaB2 and the increase in the number of broken bonds around the vacancies, both induced by the increase in the concentration of boron vacancies. A good agreement between our calculated lattice parameters, elastic moduli and hardness of alpha-TaB2-x and the experimentally measured data of as-synthesized AlB2-type tantalum diborides with the claimed composition of TaB similar to 2, available in the literature, suggests that, instead of being a line compound with a stoichiometric composition of TaB2, AlB2-type tantalum diboride is readily boron-deficient, and its stable composition in equilibrium may be ranging at least from TaB similar to 1.833 to TaB similar to 1.75. Furthermore, the substitution of vacancies for boron atoms in alpha-TaB2 is responsible for destabilization of WB2-type tantalum diboride and orthorhombic Ta2B3, predicted in the previous theoretical studies to be thermodynamically stable in the Ta-B system, and it thus enables the interpretation of why the two compounds have never been realized in actual experiments.

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  • 4.
    Casillas-Trujillo, Luis
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten. Uppsala Univ, Sweden.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Effect of magnetic disorder on Cr interaction with 1/2 < 111 > screw dislocations in bcc iron2023Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 133, nr 12, artikel-id 125103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate how the magnetic state influences the interaction of Cr substitutional impurities with 1/2?111? screw dislocations in bcc Fe via density functional theory (DFT). We compare the paramagnetic state, modeled with a non-collinear disordered local moment (DLM) model, with the ferromagnetic state. In a previous work [Casillas-Trujillo et al., Phys. Rev. B 102, 094420 (2020)], we have shown that the magnetic moment and atomic volume landscape around screw dislocations in the paramagnetic state of iron are substantially different from that in the ferromagnetic state. Such a difference can have an impact in the formation energies of substitutional impurities, in particular, magnetic solutes. We investigate the formation energies of Cr solutes as a function of position with respect to the screw dislocation core, the interaction of Cr atoms along the dislocation line, and the segregation profile of Cr with respect to the dislocation in paramagnetic and ferromagnetic bcc iron. Our results suggest that with increasing temperature and connected entropic effects, Cr atoms gradually increase their occupation of dislocation sites, close to twice the amount of Cr in the DLM case than in the ferromagnetic case, with possible relevance to understand mechanical properties at elevated temperatures in low-Cr ferritic steels in use as structural materials in nuclear energy applications.

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  • 5.
    Rittiruam, Meena
    et al.
    Chulalongkorn Univ, Thailand.
    Khamloet, Pisit
    Chulalongkorn Univ, Thailand.
    Tantitumrongwut, Potipak
    Chulalongkorn Univ, Thailand.
    Saelee, Tinnakorn
    Chulalongkorn Univ, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand.
    Noppakhun, Jakapob
    Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand.
    First-Principles Active-Site Model Design for High-Entropy-Alloy Catalyst Screening: The Impact of Host Element Selection on Catalytic Properties2023Ingår i: Advanced Theory and Simulations, E-ISSN 2513-0390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Active-site models comprise miniature active sites on the host element, providing one of effective descriptors for screening high-entropy-alloy (HEA) catalysts using machine learning. This study investigates the impact of host elements on the electronic properties of active sites via density functional theory (DFT), where the active-site model is used in the HEA electrocatalysts. Also, the appropriate host element selection significantly affects the systems surface structures, electronic, and catalytic properties that adsorbate adsorption energy, d-band center, Bader charge, Zero-point energy, and entropy are used as accuracy verification parameters compared to the original surface. Ultimately, the novel guideline for active-site model construction is proposed using the simple example of PtPdFeCoNi high-entropy alloys. This investigation demonstrates that the host element selection is a crucial parameter to the active-site models, influencing the electronic structure and electrocatalytic properties.

  • 6.
    Mopoung, Kunpot
    et al.
    Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Bovornratanaraks, Thiti
    Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    First-principles demonstration of band filling-induced significant improvement in thermodynamic stability and mechanical properties of Sc1-xTaXB2 solid solutions2023Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 13, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mixtures of different metal diborides in the form of solid solutions are promising materials for hard-coating applications. Herein, we study the mixing thermodynamics and the mechanical properties of AlB2-structured Sc1-xTaXB2 solid solutions using the first-principles method, based on the density functional theory, and the cluster-expansion formalism. Our thermodynamic investigation reveals that the two diborides readily mix with one another to form a continuous series of stable solid solutions in the pseudo-binary TaB2 -ScB2 system even at absolute zero. Interestingly, the elastic moduli as well as the hardness of the solid solutions show significant positive deviations from the linear Vegards rule evaluated between those of ScB2 and TaB2. In case of Sc1-xTaXB2, the degrees of deviation from such linear trends can be as large as 25, 20, and 40% for the shear modulus, the Youngs modulus, and the hardness, respectively. The improvement in the stability as well as the mechanical properties of Sc1-xTaXB2 solid solutions relative to their constituent compounds is found to be related to the effect of electronic band filling, induced upon mixing TaB2 with ScB2. These findings not only demonstrate the prominent role of band filling in enhancing the stability and the mechanical properties of Sc1-xTaXB2, but also it can potentially open up a possibility for designing stable/metastable metal diboride-based solid solutions with superior and widely tunable mechanical properties for hard-coating applications.

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  • 7.
    Rittiruam, Meena
    et al.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Setasuban, Sorawee
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Noppakhun, Jakapob
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Saelee, Tinnakorn
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Aumnongpho, Nuttanon
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Boonchuay, Suphawich
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand.
    First-Principles Density Functional Theory and Machine Learning Technique for the Prediction of Water Adsorption Site on PtPd-Based High-Entropy-Alloy Catalysts2023Ingår i: Advanced Theory and Simulations, E-ISSN 2513-0390, Vol. 6, nr 4, artikel-id 2200926Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The water-gas shift reaction (WGSR) is employed in industry to obtain high-purity H-2 from syngas, where H2O adsorption is an important step that controls H2O dissociation in WGSR. Therefore, exploring catalysts exhibiting strong H2O adsorption energy (E-ads) is crucial. Also, high-entropy alloys (HEA) are promising materials utilized as catalysts, including in WGSR. The PtPd-based HEA catalysts are explored via density functional theory (DFT) and Gaussian process regression. The input features are based on the microstructure data and electronic properties: d-band center (epsilon(d)) and Bader net atomic charge (delta). The DFT calculation reveals that the epsilon(d) and delta of each active site of all HEA surfaces are broadly scattered, indicating that the electronic properties of each atom on HEA are non-uniform and influenced by neighboring atoms. The strong H2O-active-site interaction determined by a highly negative E-ads is used as a criterion to explore good PtPd-based WGSR catalyst candidates. As a result, the potential candidates are found to have Co, Ru, and Fe as an H2O adsorption site with Ag as a neighboring atom, that is, PtPdRhAgCo, PtPdRuAgCo, PtPdRhAgFe, and PtPdRuAgFe.

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  • 8.
    Ehn, Amanda
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    First-principles theory of the pressure-induced invar effect in FeNi alloys2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, nr 10, artikel-id 104422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Fe0.64Ni0.36 alloy exhibits an anomalously low thermal expansion at ambient conditions, an effect that is known as the invar effect. Other FexNi1-x alloys do not exhibit this effect at ambient conditions but upon application of pressure even Ni-rich compositions show low thermal expansion, thus called the pressure induced invar effect. We investigate the pressure induced invar effect for FexNi1-x for x = 0.64, 0.50, 0.25 by performing a large set of supercell calculations, taking into account noncollinear magnetic states. We observe anomalies in the equation of states for the three compositions. The anomalies coincide with magnetic transitions from a ferromagnetic state at high volumes to a complex magnetic state at lower volumes. Our results can be interpreted in the model of noncollinear magnetism which relates the invar effect to increasing contribution of magnetic entropy with pressure.

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  • 9.
    Wangphon, Chanthip
    et al.
    Chulalongkorn Univ, Thailand.
    Saelee, Tinnakorn
    Chulalongkorn Univ, Thailand.
    Rittiruam, Meena
    Chulalongkorn Univ, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand.
    How Can the PtPd-Based High-Entropy Alloy Triumphs Conventional Twc Catalyst During the NO Reduction? A Density Functional Theory Study2023Ingår i: Advanced Theory and Simulations, E-ISSN 2513-0390Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory is used to compare the catalytic performance of PtPdRhFeCo(100) high entropy alloy (HEA) three-way catalyst (TWC) to the conventional Pt(100) in the NO reduction step during NH3 production that supplies to passive NH3-SCR. Stronger adsorption of NO on the HEA(100) surface is beneficial to capture NO. During adsorption, the catalyst surface acts as an electron donor while the adsorbate is the acceptor on both HEA(100) and Pt(100) systems. Herein, the reaction mechanism of NO reduction can be classified into two steps: 1) NO activation and 2) product formation. During NO activation, direct NO dissociation is the preferable pathway on both HEA(100) and Pt(100) surfaces with the same Ea, whereas HNO and NOH pathways on HEA(100) are suppressed. For NH3, N2, and N2O production on HEA(100) is found to be more difficult than on Pt(100). However, the thermodynamic driving force of all reactions on HEA(100) is more spontaneous than on Pt(100). Also, the rate-determining step on HEA(100) is found to be NH3 formation different from the Pt(100), while difficult H diffusion on HEA(100) is the key factor that reduces NH3 production.

  • 10.
    Saelee, Tinnakorn
    et al.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Rittiruam Res Grp, Thailand.
    Boonchuay, Suphawich
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Sriwattana, Attachai
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Rittiruam, Meena
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Rittiruam Res Grp, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Khajondetchairit Res Grp, Thailand.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand.
    On the enhanced performance of Pt-based high-entropy alloys catalyst during water-gas shift reaction: A density functional theory study2023Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 623, artikel-id 157023Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electricity production from clean energy sources has gained attention during these decades. However, many power plants worldwide still use coal and natural gas as raw materials, which generates toxic gases, especially CO and CO2. To deal with this problem, transforming generated CO into another useful precursor before sup-plying it to the chemical process is a good idea. One of the most effective approaches is WGSR using a highly effective catalyst. In this work, we elucidate the insight information of PtPdRhFeCo HEA(1 1 1) surface improving the catalytic efficiency of Pt(1 1 1) surface. Interestingly, the homogenous form of electron distribution along Pt (1 1 1) surface is changed to heterogeneous forms creating unique electronic properties in which the electron donor and acceptor species exist simultaneously. The weakening interaction of CO corresponding to the strengthening interaction of CO2 on HEA(1 1 1) surface are advantages to preventing CO poison and trapping the CO2 after the WGSR. Moreover, the HEA(1 1 1) surface can thermodynamically promote the dissociation of H2O in pre-WGSR, creating active species of H*, O*, and OH* supplying to further the WGSR process. Nevertheless, consideration of PES along WGSR demonstrates that all possible pathways, including carboxyl, redox, and formate pathways along HEA(1 1 1) surface, are significantly improved by enhancing the thermodynamic driving force producing CO2.

  • 11.
    Gangaprasad Rao, Smita
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Mukhamedov, Boburjon
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Nagy, Gyula
    Uppsala Univ, Sweden.
    Tseng, Eric Nestor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Shu, Rui
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Boyd, Robert
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och ytbeläggningsfysik. Linköpings universitet, Medicinska fakulteten.
    Primetzhofer, Daniel
    Uppsala Univ, Sweden.
    Persson, Per O A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Le Febvrier, Arnaud
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Phase formation in CrFeCoNi nitride thin films2023Ingår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 7, nr 4, artikel-id 055002Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As a single-phase alloy, CrFeCoNi is a face centered cubic (fcc) material related to the archetypical highentropy Cantor alloy CrFeCoNiMn. For thin films, CrFeCoNi of approximately equimolar composition tends to assume an fcc structure when grown at room temperature by magnetron sputtering. However, the single-phase solid solution state is typically not achieved for thin films grown at higher temperatures. The same holds true for Cantor alloy-based ceramics (nitrides and oxides), where phase formation is extremely sensitive to process parameters such as the amount of reactive gas. This study combines theoretical and experimental methods to understand the phase formation in nitrogen-containing CrFeCoNi thin films. Density functional theory calculations considering three competing phases (CrN, Fe-Ni and Co) show that the free energy of mixing, Delta G of (CrFeCoNi)(1-x)N-x solid solutions has a maximum at x = 0.20-0.25, and AG becomes lower when x &lt; 0.20 and x &gt; 0.25. Thin films of (CrFeCoNi)1-xNx (0.14 &gt;= x &lt;= 0.41) grown by magnetron sputtering show stabilization of the metallic fcc when x &lt;= 0.22 and the stabilization of the NaCl B1 structure when x &gt; 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films and are of importance for understanding the phase-formation mechanisms in multicomponent ceramics. The results from the study further aid in making correlations between the observed mechanical properties and the crystal structure of the films.

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  • 12.
    Gambino, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Imperial Coll London, England.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Phase stability of Fe from first principles: Atomistic spin dynamics coupled with ab initio molecular dynamics simulations and thermodynamic integration2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, nr 1, artikel-id 014102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The calculation of free energies from first principles enables the prediction of phase stability of materials with high accuracy; these calculations are complicated in magnetic materials by the interplay of electronic, magnetic, and vibrational degrees of freedom. In this work, we show the feasibility and accuracy of the calculation of phase stability in magnetic systems with ab initio methods and thermodynamic integration by sampling the magnetic and vibrational phase space with coupled atomistic spin dynamics-ab initio molecular dynamics simulations [Stockem et al., PRL 121, 125902 (2018)], where energies and interatomic forces are calculated with density functional theory. We employ the method to calculate the phase stability of Fe at ambient pressure from 800 up to 1800 K. The Gibbs free energy difference between fcc and bcc Fe at zero pressure is calculated with thermodynamic integration over temperature and over stress-strain variables and, for the best set of exchange interactions employed, the Gibbs free energy difference between the two structures is within 5 meV/atom from the CALPHAD estimate, corresponding to an error in transition temperature below 150 K. The present work paves the way to free energy calculations in magnetic materials from first principles with accuracy in the order of 1 meV/atom.

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  • 13.
    Gambino, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Malyi, Oleksandr I.
    Univ Colorado, CO 80309 USA.
    Wang, Zhi
    Univ Colorado, CO 80309 USA; Chinese Acad Sci, Peoples R China.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Zunger, Alex
    Univ Colorado, CO 80309 USA.
    Density functional description of spin, lattice, and spin-lattice dynamics in antiferromagnetic and paramagnetic phases at finite temperatures2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 13, artikel-id 134406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Describing the (a) electronic and magnetic properties (EMPs) of compounds generally requires the specification of (b) the type of spin configurations one is considering [e.g., antiferromagnetic (AFM) or paramagnetic (PM) phases, with or without spin short-range order (SRO)] and lattice structure (e.g., atomic displacements, possible symmetry breaking) of such phases at a given temperature. Indeed, studying the interplay between the spin configuration and lattice structure (SCLS) and the ensuing EMPs has been an outstanding challenge in the theory of matter. The traditional approach of electronic phases of matter has generally focused on the interelectronic interactions, regarding the lattice structure as a spectator degree of freedom (DOF), often fixed from an external source (experiment or model assumptions). However, one expects that the EMPs of a compound can generally respond self-consistently to changes in SCLS (including symmetry), and at the same time, the SCLS can change in response to different electron and spin distributions visited during the calculation of the EMPs. This ping-pong-like interplay where structure affects electronic properties and the latter affect structure is indeed a cornerstone of much of the intricacy of understanding quantum materials. However, there is a limited understanding of the theory required to determine the SCLS at finite temperature in a way that can affect the EMPs and vice versa. We use here a practical, density functional theory (DFT)-based approach that provides the SCLS as a function of temperature, involving the description of spin, lattice, and spin-lattice dynamics of AFM and PM phases, thus providing the required ping-pong partners to the description of the EMPs of different phases. We distinguish three levels of dynamics: (I) dynamics of the spin DOFs treated via noncollinear Heisenberg Monte Carlo solved with exchange energies obtained from first-principles DFT cluster expansion, (II) dynamics of the lattice DOFs treated by ab initio molecular dynamics (AIMD) employing a fixed, representative spin configuration from Level I at the simulated temperature, and (III) coupling of spin and lattice dynamics via Landau-Lifshitz-Gilbert spin dynamics combined with AIMD. Such SCLSs at each of the three levels are used as inputs to DFT supercell calculations, providing the EMPs at each temperature. The results of this sequence include electronic band structures, bandgaps, density of states, as well as the statistical distribution of local moments and the SRO parameters, each as a function of temperature. Herein, we define a path to include temperature in magnetic insulators at different levels of spin dynamics by intercommunication between electronic structure theory and statistical mechanics. Using NiO as a test case, we address the separability of the DOFs in magnetic insulators for a minimal description of EMPs, demonstrating that inclusion of spin dynamics and, to some level, lattice dynamics is enough to explain the EMPs.

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  • 14.
    Mopoung, K.
    et al.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Ektarawong, A.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Pakornchote, T.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Johansson, E.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Effect of chemical composition and atomic configuration on thermodynamic stability and elastic properties of AlB2-type Sc1-XVXB2 solid solutions: A first-principles investigation2022Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 213, artikel-id 111616Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As a promising candidate for hard coating, the thermodynamic stability as well as the elastic properties, of ScB2-VB2 mixtures exhibiting the AlB2-type structure are examined using a combination of the cluster-expansion method and the first-principles calculations. Our prediction reveals that, upon cooling the mixtures to low temperatures, Sc and V atoms displays a strong preference for being surrounded by atoms of the opposite type, which reside in the second coordination shell of the metal sublattice. Such a configurational preference indicates a feasibility to fabricate Sc1-XVXB2 in the form of superlattices, as described by periodic arrangements of ScB2 and VB2 layers of different thickness along the &lt;0001&gt; direction. Interestingly, the stiffness, shear strength, and hardness of Sc1-XVXB2, where 0.375 &lt; X &lt; 0.625, in the form either of superlattice structures or of random solid solutions show significant positive deviations from the linear Vegards law, which can be understood in terms of the electronic band filling of the bonding states of Sc1-XVXB2. These findings also reveal that the elastic moduli and hardness of Sc1-XVXB2 are governed by the contents of ScB2 and VB2 constituting the mixtures, rather than by the atomic configuration of Sc and V.

    Publikationen är tillgänglig i fulltext från 2024-07-02 14:18
  • 15.
    Rittiruam, Meena
    et al.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Buapin, Puwit
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Saelee, Tinnakorn
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Khajondetchairit, Patcharaporn
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Kheawhom, Soorathep
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Praserthdam, Supareak
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    Praserthdam, Piyasan
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand.
    First-principles calculation on effects of oxygen vacancy on alpha-MnO2 and beta-MnO2 during oxygen reduction reaction for rechargeable metal-air batteries2022Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 926, artikel-id 166929Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    MnO2 is widely applied as oxygen reduction reaction (ORR) electrocatalysts in different metal-air batteries (MABs). Enhancing the ORR activity of MnO2 -based catalysts is necessary for improving the performance of MABs. Defect-engineering of catalyst materials is a key approach for enabling the high performance of ORR. Here, the defect-engineering of alpha-MnO2 (211) and beta-MnO2 (110) by oxygen vacancy (O-v) is investigated using the first-principles density functional theory calculation. The geometric structure, adsorption, electronic conductivity, and oxygen reduction reaction (ORR) activity are studied. As a result, the O-v induces the geometric structure that the Mn-Mn and Mn-O distances are closer when the catalysts lose the oxygen atom(s) on the top-layer surfaces. The presence of O-v not only enhances the adsorption energy of *OOH, *O, and *OH, but also increases the electronic conductivity analyzed via the electron transfer. The Bader charge analysis demonstrates that the Mn(IV) can be altered to Mn(III) by the electron accumulation from O-v. The volcano plot of ORR overpotential indicates that having the excess O-v concentration on MnO2 surfaces cannot enhance the ORR activity. The excellent activity is yielded by 12.50 % O-v alpha-(211) and 66.66 % O-v beta-(110) with the ORR overpotential of 0.31 V and 0.60 V, respectively. The results demonstrate that Ov is an essential parameter defining the existence of Mn(III) and Mn(IV) on the surface of MnO2-based catalysts. The optimal ratio of Mn(IV):Mn(III) is in challenge developing the alpha-MnO2 and beta-MnO2 electrocatalyst cathode for metal-air batteries. This study provides a guideline for developing the potential cathode catalyst for MABs, used for harvesting energy. (C) 2022 Elsevier B.V. All rights reserved.

  • 16.
    Leijon, Freddy
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Hydro Extruded Solut AB, Sweden.
    Johansson, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Hydro Extruded Solut AB, Sweden.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Skjervold, Svein
    Hydro Extruded Solut AB, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Investigation of Ti-1_x(Zr,Ta,V,W)(x)B-2 and A(l3)Ti(1_x)(Zr,V)(x) grain refiners in additively manufactured Al-2 wt%Cu alloys by a high throughput method2022Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 222, artikel-id 111093Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Grain refinement plays a central role in powder bed fusion (PBF) additive manufacturing by preventing hot cracking and thus enabling the development of high-strength alloys. However, the mechanism behind grain refinement is not fully understood for conventional casting, nor for PBF. In this work, a high throughput method have been used to produce Al-2 wt%Cu alloys with additions of Ti1-xM(Zr,Ta,V,W)(x)B-2, Al3Ti1-xM(Zr,V)(x) or AlB2 grain refiners for 0.1 &lt; x &lt; 0.9. It was found that grain size varied with x, M and the sum of Ti + M. Ti1-xMxB2 grain refiners offered no advantage over Al3Ti1-xMx. Overall, Ti and Zr provide the best grain refinement, both as Ti1-xMxB2 and Al3Ti1-xMx. However, Ti1-xZrxB2 had a grain refinement minimum around x = 0.65-0.70. The behavior was similar with Ta, but to a lesser extent. V and W had detrimental effects on grain refinement. Despite the fact that no AlB2 particles were observed, additions of B provided excellent grain refinement and was more efficient than Ti below 0.5at%. Ti1-xMxB2 lattice parameters varied with x and followed Vegards law, however, a clear relationship between grain size and epitaxial strain/lattice match could not be established. Similarly, the growth restricting factor alone was not a predictor of grain size.

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  • 17.
    Brännvall, Marian
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Gambino, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Machine learning approach for longitudinal spin fluctuation effects in bcc Fe at Tc and under Earth-core conditions2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 14, artikel-id 144417Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a machine learning approach to predict the shapes of the longitudinal spin fluctuation (LSF) energy landscapes for each local magnetic moment. This approach allows the inclusion of the effects of LSFs in, e.g., the simulation of a magnetic material with ab initio molecular dynamics in an effective way. This type of simulation requires knowledge of the reciprocal interaction between atoms and moments, which, in principle, would entail calculating the energy landscape of each atom at every instant in time. The machine learning approach is based on the kernel ridge regression method and developed using bcc Fe at the Curie temperature and ambient pressure as a test case. We apply the trained machine learning models in a combined atomistic spin dynamics and ab initio molecular dynamics (ASD-AIMD) simulation, where they are used to determine the sizes of the magnetic moments of every atom at each time step. In addition to running an ASD-AIMD simulation with the LSF machine learning approach for bcc Fe at the Curie temperature, we also simulate Fe at temperature and pressure comparable to the conditions at the Earth's inner solid core. The latter simulation serves as a critical test of the generality of the method and demonstrates the importance of the magnetic effects in Fe in the Earth's core despite its extreme temperature and pressure.

  • 18.
    Bykova, Elena
    et al.
    Carnegie Inst Sci, DC 20015 USA; Univ Bayreuth, Germany.
    Johansson, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bykov, Maxim
    Carnegie Inst Sci, DC 20015 USA; Univ Cologne, Germany.
    Chariton, Stella
    Univ Chicago, IL 60637 USA.
    Fei, Hongzhan
    Univ Bayreuth, Germany.
    Ovsyannikov, Sergey V.
    Univ Bayreuth, Germany.
    Aslandukova, Alena
    Univ Bayreuth, Germany.
    Gabel, Stefan
    Friedrich Alexander Univ Erlangen Nurnberg, Germany.
    Holz, Hendrik
    Friedrich Alexander Univ Erlangen Nurnberg, Germany; Univ Kassel, Germany.
    Merle, Benoit
    Friedrich Alexander Univ Erlangen Nurnberg, Germany; Univ Kassel, Germany.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Abrikosov, Igor A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Smith, Jesse S.
    Argonne Natl Lab, IL 60439 USA.
    Prakapenka, Vitali B.
    Univ Chicago, IL 60637 USA.
    Katsura, Tomoo
    Univ Bayreuth, Germany.
    Doubrovinckaia, Natalia
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Bayreuth, Germany.
    Goncharov, Alexander F.
    Carnegie Inst Sci, DC 20015 USA.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Novel Class of Rhenium Borides Based on Hexagonal Boron Networks Interconnected by Short B-2 Dumbbells2022Ingår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 34, nr 18, s. 8138-8152Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transition metal borides are known due to their attractive mechanical, electronic, refractive, and other properties. A new class of rhenium borides was identified by synchrotron single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells between 26 and 75 GPa. Recoverable to ambient conditions, compounds rhenium triboride (ReB3) and rhenium tetraboride (ReB4) consist of close-packed single layers of rhenium atoms alternating with boron networks built from puckered hexagonal layers, which link short bonded (similar to 1.7 angstrom) axially oriented B-2 dumbbells. The short and incompressible Re-B and B-B bonds oriented along the hexagonal c-axis contribute to low axial compressibility comparable with the linear compressibility of diamond. Sub-millimeter samples of ReB3 and ReB4 were synthesized in a large-volume press at pressures as low as 33 GPa and used for material characterization. Crystals of both compounds are metallic and hard (Vickers hardness, H-V = 34(3) GPa). Geometrical, crystal-chemical, and theoretical analysis considerations suggest that potential ReBx compounds with x &gt; 4 can be based on the same principle of structural organization as in ReB3 and ReB4 and possess similar mechanical and electronic properties.

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  • 19.
    Kanchanavatee, N.
    et al.
    Chulalongkorn Univ, Thailand.
    Ektarawong, A.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand; Chulalongkorn Univ, Thailand.
    Pakornchote, T.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hodak, S.
    Chulalongkorn Univ, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Phase transitions and suppression of magnetoresistance in WTe2-xSex system2022Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 34, nr 43, artikel-id 435403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray diffraction, Raman spectroscopy, and electrical resistivity measurements on polycrystalline WTe2-xSex (0 &lt;= x &lt;= 0.8) reveal a T-d - 1T structural phase transition and suppression of magnetoresistance at x = 0.2. These phenomena are consistent with the pressure phase diagram of WTe2. However, chemical pressure due to substitution of smaller Se ion cannot generate pressure required for the phase transition. Strain induced by sample inhomogeneity is believed to be a trigger to the behaviors. In agreement with previous predictions and reports, a mixed phase of 1T and 2H structures was also detected in Se-rich samples. Coincidentally at x = 0.2, electrical resistivity analysis suggests a phase transition from a metallic phase to a nonmetallic phase that is possibly a topological-insulating phase.

  • 20.
    Le Febvrier, Arnaud
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Gambino, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Giovannelli, Fabien
    Univ Tours, France.
    Bakhit, Babak
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hurand, Simon
    Univ Poitiers, France.
    Abadias, Gregory
    Univ Poitiers, France.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    p-type behavior of CrN thin films via control of point defects2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 10, artikel-id 104108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the results of a combined experimental and theoretical study on nonstoichiometric CrN1+δ thinfilms grown by reactive magnetron sputtering on c-plane sapphire and MgO (100) substrates in an Ar/N2 gasmixture using different percentages of N2. There is a transition from n-type to p-type behavior in the layersas a function of nitrogen concentration varying from 48 to 52 at. % in CrN films. The compositional changefollows a similar trend for all substrates, with a N/Cr ratio increasing from approximately 0.7 to 1.06–1.11 byincreasing the percentage of N2 in the gas flow ratio. As a result of the change in stoichiometry, the latticeparameter and the Seebeck coefficient increase together with the increase of N in CrN1+δ ; in particular, theSeebeck value coefficient transitions from –50 μV K–1 for CrN0.97 to +75μV K–1 for CrN1.1. Density functionaltheory calculations show that Cr vacancies can account for the change in the Seebeck coefficient, since they pushthe Fermi level down in the valence band, whereas N interstitial defects in the form of N2 dumbbells are neededto explain the increasing lattice parameter. Calculations including both types of defects, which have a strongtendency to bind together, reveal a slight increase in the lattice parameter and a simultaneous formation of holesin the valence band. To explain the experimental trends, we argue that both Cr vacancies and N2 dumbbells,possibly in combined configurations, are present in the films. We demonstrate the possibility of controlling thesemiconducting behavior of CrN with intrinsic defects from n to p type, opening possibilities to integrate thiscompound in energy-harvesting thermoelectric devices.

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  • 21.
    Mukhamedov, Boburjon
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Fritze, S.
    Uppsala Univ, Sweden.
    Ottosson, M.
    Uppsala Univ, Sweden.
    Osinger, B.
    Uppsala Univ, Sweden.
    Lewin, E.
    Uppsala Univ, Sweden.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Jansson, U.
    Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci & Technol MISIS, Russia.
    Tetragonal distortion in magnetron sputtered bcc-W films with supersaturated carbon2022Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 214, artikel-id 110422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon has a low solid solubility in bcc tungsten at equilibrium. However, metastable supersaturated solid solutions can be synthesized with magnetron sputtering. Here, we present a systematic study on the phase stability and mechanical properties of such supersaturated W-C solid solutions. H-2h scans show a split of the 200/020 and the 002 peaks for supersaturated films which is explained by a tetragonal distortion of the bcc structure. This split increases with increasing C content and is maximized at 4 at.% C, where we observe an a/b axis of 3.15-3.16 A and a c-axis of 3.21-3.22 A. We performed first-principles calculations of lattice parameters, mixing enthalpies, elastic constants and polycrystalline elastic moduli for cubic and tetragonal W-C solid solutions. Calculations show that tetragonal structure is more stable than the bcc supersaturated solid solution and the calculated lattice parameters and Youngs moduli follow the same trends as the experimental ones as a function of C concentration. The results suggest that supersaturated films with lattice distortion can be used as a design approach to improve the properties of transition metal films with a bcc structure. (c) 2022 The Authors. Published by Elsevier Ltd.

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  • 22.
    Johansson, Erik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Tasnadi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Rosén, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Materialdesign. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    The effect of strain and pressure on the electron-phonon coupling and superconductivity in MgB2-Benchmark of theoretical methodologies and outlook for nanostructure design2022Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 131, nr 6, artikel-id 063902Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different theoretical methodologies are employed to investigate the effect of hydrostatic pressure and anisotropic stress and strain on the superconducting transition temperature ( T-c) of MgB2. This is done both by studying Kohn anomalies in the phonon dispersions alone and by explicit calculation of the electron-phonon coupling. It is found that increasing pressure suppresses T-c in all cases, whereas isotropic and anisotropic strain enhances the superconductivity. In contrast to trialed epitaxial growth that is limited in the amount of achievable lattice strain, we propose a different path by co-deposition with ternary diborides that thermodynamically avoid mixing with MgB2. This is suggested to promote columnar growth that can introduce strain in all directions.

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  • 23.
    Tsuppayakorn-aek, P.
    et al.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Ektarawong, A.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Sukmas, W.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Thermodynamic stability and superconductivity of tantalum carbides from first-principles cluster expansion and isotropic Eliashberg theory2022Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 202, artikel-id 111004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phase stability of tantalum carbides, particularly cubic rocksalt TaCx and hexagonal Ta2Cx, where 0 ≤ x ≤ 1 due to the presence of vacancies on the C sites, is explored using a first-principles cluster-expansion method. Our results demonstrate that at 0 K, in addition to stoichiometric cubic TaC and hexagonal Ta2C both widely known in the literature, carbon-deficient face-centered orthorhombic TaC0.833 is identified as a thermodynamically stable phase in the binary Ta-C system. By investigating their vibrational and electronic properties, the three carbides are dynamically stable and are metallic. We further demonstrate, by adopting phonon mediated superconductivity based on the Bardeen-Cooper-Schrieffer theory, that cubic TaC, face-centered orthorhombic TaC0.833, and hexagonal Ta2C superconduct, whose transition temperatures are estimated by the Allen-Dynes equation to be 10.0 K, 6.8 K, and 1.4 K, respectively. The physical origin of superconductivity in these stable carbides are discussed and described, based on the detailed analysis of the materials electronic and phonon properties.

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  • 24.
    Ektarawong, A.
    et al.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand; Chulalongkorn Univ, Thailand.
    Khamkaeo, S.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    A comparison of the mixing thermodynamics of the antifluorite-structured Mg2Si1-xGex, Mg2Sn1-xGex and Mg2Si1-xSnx alloys from first principles2021Ingår i: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 185, artikel-id 110018Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mixing thermodynamics of the antifluorite-structured Mg2Si1-xGex is investigated using the first-principles calculations. We find that Mg2Si and Mg2Ge readily mix with each other leading to formation of a single-phase random solid solutions of Mg2Si1-xGex across the entire composition range from the temperature of about 50 K and above. At 0 K, Mg2Si1-xGex exhibits a weak energy preference toward local phase segregation into Mg2Si and Mg2Ge without forming any ordered patterns of Si and Ge atoms. Through a comparison with the mixing thermodynamics of Mg2Sn with Mg2Si or Mg2Ge, a small lattice misfit between Mg2Si and Mg2Ge of less than 1 % is responsible for the formation of stable Mg2Si1-xGex random solid solutions at such a low temperature. Besides their thermodynamic stability, our prediction reveals that the random solid solutions of Mg2Si1-xGex are dynamically and mechanically stable. These findings justify the uses of structural models of Mg2Si1-xGex, assuming a random distribution of Si and Ge atoms in the previous theoretical studies, and also provide an insight into the complete solubility of Mg2Ge in Mg2Si and vice versa at all temperature where the atomic diffusion is activated.

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  • 25.
    Johansson, Erik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Rosén, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Coupling of lattice dynamics and configurational disorder in metal deficient Al1-delta B2 from first-principles2021Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 130, nr 1, artikel-id 015110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the role metal vacancies play in the phase stability and properties of Al1-delta B2 using first-principles calculations, alloy theory simulations, phonon calculations, and experimental in situ x-ray diffraction measurements of thermal expansion. The relevant concentrations and configurations of metal vacancies are analyzed using cluster expansion and special quasirandom structure methods combined with vibrational free energy calculations within the quasiharmonic approximation for ordered and disordered phases. We find that electronic structure effects stabilize Al1-delta B2 in a narrow composition range of 0.073 &lt; delta &lt; 0.096 depending only weakly on temperature while they destabilize ideal stoichiometric AlB2. This composition corresponds to the narrow range 0:311 &lt;= x &lt;= 0.317 in the formulation of AlxB1-x, which can explain the appearance of this phase as a line compound with the ideal AlB2 stoichiometry in most phase diagrams. The ordered structures of vacancies found at low temperature are destabilized and disordered already at a low temperature of similar to 200 K. Our experiments observe linear thermal expansion coefficients alpha(a) = 4.8 x 10(-6) K-1 and alpha(c) = 10.85 x 10(-6) K-1 at room temperature. Only thermal expansion calculations of disordered phases compare well with these measurements, and, in particular, stoichiometric vacancy-free AlB2 shows dramatic overestimations of the experimental thermal expansion. These results highlight the importance of disordered Al vacancies on both stability and vibrational properties of Al1-delta B2. (c) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

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  • 26.
    Sukmas, W.
    et al.
    Extreme Conditions Physics Research Laboratory (ECPRL), Physics of Energy Materials Research Unit (PEMRU), Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand; Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 328 Si Ayutthaya Road, Bangkok, 10400, Thailand.
    Ektarawong, A.
    Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 328 Si Ayutthaya Road, Bangkok, 10400, Thailand; Chula Intelligent and Complex Systems (CHICS), Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
    Tsuppayakorn-Aek, P.
    Extreme Conditions Physics Research Laboratory (ECPRL), Physics of Energy Materials Research Unit (PEMRU), Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand; Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 328 Si Ayutthaya Road, Bangkok, 10400, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Pinsook, U.
    Extreme Conditions Physics Research Laboratory (ECPRL), Physics of Energy Materials Research Unit (PEMRU), Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand; Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 328 Si Ayutthaya Road, Bangkok, 10400, Thailand.
    Bovornratanaraks, T.
    Extreme Conditions Physics Research Laboratory (ECPRL), Physics of Energy Materials Research Unit (PEMRU), Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand; Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 328 Si Ayutthaya Road, Bangkok, 10400, Thailand.
    Data-driven analysis of the rotational energy landscapes of an organic cation in a substituted alloy perovskite2021Ingår i: Materials Advances, E-ISSN 2633-5409, Vol. 2, nr 7, s. 2366-2372Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lead-free hybrid organic-inorganic perovskites have recently emerged as excellent materials particularly in highly potential yet low-cost photovoltaic technologies. Calculations have previously suggested that CH3NH3BiSeI2 can be used as an alternative material for the highly studied CH3NH3PbI3 due to its eco-friendliness and comparable performance. Herein, with the aid of Euler angles, the interplay between the organic CH3NH3 (MA) cation and the inorganic BiSeI2 framework, obtained from first-principles calculations, is thoroughly scrutinised by means of the multidimensional total energy landscape. The highest peak of 17.9 meV per atom, protruding from the average plateau of 9 meV per atom within the four-dimensional topography, is equivalent to 208 K, the temperature at which the MA cations freely reorient. Moreover, the complexity of the angle-energy relationship is mitigated by exploiting a high-fidelity simulation based on deep learning. The deep artificial neural network of five hidden layers with 500 neurons, each fed by ten descriptors-three Euler angles and seven various bond lengths-predicts the total energies with an accuracy within the root mean square error of 0.39 ± 0.03 meV per atom for the test dataset. This novel statistical model in turn offers a tantalising promise to provide an accurate prediction of this materials energies, while diminishing the need for costly first-principles calculations. © The Royal Society of Chemistry.

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  • 27.
    Atthapak, C.
    et al.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Ektarawong, A.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Pakornchote, T.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Effect of atomic configuration and spin-orbit coupling on thermodynamic stability and electronic bandgap of monolayer 2H-Mo1-xWxS2 solid solutions2021Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 23, nr 24, s. 13535-13543Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Through a combination of density functional theory calculations and cluster-expansion formalism, the effect of the configuration of the transition metal atoms and spin-orbit coupling on the thermodynamic stability and electronic bandgap of monolayer 2H-Mo1-xWxS2 is investigated. Our investigation reveals that, in spite of exhibiting a weak ordering tendency of Mo and W atoms at 0 K, monolayer 2H-Mo1-xWxS2 is thermodynamically stable as a single-phase random solid solution across the entire composition range at temperatures higher than 45 K. The spin-orbit coupling effect, induced mainly by W atoms, is found to have a minimal impact on the mixing thermodynamics of Mo and W atoms in monolayer 2H-Mo1-xWxS2; however, it significantly induces change in the electronic bandgap of the monolayer solid solution. We find that the band-gap energies of ordered and disordered solid solutions of monolayer 2H-Mo1-xWxS2 do not follow Vegards law. In addition, the degree of the SOC-induced change in band-gap energy of monolayer 2H-Mo1-xWxS2 solid solutions not only depends on the Mo and W contents, but for a given alloy composition it is also affected by the configuration of the Mo and W atoms. This poses a challenge of fine-tuning the bandgap of monolayer 2H-Mo1-xWxS2 in practice just by varying the contents of Mo and W.

  • 28.
    Ektarawong, A.
    et al.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Tsuppayakorn-aek, P.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Kanchanavatee, N.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Effect of thermally excited lattice vibrations on the thermodynamic stability of tungsten ditellurides WTe2 under high pressure: A first-principles investigation2021Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 186, artikel-id 110024Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The thermodynamic stability as a function of pressure and temperature of three WTe2 polytypes, i. e., Td, 1T , and 2H phases, is examined using first-principles calculations, where the temperature-dependent contributions, arising particularly from the lattice vibrations, are derived from the quasiharmonic approximation. We find that the critical transition pressure to the 2H phase increases almost linearly with increasing temperature. Through the inspection of the phonon density of states, 2H-WTe2 is dynamically stable not only at high pressure, but also at zero pressure, indicating possible existence of 2H-WTe2 also at ambient conditions. On the other side, our results demonstrate that, at relevant temperature and pressure, the thermodynamic stability of 1T-WTe2 is comparable to that of Td-WTe2, and further analysis reveals substantial similarities in terms of structural behavior between Td-WTe2 and 1T-WTe2. These findings suggest not only that the two polytypes are likely to coexist in practical samples of WTe2 due probably to grains/regions either with tiny difference in stress, for example, or with different growth history, but also that the designation of 1T , having been regularly used to described the compound under pressure in the literature, might actually be a mixture of Td and 1T polytypes, whose WTe2 layers laterally slide via low transition barrier induced probably by the applied pressure, resulting in the splitting of (101) and (113) peaks as observed in the diffraction experiments.

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  • 29.
    Casillas Trujillo, Luis
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Osinger, Barbara
    Uppsala Univ, Sweden.
    Lindblad, Rebecka
    Uppsala Univ, Sweden.
    Karlsson, Dennis
    Uppsala Univ, Sweden.
    Abrikossov, Alexei
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Fritze, Stefan
    Uppsala Univ, Sweden.
    von Fieandt, Kristina
    Uppsala Univ, Sweden.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hotz, Ingrid
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Jansson, Ulf
    Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci & Technol MISIS, Russia.
    Lewin, Erik
    Uppsala Univ, Sweden.
    Experimental and theoretical evidence of charge transfer in multi-component alloys - how chemical interactions reduce atomic size mismatch2021Ingår i: Materials Chemistry Frontiers, E-ISSN 2052-1537, Vol. 5, nr 15, s. 5746-5759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio simulations of a multi-component alloy using density functional theory (DFT) were combined with experiments on thin films of the same material using X-ray photoelectron spectroscopy (XPS) to study the connection between the electronic and atomic structures of multi-component alloys. The DFT simulations were performed on an equimolar HfNbTiVZr multi-component alloy. Structure and charge transfer were evaluated using relaxed, non-relaxed, as well as elemental reference structures. The use of a fixed sphere size model allowed quantification of charge transfer, and separation into different contributions. The charge transfer was generally found to follow electronegativity trends and results in a reduced size mismatch between the elements, and thus causes a considerable reduction of the lattice distortions compared to a traditional assumption based on tabulated atomic radii. A calculation of the average deviation from the average radius (i.e. the so-called delta-parameter) based on the atomic Voronoi volumes gave a reduction of delta from ca. 6% (using the volumes in elemental reference phases) to ca. 2% (using the volumes in the relaxed multi-component alloy phase). The reliability of the theoretical results was confirmed by XPS measurements of a Hf22Nb19Ti18V19Zr21 thin film deposited by sputter deposition. The experimentally observed core level binding energy shifts (CLS), as well as peak broadening due to a range of chemical surroundings, for each element showed good agreement with the calculated DFT values. The single solid solution phase of the sample was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) including energy dispersive spectroscopy (EDS) with nm-resolution. These observations show that the HfNbTiVZr solid solution phase is non-ideal, and that chemical bonding plays an important part in the structure formation, and presumably also in the properties. Our conclusions should be transferable to other multi-component alloy systems, as well as some other multi-component material systems, and open up interesting possibilities for the design of material properties via the electronic structure and controlled charge transfer between selected metallic elements in the materials.

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  • 30.
    Gharavi, Mohammad Amin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Gambino, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Le Febvrier, Arnaud
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    High thermoelectric power factor of pure and vanadium-alloyed chromium nitride thin films2021Ingår i: Materials Today Communications, ISSN 2352-4928, Vol. 28, artikel-id 102493Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chromium-nitride based materials have shown unexpected promise as thermo-electric materials for, e.g., wasteheat harvesting. Here, CrN and (Cr,V)N thin films were deposited by reactive magnetron sputtering. Thermoelectric measurements of pure CrN thin films show a low electrical resistivity between 1.2 and 1.5 x 10(-3) Omega cm and very high values of the Seebeck coefficient and thermoelectric power factor, in the range between 370-430 mu V/K and 9-11 x 10(-3) W/mK(2), respectively. Alloying of CrN films with small amounts (less than 15 %) of vanadium results in cubic (Cr,V)N thin films. Vanadium decreases the electrical resistivity and yields powerfactor values in the same range as pure CrN. Density functional theory calculations of sub-stoichiometric CrN1-delta and (Cr,V)N1-delta show that nitrogen vacancies and vanadium substitution both cause n-type conductivity and features in the band structure typically correlated with a high Seebeck coefficient. The results suggest that slight variations in nitrogen and vanadium content affect the power factor and offers a means of tailoring the power factor and thermoelectric figure of merit.

  • 31.
    Casillas Trujillo, Luis
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Identification of materials with strong magnetostructural coupling using computational high-throughput screening2021Ingår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 5, nr 3, artikel-id 034417Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Important phenomena such as magnetostriction, magnetocaloric, and magnetoelectric effects arise from, or could be enhanced by, the coupling of magnetic and structural degrees of freedom. The coupling of spin and lattice also influence transport and structural properties in magnetic materials, in particular around phase transitions. In this paper we propose a method for screening materials for a strong magnetostructural coupling by assessing the effect of the local magnetic configuration on the atomic forces using density functional theory. We have employed the disordered local moment approach in a supercell formulation to probe different magnetic local configurations and their forces and performed a high-throughput search on binary and ternary compounds available in the Crystallography Open Database. We identify a list of materials with a strong spin-lattice coupling out of which several are already known to display magnetolattice coupling phenomena such as Fe3O4 and CrN. Others, such as Mn2CrO4 and CaFe7O11, have been less studied and have yet to reveal their potentials in experiments and applications.

  • 32.
    Zaleski, Karol
    et al.
    Adam Mickiewicz Univ, Poland.
    Ekholm, Marcus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci & Technol MISIS, Russia.
    Dubowik, Janusz
    Polish Acad Sci, Poland.
    Local atomic configuration approach to the nonmonotonic concentration dependence of magnetic properties of Ni(2)Mn(1+x)Z(1-x) (Z = In, Sn, Sb) Heusler alloys2021Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 194, artikel-id 113646Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Ni(2)Mn(1+x)Z(1-x) Heusler alloys, where Z = In, Sn, Sb are attractive candidates for shape memory applications. The effect is directly related to their magnetic properties. We have studied these systems by ab-initio calculations and experiments, focusing on magnetic moments and exchange-bias fields. The calculations indicate that the composition dependence of the total magnetic moment is due to competing ferro-magnetic and antiferromagnetic alignment between Mn atoms on different sublattices and with different local environments. This phenomenon can also explain the composition dependence of the exchange-bias effect. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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  • 33.
    Gharavi, Mohammad Amin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Le Febvrier, Arnaud
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Greczynski, Grzegorz
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Phase Transformation and Superstructure Formation in (Ti-0.5, Mg-0.5)N Thin Films through High-Temperature Annealing2021Ingår i: Coatings, ISSN 2079-6412, Vol. 11, nr 1, artikel-id 89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    (Ti-0.5, Mg-0.5)N thin films were synthesized by reactive dc magnetron sputtering from elemental targets onto c-cut sapphire substrates. Characterization by theta-2 theta X-ray diffraction and pole figure measurements shows a rock-salt cubic structure with (111)-oriented growth and a twin-domain structure. The films exhibit an electrical resistivity of 150 m omega center dot cm, as measured by four-point-probe, and a Seebeck coefficient of -25 mu V/K. It is shown that high temperature (similar to 800 degrees C) annealing in a nitrogen atmosphere leads to the formation of a cubic LiTiO2-type superstructure as seen by high-resolution scanning transmission electron microscopy. The corresponding phase formation is possibly influenced by oxygen contamination present in the as-deposited films resulting in a cubic superstructure. Density functional theory calculations utilizing the generalized gradient approximation (GGA) functionals show that the LiTiO2-type TiMgN2 structure has a 0.07 eV direct bandgap.

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  • 34.
    Gharavi, Mohammad Amin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Theoretical study of the phase transitions and electronic structure of (Zr-0.5, Mg-0.5)N and (Hf-0.5, Mg-0.5)N2021Ingår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 56, nr 1, s. 305-312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rock-salt scandium nitride has gained interest due to its thermoelectric properties including a relatively high Seebeck coefficient. This motivates research for other semiconductor materials that exhibit similar electronic structure features as ScN. Using density functional theory calculations, we have studied disordered solid solutions of (Zr-0.5, Mg-0.5)N and (Hf-0.5, Mg-0.5)N using the special quasi-random structure model. The results show that within a mean-field approximation for the configurational entropy, the order-disorder phase transformation between the monoclinic LiUN(2)prototype structure and the rock-salt cubic random alloy of these mentioned solid solutions occur at 740 K and 1005 K for (Zr-0.5, Mg-0.5)N and (Hf-0.5, Mg-0.5)N, respectively. The density-of-states for the two ternary compounds is also calculated and predicts semiconducting behavior with band gaps of 0.75 eV for (Zr-0.5, Mg-0.5)N and 0.92 eV for (Hf-0.5, Mg-0.5)N. The thermoelectric properties of both compounds are also predicted. We find that in the range of a moderate change in the Fermi level, a high Seebeck coefficient value at room temperature can be achieved.

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  • 35.
    Casillas Trujillo, Luis
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Configurational thermodynamics of a 1/2111 screw dislocation core in Mo-W solid solutions using cluster expansion2020Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 128, nr 4, artikel-id 045114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we have developed a methodology to obtain an ab initio cluster expansion of a system containing a dislocation and studied the effect of configurational disorder on the 1/2111 screw dislocation core structure in disordered Mo1-xWx alloys. Dislocation cores control the selection of glide planes, cross slip, and dislocation nucleation. Configurational disorders in alloys can impact the dislocation core structure and affect dislocation mobility. For our calculations, we have used a quadrupolar periodic array of screw dislocation dipoles and obtained the relaxed structures and energies using density functional theory. We have obtained the dislocation core structure as a function of composition and the interaction energies of solutes with the dislocation as a function of position with respect to the core. With these energies, we performed mean-field calculations to assess segregation toward the core. Finally, with the calculated energies of 1848 alloy configurations with different compositions, we performed a first principle cluster expansion of the configurational energetics of Mo1-xWx solid solutions containing dislocations.

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  • 36.
    Casillas Trujillo, Luis
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Jansson, Ulf
    Uppsala Univ, Sweden.
    Sahlberg, Martin
    Uppsala Univ, Sweden.
    Ek, Gustav
    Uppsala Univ, Sweden.
    Nygard, Magnus M.
    Inst Energy Technol, Norway.
    Sorby, Magnus H.
    Inst Energy Technol, Norway.
    Hauback, Bjorn C.
    Inst Energy Technol, Norway.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci & Technol MISIS, Russia.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Interstitial carbon in bcc HfNbTiVZr high-entropy alloy from first principles2020Ingår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 4, nr 12, artikel-id 123601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The remarkable mechanical properties of high-entropy alloys can be further improved by interstitial alloying. In this work we employ density functional theory calculations to study the solution energies of dilute carbon interstitial atoms in tetrahedral and octahedral sites in bcc HfNbTiVZr. Our results indicate that carbon interstitials in tetrahedral sites are unstable, and the preferred octahedral sites present a large spread in the energy of solution. The inclusion of carbon interstitials induces large structural relaxations with long-range effects. The effect of local chemical environment on the energy of solution is investigated by performing a local cluster expansion including studies of its correlation with the carbon atomic Voronoi volume. However, the spread in solution energetics cannot be explained with a local environment analysis only pointing towards a complex, long-range influence of interstitial carbon in this alloy.

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  • 37.
    Gambino, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Brännvall, Marian
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ehn, Amanda
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hedström, Ylva
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Longitudinal spin fluctuations in bcc and liquid Fe at high temperature and pressure calculated with a supercell approach2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 1, artikel-id 014402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Investigating magnetic materials at realistic conditions with first-principles methods is a challenging task due to the interplay of vibrational and magnetic degrees of freedom. The most difficult contribution to include in simulations is represented by the longitudinal magnetic degrees of freedom [longitudinal spin fluctuation (LSF)] due to their inherent many-body nature; nonetheless, schemes that enable to take into account this effect on a semiclassical level have been proposed and employed in the investigation of magnetic systems. However, assessment of the effect of vibrations on LSF is lacking in the literature. For this reason, in this work we develop a supercell approach within the framework of constrained density functional theory to calculate self-consistently the size of local-environment-dependent magnetic moments in the paramagnetic, high-temperature state in the presence of lattice vibrations and for liquid Fe in different conditions. First, we consider the case of bcc Fe at the Curie temperature and ambient pressure. Then, we perform a similar analysis on bcc Fe at Earths inner-core conditions, and we find that LSFs stabilize nonzero moments which affect atomic forces and the electronic density of states of the system. Finally, we employ the present scheme on liquid Fe at the melting point at ambient pressure and at Earths outer-core conditions (p approximate to 200 GPa, T approximate to 6000 K). In both cases, we obtain local magnetic moments of sizes comparable to the solid-state counterparts.

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  • 38.
    Ektarawong, A.
    et al.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res and Innovat, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res and Innovat, Thailand.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Role of spin-orbit coupling in the alloying behavior of multilayer Bi1-xSbx solid solutions revealed by a first-principles cluster expansion2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, nr 13, artikel-id 134104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We employ a first-principles cluster-expansion method in combination with canonical Monte Carlo simulations to study the effect of spin-orbit coupling on the alloying behavior of multilayer Bi1-xSbx. Our simulations reveal that spin-orbit coupling plays an essential role in determining the configurational thermodynamics of Bi and Sb atoms. Without the presence of spin-orbit coupling, Bi1-xSbx is predicted to exhibit at low-temperature chemical ordering of Bi and Sb atoms, leading to formation of an ordered structure at x approximate to 0.5. Interestingly, the spin-orbit-coupling effect intrinsically induced by the existence of Bi and Sb results in the disappearance of chemical ordering of the constituent elements within an immiscible region existing at T &lt; 370 K, and consequently Bi1-xSbx displays merely a tendency toward local segregation of Bi and Sb atoms, resulting in coexistence of Bi-rich and Sb-rich Bi1-xSbx solid solutions without the formation of any ordered structure of Bi1-xSbx as predicted in the absence of spin-orbit coupling. These findings distinctly highlight an influence of spin-orbit coupling on the alloying behavior of Bi1-xSbx and probably other alloys composed of heavy elements, where the spin-orbit-coupling effect is supposed to be robust.

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  • 39.
    Casillas Trujillo, Luis
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Gambino, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ventelon, Lisa
    Univ Paris Saclay, France.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Screw dislocation core structure in the paramagnetic state of bcc iron from first-principles calculations2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 9, artikel-id 094420Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Iron-based alloys are widely used as structural components in engineering applications. This calls for a fundamental understanding of their mechanical properties, including those of pure iron. Under operational temperatures the mechanical and magnetic properties will differ from those of ferromagnetic body-centered-cubic iron at 0 K. In this theoretical work we study the effect of disordered magnetism on the screw dislocation core structure and compare with results for the ordered ferromagnetic case. Dislocation cores control some local properties such as the choice of glide plane and the associated dislocation mobility. Changes in the magnetic state can lead to modifications in the structure of the core and affect dislocation mobility. In particular, we focus on the core properties of the 1/2 &lt; 111 &gt; screw dislocation in the paramagnetic state. Using the noncollinear disordered local moment approximation to address paramagnetism, we perform structural relaxations within density functional theory. We obtain the dislocation core structure for the easy and hard cores in the paramagnetic state, and compare them with their ferromagnetic counterparts. By averaging the energy of several disordered magnetic configurations, we obtain an energy difference between the easy- and hard-core configurations, with a lower, but statistically close, value than the one reported for the ferromagnetic case. The magnetic moment and atomic volume at the dislocation core differ between paramagnetic and ferromagnetic states, with possible consequences on the temperature dependence of defect-dislocation interactions.

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  • 40.
    Bakhit, Babak
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Palisaitis, Justinas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Persson, Per O.Å.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Rosen, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Materials Research Laboratory and Department of Materials Science, University of Illinois, Urbana IL 61801, USA; Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Materials Research Laboratory and Department of Materials Science, University of Illinois, Urbana IL 61801, USA; Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.
    Greczynski, Grzegorz
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Self-organized columnar Zr0.7Ta0.3B1.5 core/shell-nanostructure thin films2020Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 401, artikel-id 126237Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We recently showed that Zr1−xTaxBy thin films have columnar nanostructure in which column boundaries are B-rich for x < 0.2, while Ta-rich for x ≥ 0.2. Layers with x ≥ 0.2 exhibit higher hardness and, simultaneously, enhanced toughness. Here, we determine the atomic-scale nanostructure of sputter-deposited columnar Zr0.7Ta0.3B1.5 thin films. The columns, 95 ± 17 Å, are core/shell nanostructures in which 80 ± 15-Å cores are crystalline hexagonal-AlB2-structure Zr-rich stoichiometric Zr1−xTaxB2. The shell structure is a narrow dense, disordered region that is Ta-rich and highly B-deficient. The cores are formed under intense ion mixing via preferential Ta segregation, due to the lower formation enthalpy of TaB2 than ZrB2, in response to the chemical driving force to form a stoichiometric compound. The films with unique combination of nanosized crystalline cores and dense metallic-glass-like shells provide excellent mechanical properties.

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  • 41.
    Johansson, Erik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Minist Higher Educ Sci Res & Innovat, Thailand.
    Rosén, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Theoretical investigation of mixing and clustering thermodynamics of Ti1-xAlxB2 alloys with potential for age-hardening2020Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 128, nr 23, artikel-id 235101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metastable ternary ceramic alloys with clustering tendencies are candidates for hard coating applications. In this work, mixing thermodynamics and structural parameters of ceramic Ti1-xAlxB2 alloys are investigated with theoretical first-principles based techniques. Lattice dynamics and temperature dependent phase stability are explored. The effect of lattice vibrations on the total free energy is investigated and found to not significantly affect phase stability at temperatures below 1200K. The isostructural phase diagram is derived using both cluster expansion-based Monte Carlo simulations and a mean field approach. The phase diagram shows a miscibility gap that does not close at temperatures below the melting or decomposition temperatures of the constituent binaries TiB2 and AlB2. The lattice mismatch between phases in the system is small regardless of their composition even at elevated temperatures. These findings support the prospect of age hardening due to coherent isostructural decomposition, such as spinodal decomposition, in coatings of Ti(1-x)AlxB(2) as diffusion is activated at elevated temperature. (c) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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  • 42.
    Landälv, Ludvig
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Sandvik Coromant AB, Sweden.
    Gothelid, Emmanuelle
    Sandvik Coromant AB, Sweden.
    Jensen, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Greczynski, Grzegorz
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Ahlgren, Mats
    Sandvik Coromant AB, Sweden.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Influence of Si doping and O-2 flow on arc-deposited (Al,Cr)(2)O-3 coatings2019Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, nr 6, artikel-id 061516Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    (Al,Cr)(2)O-3 coatings with Al/( Al + Cr) = 0.5 or Al = 70 at. %, doped with 0, 5, or 10 at. % Si, were deposited on hard metal and Si(100) substrates to elucidate the influence of Si on the resulting coatings. The chemical analysis of the coatings showed between 3.3 and 7.4 at. % metal fraction Si incorporated into all studied coatings depending on cathode Si composition. The incorporated Si content does not change significantly with different oxygen flows covering a wide range of deposition conditions from low to high O-2 flow during growth. The addition of Si promotes the metastable B1-like cubic structure over the thermodynamically stable corundum structure. The hardness determined by nanoindentation of the as-deposited coatings is slightly reduced upon Si incorporation as well as upon increased Al content. Si is found enriched in droplets but can also be found at a lower content, evenly spread, without visible segregation at the similar to 5 nm scale, in the actual oxide coating. The positive effect of improved cathode erosion upon Si incorporation has to be balanced against the promotion of the metastable B1-like structure, having lower room temperature hardness and inferior thermal stability compared to the corundum structure. Published by the AVS.

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  • 43.
    Eklof, Daniel
    et al.
    Stockholm Univ, Sweden.
    Fischer, Andreas
    Augsburg Univ, Germany.
    Ektarawong, Annop
    Chulalongkorn Univ, Thailand; Commiss Higher Educ, Thailand.
    Jaworski, Aleksander
    Stockholm Univ, Sweden.
    Pell, Andrew J.
    Stockholm Univ, Sweden.
    Grins, Jekabs
    Stockholm Univ, Sweden.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Wu, Yang
    Tsinghua Univ, Peoples R China.
    Widom, Michael
    Carnegie Mellon Univ, PA 15213 USA.
    Scherer, Wolfgang
    Augsburg Univ, Germany.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Mysterious SiB3: Identifying the Relation between alpha- and beta-SiB32019Ingår i: ACS Omega, E-ISSN 2470-1343, Vol. 4, nr 20, s. 18741-18759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Binary silicon boride SiB3 has been reported to occur in two forms, as disordered and nonstoichiometric alpha-SiB3-x, which relates to the alpha-rhombohedral phase of boron, and as strictly ordered and stoichiometric beta-SiB3. Similar to other boron-rich icosahedral solids, these SiB3 phases represent potentially interesting refractory materials. However, their thermal stability, formation conditions, and thermodynamic relation are poorly understood. Here, we map the formation conditions of alpha-SiB3-x and beta-SiB3 and analyze their relative thermodynamic stabilities. alpha-SiB3-x is metastable (with respect to beta-SiB3 and Si), and its formation is kinetically driven. Pure polycrystalline bulk samples may be obtained within hours when heating stoichiometric mixtures of elemental silicon and boron at temperatures 1200-1300 degrees C. At the same time, alpha-SiB3-x decomposes into SiB6 and Si, and optimum time-temperature synthesis conditions represent a trade-off between rates of formation and decomposition. The formation of stable beta-SiB3 was observed after prolonged treatment (days to weeks) of elemental mixtures with ratios Si/B = 1:11:4 at temperatures 1175-1200 degrees C. The application of high pressures greatly improves the kinetics of SiB3 formation and allows decoupling of SiB3 formation from decomposition. Quantitative formation of beta-SiB3 was seen at 1100 degrees C for samples pressurized to 5.5-8 GPa. beta-SiB3 decomposes peritectoidally at temperatures between 1250 and 1300 degrees C. The highly ordered nature of beta-SiB3 is reflected in its Raman spectrum, which features narrow and distinct lines. In contrast, the Raman spectrum of alpha-SiB3-x is characterized by broad bands, which show a clear relation to the vibrational modes of isostructural, ordered B6P. The detailed composition and structural properties of disordered alpha-SiB3-x were ascertained by a combination of single-crystal X-ray diffraction and Si-29 magic angle spinning NMR experiments. Notably, the compositions of polycrystalline bulk samples (obtained at T amp;lt;= 1200 degrees C) and single crystal samples (obtained from Si-rich molten Si-B mixtures at T amp;gt; 1400 degrees C) are different, SiB2.93(7) and SiB2.64(2), respectively. The incorporation of Si in the polar position of B-12 icosahedra results in highly strained cluster units. This disorder feature was accounted for in the refined crystal structure model by splitting the polar position into three sites. The electron-precise composition of alpha-SiB3-x is SiB2.5 and corresponds to the incorporation of, on average, two Si atoms in each B-12 icosahedron. Accordingly, alpha-SiB3-x constitutes a mixture of B10Si2 and B11Si clusters. The structural and phase stability of alpha-SiB3-x were explored using a first-principles cluster expansion. The most stable composition at 0 K is SiB2.5, which however is unstable with respect to the decomposition beta-SiB3 + Si. Modeling of the configurational and vibrational entropies suggests that alpha-SiB3-x only becomes more stable than beta-SiB3 at temperatures above its decomposition into SiB6 and Si. Hence, we conclude that alpha-SiB3-x is metastable at all temperatures. Density functional theory electronic structure calculations yield band gaps of similar size for electron-precise alpha-SiB2.5 and beta-SiB3, whereas alpha-SiB3 represents a p-type conductor.

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  • 44.
    Landälv, Ludvig
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Sandvik Coromant AB, Stockholm, Sweden.
    Carlström, C-F
    Sandvik Coromant AB, Stockholm, Sweden.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Primetzhofer, D.
    Applied Nuclear Physics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Jöesaar, M. J.
    SECO Tools AB, Fagersta, Sweden.
    Ahlgren, M.
    Sandvik Coromant AB, Stockholm, Sweden.
    Göthelid, E.
    Sandvik Coromant AB, Stockholm, Sweden.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings2019Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, artikel-id 137369Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.

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  • 45.
    Landälv, Ludvig
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Sandvik Coromant AB, Sweden.
    Rogström, Lina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanostrukturerade material. Linköpings universitet, Tekniska fakulteten.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Ostach, Daniel
    Helmholtz Zentrum Geesthacht, Germany.
    Eriksson, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Junaid, Muhammad
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Ghafoor, Naureen
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Ekström, Erik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hsiao, Ching-Lien
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Leiste, Harald
    Karlsruhe Inst Technol, Germany.
    Ahlgren, Mats
    Sandvik Coromant AB, Sweden.
    Gothelid, Emmanuelle
    Sandvik Coromant AB, Sweden.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Stuber, Michael
    Karlsruhe Inst Technol, Germany.
    Schell, Norbert
    Helmholtz Zentrum Geesthacht, Germany.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Phase evolution of radio frequency magnetron sputtered Cr-rich (Cr,Zr)(2)O-3 coatings studied by in situ synchrotron X-ray diffraction during annealing in air or vacuum2019Ingår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 34, nr 22, s. 3735-3746Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phase evolution of reactive radio frequency (RF) magnetron sputtered Cr0.28Zr0.10O0.61 coatings has been studied by in situ synchrotron X-ray diffraction during annealing under air atmosphere and vacuum. The annealing in vacuum shows t-ZrO2 formation starting at similar to 750-800 degrees C, followed by decomposition of the alpha-Cr2O3 structure in conjunction with bcc-Cr formation, starting at similar to 950 degrees C. The resulting coating after annealing to 1140 degrees C is a mixture of t-ZrO2, m-ZrO2, and bcc-Cr. The air-annealed sample shows t-ZrO2 formation starting at similar to 750 degrees C. The resulting coating after annealing to 975 degrees C is a mixture of t-ZrO2 and alpha-Cr2O3 (with dissolved Zr). The microstructure coarsened slightly during annealing, but the mechanical properties are maintained, with no detectable bcc-Cr formation. A larger t-ZrO2 fraction compared with alpha-Cr2O3 is observed in the vacuum-annealed coating compared with the air-annealed coating at 975 degrees C. The results indicate that the studied pseudo-binary oxide is more stable in air atmosphere than in vacuum.

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  • 46.
    Pakornchote, T.
    et al.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Ektarawong, Annop
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Max Planck Inst Eisenforsch GmbH, Germany.
    Pinsook, U.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Tancharakorn, S.
    Synchrotron Light Res Inst Publ Org, Thailand.
    Busayaporn, W.
    Synchrotron Light Res Inst Publ Org, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Phase stabilities and vibrational analysis of hydrogenated diamondized bilayer graphenes: A first principles investigation2019Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 146, s. 468-475Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phase stabilities as well as some intrinsic properties of hydrogenated diamondized bilayer graphenes, 2-dimensional materials adopting the crystal structure of diamond and of lonsdaleite, are investigated using a first-principles approach. Our simulations demonstrate that hydrogenated diamondized bilayer graphenes are thermodynamically stable with respect to bilayer graphene and hydrogen molecule even at 0 GPa, and additionally they are found to withstand the physical change in structure up to at least 1000 K, ensuring their dynamical and thermal stabilities. The studied hydrogenated diamondized bilayer graphenes are predicted not only to behave as direct and wide band gap semiconductors, but also to have a remarkably high resistance to in-plane plastic deformation induced by indentation as implied by their high in-plane elastic constants comparable to those of diamond and of lonsdaleite. The mechanical stability of the materials is confirmed though the fulfilment of the Born stability criteria. Detailed analysis of phonon vibrational frequencies of hydrogenated diamondized bilayer graphenes reveals possible Raman active and IR active modes, which are found to be distinctly different from those of hydrogenated diamond-like amorphous carbon and defective graphene and thus could be used as a fingerprint for future experimental characterization of the materials. (c) 2019 Elsevier Ltd. All rights reserved.

  • 47.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Singapore, Singapore.
    Peng, Y. P.
    Natl Univ Singapore, Singapore.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Phase stability of three-dimensional bulk and two-dimensional monolayer As1-xSbx solid solutions from first principles2019Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, nr 24, artikel-id 245702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mixing thermodynamics of both three-dimensional bulk and two-dimensional monolayered alloys of As1-xSbx as a function of alloy composition and temperature are explored using a first-principles cluster-expansion method, combined with canonical Monte-Carlo simulations. We observe that, for the bulk phase, As1-xSbx alloy can exhibit not only chemical ordering of As and Sb atoms at x = 0.5 to form an ordered compound of AsSb stable upon annealing up to T approximate to 475 K, but also a miscibility gap at 475 K less than or similar to T less than or similar to 550 K in which two disordered solid solutions of As1-xSbx of different alloy compositions thermodynamically coexist. At T amp;gt; 550 K, a single-phase solid solution of bulk As1-xSbx is predicted to be stable across the entire composition range. These results clearly explain the existing uncertainties in the alloying behavior of bulk As1-xSbx alloy, as previously reported in the literature, and also found to be in qualitative and quantitative agreement with the experimental observations. Interestingly, the alloying behavior of As1-xSbx is considerably altered, as the dimensionality of the material reduces from the three-dimensional bulk state to the two-dimensional monolayered state-for example, a single-phase solid solution of monolayer As1-xSbx is predicted to be stable over the whole composition range at T amp;gt; 250 K. This distinctly highlights an influence of the reduced dimensionality on the alloying behavior of As1-xSbx.

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  • 48.
    Ektarawong, Annop
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Chulalongkorn Univ, Thailand; Natl Univ Singapore, Singapore; Natl Univ Singapore, Singapore; Thailand Ctr Excellence Phys, Thailand.
    Feng, Y. P.
    Natl Univ Singapore, Singapore.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Phase stability of two-dimensional monolayer As1-xPx solid solutions revealed by a first-principles cluster expansion2019Ingår i: Physical Review Materials, E-ISSN 2475-9953, Vol. 3, nr 5, artikel-id 054005Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The phase stability of two-dimensional monolayer As1-xPx solid solutions, exhibiting the puckered (alpha phase) and buckled (beta phase) structures are investigated using a first-principles cluster-expansion method. Canonical Monte Carlo simulations, together with harmonic approximation, are performed to capture the influences of thermally induced configurational disorder and lattice vibrations on the phase stability of monolayer As1-xPx. We first demonstrate that, as the temperature approaches 0 K, the monolayer As1-xPx displays a tendency toward phase separation into its constituent elemental phases, and thus no stable ordered structures of As1-xPx, both alpha and beta phases, are predicted to be thermodynamically stable. We further reveal with the inclusion of the lattice vibrational contributions that beta-As1-xPx is thermodynamically favored over alpha-As1-xPx, across the entire composition range even at 0 K and increasingly so at higher temperature, and a continuous series of disordered solid solution of beta-As1-xPx, where 0 amp;lt;= x amp;lt;= 1, is predicted at the temperature above 550 K. These findings not only indicate that the ordered structures of monolayer alpha-As1-xPx, and beta-As1-xPx, frequently studied in the literature, may not exist in nature, but also presumably suggest that monolayer alpha-As1-xPx is metastable with respect to monolayer beta-As1-xPx.

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  • 49.
    Mockuté, Aurelija
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Palisaitis, Justinas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Nedfors, Nils
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Berastegui, P.
    Uppsala Univ, Sweden.
    Broitman, Esteban
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska fakulteten. SKF Res and Technol Dev Ctr, Netherlands.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Näslund, Lars-Åke
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Patscheider, J.
    Evatec AG, Switzerland.
    Jansson, U.
    Uppsala Univ, Sweden.
    Persson, Per O A
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Rosén, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering2019Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 669, s. 181-187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    (Ti1-xAlx)B2+Delta films with a lateral composition gradient of x = [0.30-0.66] and Delta = [0.07-1.22] were deposited on an Al2O3 wafer by dual magnetron sputtering at 400 degrees C from sintered TiB2 and AlB2 targets. Composition analysis indicates that higher Ti:Al ratios favor overstoichiometry in B and a reduced incorporation of O. Transmission electron microscopy reveals distinctly different microstructures of Ti- and Al-rich compositions, with formation of characteristic conical growth features for the latter along with a lower degree of crystallinity and significantly less tissue phase from B segregation at the grain boundaries. For Al-rich films, phase separation into Ti- and Al-rich diboride nanometer-size domains is observed and interpreted as surface-initiated spinodal decomposition. The hardness of the films ranges from 14 to 28 GPa, where the higher values were obtained for the Ti-rich regions of the metal boride.

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  • 50.
    Pedersen, Henrik
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Kemi. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Högberg, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Ektarawong, Annop
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Chulalongkorn Univ, Thailand; Commiss Higher Educ, Thailand.
    Thermodynamic stability of hexagonal and rhombohedral boron nitride under chemical vapor deposition conditions from van der Waals corrected first principles calculations2019Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, nr 4, artikel-id 040603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin films of boron nitride (BN), particularly the sp(2)-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN), are interesting for several electronic applications, given the bandgaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800K and 1000-10000Pa, respectively. In this letter, the authors use the van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. The authors find that r-BN is the stable sp(2)-hybridized phase at CVD conditions, while h-BN is metastable. Thus, their calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

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