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  • 1.
    Li, Huanyu
    et al.
    Linköpings universitet, Institutionen för datavetenskap, Databas och informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Lambrix, Patrick
    Linköpings universitet, Institutionen för datavetenskap, Databas och informationsteknik. Linköpings universitet, Tekniska högskolan.
    A Method for Extending Ontologies with Application to the Materials Science Domain2019Ingår i: Data Science Journal, ISSN 1683-1470, E-ISSN 1683-1470, Vol. 18, nr 1, s. 1-21, artikel-id 50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the materials science domain the data-driven science paradigm has become the focus since the beginning of the 2000s. A large number of research groups and communities are building and developing data-driven workflows. However, much of the data and knowledge is stored in different heterogeneous data sources maintained by different groups. This leads to a reduced availability of the data and poor interoperability between systems in this domain. Ontology-based techniques are an important way to reduce these problems and a number of efforts have started. In this paper we investigate efforts in the materials science, and in particular in the nanotechnology domain, and show how such ontologies developed by domain experts, can be improved. We use a phrase-based topic model approach and formal topical concept analysis on unstructured text in this domain to suggest additional concepts and axioms for the ontology that should be validated by a domain expert. We describe the techniques and show the usefulness of the approach through an experiment where we extend two nanotechnology ontologies using approximately 600 titles and abstracts.

  • 2.
    Kindlund, H.
    et al.
    Univ Calif Los Angeles, CA 90095 USA.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Petrov, Ivan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA; Natl Taiwan Univ Sci and Technol, Taiwan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    A review of the intrinsic ductility and toughness of hard transition-metal nitride alloy thin films2019Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, artikel-id 137479Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Over the past decades, enormous effort has been dedicated to enhancing the hardness of refractory ceramic materials. Typically, however, an increase in hardness is accompanied by an increase in brittleness, which can result in intergranular decohesion when materials are exposed to high stresses. In order to avoid brittle failure, in addition to providing high strength, films should also be ductile, i.e., tough. However, fundamental progress in obtaining hard-yet-ductile ceramics has been slow since most toughening approaches are based on empirical trial-and-error methods focusing on increasing the strength and ductility extrinsically, with a limited focus on understanding thin-film toughness as an inherent physical property of the material. Thus, electronic structure investigations focusing on the origins of ductility vs. brittleness are essential in understanding the physics behind obtaining both high strength and high plastic strain in ceramics films. Here, we review recent progress in experimental validation of density functional theory predictions on toughness enhancement in hard ceramic films, by increasing the valence electron concentration, using examples from the V1-xWxN and V1-xMoxN alloy systems.

  • 3.
    Vorotilo, S.
    et al.
    Natl Univ Sci and Technol MISIS, Russia.
    Sidnov, K.
    Natl Univ Sci and Technol MISIS, Russia; Russian Acad Sci, Russia.
    Mosyagin, I. Yu
    Natl Univ Sci and Technol MISIS, Russia.
    Khvan, A. V
    Natl Univ Sci and Technol MISIS, Russia.
    Levashov, E. A.
    Natl Univ Sci and Technol MISIS, Russia.
    Patsera, E. I
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Ab-initio modeling and experimental investigation of properties of ultra-high temperature solid solutions TaxZr1-xC2019Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 778, s. 480-486Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to their high melting temperature, high-temperature oxidation resistance and outstanding mechanical properties, TaxZr1-xC solid solutions are promising ultra-high temperature ceramics (UHTC). However, accelerated knowledge-based development of UHTCs solid solutions requires reliable data regarding the properties of the solution phases in the whole interval of concentrations. At present, there are contradictory reports regarding the existence of the miscibility gap in Ta-Zr-C system at temperatures below 900 degrees C. In this work, we carry out ab-initio calculations of the thermodynamic properties of TaxZr1-xC alloys and demonstrate that the solid solutions should not decompose into TaC and ZrC end member compounds. We synthesize single-phase samples of TaxZr1-xC with compositions x = 0.9, 0.8, 0.6, and 0.3 by self-propagating high-temperature synthesis (SHS) and anneal the samples for 40 h. We do not observe any sign of the decomposition of the solid solution during the annealing, corroborating the conclusions obtained by theoretical simulations. (C) 2018 Elsevier B.V. All rights reserved.

    Publikationen är tillgänglig i fulltext från 2020-11-19 15:39
  • 4.
    Mei, Antonio B.
    et al.
    Cornell Univ, NY 14853 USA; Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA.
    Miao, Ludi
    Cornell Univ, NY 14853 USA.
    Wahila, Matthew J.
    Binghamton Univ, NY 13902 USA.
    Khalsa, Guru
    Cornell Univ, NY 14853 USA.
    Wang, Zhe
    Cornell Univ, NY 14853 USA.
    Barone, Matthew
    Cornell Univ, NY 14853 USA.
    Schreiber, Nathaniel J.
    Cornell Univ, NY 14853 USA.
    Noskin, Lindsey E.
    Cornell Univ, NY 14853 USA.
    Paik, Hanjong
    Cornell Univ, NY 14853 USA.
    Tiwald, Thomas E.
    JA Woollam Co, NE 68508 USA.
    Zheng, Qiye
    Univ Illinois, IL 61801 USA; Lawrence Berkeley Natl Lab, CA 94720 USA; Univ Calif Berkeley, CA 94720 USA.
    Haasch, Richard T.
    Univ Illinois, IL 61801 USA.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Piper, Louis F. J.
    Binghamton Univ, NY 13902 USA.
    Schlom, Darrell G.
    Cornell Univ, NY 14853 USA; Kavli Inst Cornell Nanoscale Sci, NY 14853 USA.
    Adsorption-controlled growth and properties of epitaxial SnO films2019Ingår i: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, nr 10, artikel-id 105202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When it comes to providing the unusual combination of optical transparency, p-type conductivity, and relatively high mobility, Sn2+-based oxides are promising candidates. Epitaxial films of the simplest Sn2+ oxide, SnO, are grown in an adsorption-controlled regime at 380 degrees C on Al2O3 substrates by molecular-beam epitaxy, where the excess volatile SnOx desorbs from the film surface. A commensurately strained monolayer and an accompanying van der Waals gap is observed near the substrate interface, promoting layers with high structural perfection notwithstanding a large epitaxial lattice mismatch (-12%). The unintentionally doped films exhibit p-type conductivity with carrier concentration 2.5 x 10(16) cm(-3) and mobility 2.4 cm(2) V(-1)s(-1) at room temperature. Additional physical properties are measured and linked to the Sn2+ valence state and corresponding lone-pair charge-density distribution.

  • 5.
    Marcus, Carina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Saab AB, Broderna Ugglas Vag, SE-58188 Linkoping, Sweden; Swedish Def Univ, Sweden.
    Aspects of the design, evaluation and accuracy of airborne sensor clusters using time-difference of arrival2019Ingår i: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 92, s. 892-900Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One way of improving situational awareness without increasing the risk of detection is to use passive sensor systems. If this capability is provided by several aircraft in a cluster, which can incorporate small basic sensor platforms, advantages can be gained such as longer baselines and an increased number of sensors in the cluster. In this paper, a methodology is presented that links results from signal processing to a Design Space Exploration, DSE, regarding sensor clusters when designing clusters that can operate both independently and in cooperation with other systems. When using Time-Difference of Arrival, the accuracy of the estimated location of a signal source depends on errors in timing and positioning of the sensors, errors in estimating signal arrival times and number of sensors and their spatial distribution. The Cramer-Rao Lower Bound is used to investigate the accuracy of signal source estimates for five different clusters and two levels of timing and positioning accuracy. The results show that the direction of arrival estimates are more accurate than those for the range. Although more sensors generally increased the accuracy, their spatial distribution and baseline related to the distance to the signal source also influence the quality of the results. The DSE process is supported by the collected presentation of the data regarding the measurement accuracy of the different sensor configurations, incorporating both cluster configuration as well as the positioning and timing. Having readily accessible data, the decision makers can focus on choosing the sensor system that meets the operational needs. (C) 2019 Elsevier Masson SAS. All rights reserved.

  • 6.
    Jamnig, Andreas
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten. Univ Poitiers, France.
    Sangiovanni, Davide Giuseppe
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Abadias, G.
    Univ Poitiers, France.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Atomic-scale diffusion rates during growth of thin metal films on weakly-interacting substrates2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 6640Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use a combined experimental and theoretical approach to study the rates of surface diffusion processes that govern early stages of thin Ag and Cu film morphological evolution on weakly-interacting amorphous carbon substrates. Films are deposited by magnetron sputtering, at temperatures T-S between 298 and 413 K, and vapor arrival rates F in the range 0.08 to 5.38 monolayers/s. By employing in situ and real-time sheet-resistance and wafer-curvature measurements, we determine the nominal film thickness Theta at percolation (Theta(perc)) and continuous film formation (Theta(cont)) transition. Subsequently, we use the scaling behavior of Theta(perc) and Theta(cont) as a function of F and T-s, to estimate, experimentally, the temperature-dependent diffusivity on the substrate surface, from which we calculate Ag and Cu surface migration energy barriers E-D(exp) and attempt frequencies nu(exp)(0). By critically comparing E-D(exp) and nu(exp)(0) with literature data, as well as with results from our ab initio molecular dynamics simulations for single Ag and Cu adatom diffusion on graphite surfaces, we suggest that: (i) E-D(exp) and nu(exp)(0) correspond to diffusion of multiatomic clusters, rather than to diffusion of monomers; and (ii) the mean size of mobile clusters during Ag growth is larger compared to that of Cu. The overall results of this work pave the way for studying growth dynamics in a wide range of technologically-relevant weakly-interacting film/substrate systems-including metals on 2D materials and oxides-which are building blocks in next-generation nanoelectronic, optoelectronic, and catalytic devices.

  • 7.
    Yakymenko, Ivan
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Yakymenko, Irina I.
    Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Berggren, Karl-Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Basic modelling of effects of geometry and magnetic field for quantum wires injecting electrons into a two-dimensional electron reservoir2019Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, nr 34, artikel-id 345302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-mobility two-dimensional electron gas (2DEG) which resides at the interface between GaAs and AlGaAs layered semiconductors has been used experimentally and theoretically to study ballistic electron transport. The present paper is motivated by recent experiments in magnetic electron focusing. The proposed device consists of two quantum point contacts (QPCs) serving as electron injector and collector which are placed in the same semiconductor GaAs/AlGaAs heterostructure. Here we focus on a theoretical study of the injection of electrons via a quantum wire/QPC into an open two-dimensional (2D) reservoir. The transport is considered for non-interacting electrons at different transmission regimes using the mode-matching technique. The proposed mode-matching technique has been implemented numerically. Electron flow through the quantum wire with hard-wall rectangular, conical and rounded openings has been studied. We have found for these three cases that the geometry of the opening does not play a crucial role for the electron propagation. When a perpendicular magnetic field is applied the electron paths in the 2D reservoir are curved. We analyse this case both classically and quantum-mechanically. The effect of spin-splitting due to exchange interactions on the electron flow is also considered. The effect is clearly present for realistic choices of device parameters and consistent with observations. The results of this study may be applied in designing magnetic focusing devices and spin separation.

    Publikationen är tillgänglig i fulltext från 2020-06-04 08:00
  • 8.
    Silva, Gesiel Gomes
    et al.
    Goias Fed Inst Educ Sci and Technol, Brazil.
    Ribeiro, Luiz Antonio
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Brasilia, Brazil; Univ Brasilia, Brazil.
    Pereira Junior, Marcelo Lopes
    Univ Brasilia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    Univ Brasilia, Brazil; Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Bipolaron Dynamics in Graphene Nanoribbons2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 2909Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Graphene nanoribbons (GNRs) are two-dimensional structures with a rich variety of electronic properties that derive from their semiconducting band gaps. In these materials, charge transport can occur via a hopping process mediated by carriers formed by self-interacting states between the excess charge and local lattice deformations. Here, we use a two-dimensional tight-binding approach to reveal the formation of bipolarons in GNRs. Our results show that the formed bipolarons are dynamically stable even for high electric field strengths when it comes to GNRs. Remarkably, the bipolaron dynamics can occur in acoustic and optical regimes concerning its saturation velocity. The phase transition between these two regimes takes place for a critical field strength in which the bipolaron moves roughly with the speed of sound in the material.

  • 9.
    Leonov, Ivan
    et al.
    Russian Acad Sci, Russia; Natl Univ Sci and Technol MISIS, Russia.
    Rozenberg, Gregory Kh
    Tel Aviv Univ, Israel.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Charge disproportionation and site-selective local magnetic moments in the post-perovskite-type Fe2O3 under ultra-high pressures2019Ingår i: NPJ COMPUTATIONAL MATERIALS, ISSN 2057-3960, Vol. 5, artikel-id 90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The archetypal 3d Mott insulator hematite, Fe2O3, is one of the basic oxide components playing an important role in mineralogy of Earths lower mantle. Its high pressure-temperature behavior, such as the electronic properties, equation of state, and phase stability is of fundamental importance for understanding the properties and evolution of the Earths interior. Here, we study the electronic structure, magnetic state, and lattice stability of Fe2O3 at ultra-high pressures using the density functional plus dynamical mean-field theory (DFT + DMFT) approach. In the vicinity of a Mott transition, Fe2O3 is found to exhibit a series of complex electronic, magnetic, and structural transformations. In particular, it makes a phase transition to a metal with a post-perovskite crystal structure and site-selective local moments upon compression above 75 GPa. We show that the site-selective phase transition is accompanied by a charge disproportionation of Fe ions, with Fe-3 +/-delta and delta similar to 0.05-0.09, implying a complex interplay between electronic correlations and the lattice. Our results suggest that site-selective local moments in Fe2O3 persist up to ultra-high pressures of similar to 200-250 GPa, i.e., sufficiently above the core-mantle boundary. The latter can have important consequences for understanding of the velocity and density anomalies in the Earths lower mantle.

  • 10.
    Tal, Alexey A.
    et al.
    Ecole Polytech Fed Lausanne, Switzerland.
    Posada-Borbon, Alvaro
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Gronbeck, Henrik J.
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Correlation between Ethylene Adsorption Energies and Core-Level Shifts for Pd Nanoclusters2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 4, s. 2544-2548Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional theory calculations have been used to investigate the adsorption of ethylene on Pd nanoclusters together with shifts in core-level binding energies of Pd atoms bonded to the adsorbate. The adsorption energy is found to correlate with the core-level shifts (CLS), which is consistent with the notion that the core-level binding energy is a measure of differences in cohesion. The correlation between adsorption energies and core-level shifts is found to be stronger than the correlation between adsorption energies and generalized coordination numbers, indicating that descriptors preferably should account for electronic effects explicitly. The advantages of CLS as a descriptor for the screening of adsorption properties is discussed.

    Publikationen är tillgänglig i fulltext från 2019-12-24 10:57
  • 11.
    Marcus, Carina
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Saab AB, Aeronaut, Broderna Ugglas Gata, SE-58188 Linkoping, Sweden; Swedish Def Univ, Sweden.
    Raf, Martin
    Saab AB, Aeronaut, Broderna Ugglas Gata, SE-58188 Linkoping, Sweden.
    Detection Chain Model Designed for Aircraft Concept Development2019Ingår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 56, nr 5, s. 1942-1950Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Simultaneous design of an aircraft and its sensor systems offers advantages over integrating standard sensors because the need for sensor function can be balanced against the integration issues. A model of the detection chain is here defined as mathematical representations of the sensors, the wave propagation, and the signatures of the target. When used in aircraft concept development in a design space exploration context, the model of the detection chain needs to be simple yet detailed enough to sufficiently describe both the sensor performance and the impact it has on the infrastructure of the aircraft. In this paper a detection chain model for radar is introduced. It includes the detection range, search volume, and signature together with implications in terms of the aircraft infrastructure the parameters of mass, the volume, and power and cooling requirements as a function of antenna size. The best choice of radar cannot be determined by the sensor function alone; it has to be evaluated together with the aircraft in tactical simulations in order to obtain the complete picture. The benefits of a larger antenna can, to some degree, be counteracted by the changes to the aircraft that affect its flight performance.

  • 12.
    de Sousa, Leonardo Evaristo
    et al.
    Univ Brasilia, Brazil.
    Bueno, Fernando Teixeira
    Univ Brasilia, Brazil.
    da Silva Filho, Demetrio Antonio
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Dynamical exciton decay in organic materials: the role of bimolecular recombination2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 4, s. 1711-1716Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Excitons play a critical role in light emission when it comes to organic semiconductors. In high exciton concentration regimes, monomolecular and bimolecular routes for exciton recombination can yield different products affecting significantly the materials optical properties. Here, the dynamical decay of excitons is theoretically investigated using a kinetic Monte Carlo approach that addresses singlet exciton diffusion. Our numerical protocol includes two distinct exciton-exciton interaction channels: exciton annihilation and biexciton cascade emission. Our findings reveal that these channels produce different consequences concerning diffusion and spectroscopic properties, being able to explain diverging experimental observations. Importantly, we estimate critical exciton densities for which bimolecular recombination becomes dominant and investigate its effect on average exciton lifetimes and diffusion lengths.

  • 13.
    Heine, Matthew
    et al.
    Boston Coll, MA 02467 USA.
    Hellman, Olle
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Broido, David
    Boston Coll, MA 02467 USA.
    Effect of thermal lattice and magnetic disorder on phonons in bcc Fe: A first-principles study2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 10, artikel-id 104304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a first-principles theoretical approach to calculate temperature dependent phonon dispersions in bcc Fe, which captures finite temperature spin-lattice coupling by treating thermal disorder in both the spin and lattice systems simultaneously. With increasing temperature, thermal atomic displacements are found to induce increasingly large fluctuations in local magnetic moment magnitudes. The calculated phonon dispersions of bcc Fe show excellent agreement with measured data over a wide range of temperatures both above and below the magnetic and structural transition temperatures, suggesting the applicability of the developed approach to other magnetic materials.

  • 14.
    Pilemalm, Robert
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    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.
    Effects of high pressure on ScMN2-type (M = V, Nb, Ta) phases studied by density functional theory2019Ingår i: Results in Physics, ISSN 2211-3797, Vol. 13, artikel-id 102293Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb, but their high-pressure properties have not been studied. Here, we have used first-principles calculations to study their thermodynamic stability, elastic and electronic properties at high-pressure. We have used density functional theory to calculate the formation enthalpy relative to the competing binary phases, electronic density of states and elastic constants (c(ij)), bulk (B), shear (G) and Youngs (E) modulus as the pressure is varied from 0 to 150 GPa. Our results show that when the pressure increases from 0 to 150 GPa, elastic constants, bulk, shear and elastic moduli increase in the range 53-216% for ScTaN2, 72-286% for ScNbN2, and 61-317% for ScVN2.

  • 15.
    Spektor, Kristina
    et al.
    ESRF, France.
    Crichton, Wilson A.
    ESRF, France.
    Filippov, Stanislav
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Stockholm Univ, Sweden.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Exploring the Mg-Cr-H System at High Pressure and Temperature via in Situ Synchrotron Diffraction2019Ingår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, nr 16, s. 11043-11050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The complex transition metal hydride Mg3CrH8 has been previously synthesized using high pressure conditions. It contains the first group 6 homoleptic hydrido complex, [Cr(II)H-7](5-). Here, we investigated the formation of Mg3CrH8 by in situ studies of reaction mixtures of 3MgH(2)-Cr-H-2 at 5 GPa. The formation of the known orthorhombic form (o-Mg3CrH8) was noticed at temperatures above 635 degrees C, albeit at a relatively slow rate. At temperatures around 750 degrees C a high temperature phase formed rapidly, which upon slow cooling converted into o-Mg3CrH8. The phase transition at high pressures occurred reversibly at similar to 735 degrees C upon heating and at similar to 675 degrees C upon slow cooling. Upon rapid cooling, a monoclinic polymorph (m-Mg3CrH8) was afforded which could be subsequently recovered and analyzed at ambient pressure. m-Mg3CrH8 was found to crystallize in P2(1)/n space group (a = 5.128 angstrom, b = 16.482 angstrom, c = 4.805 angstrom, beta = 90.27 degrees). Its structure elucidation from high resolution synchrotron powder diffraction data was aided by first-principles DFT calculations. Like the orthorhombic polymorph, m-Mg3CrH8 contains pentagonal bipyramidal complexes [CrH7](5-) and interstitial H-. The arrangement of metal atoms and interstitial H- resembles closely that of the high pressure orthorhombic form of Mg3MnH7. This suggests similar principles of formation and stabilization of hydrido complexes at high pressure and temperature conditions in the Mg-Cr-H and Mg-Mn-H systems. Calculated enthalpy versus pressure relations predict o-Mg3CrH8 being more stable than m-Mg3CrH8 by 6.5 kJ/mol at ambient pressure and by 13 kJ/mol at 5 GPa. The electronic structure of m-Mg3CrH8 is very similar to that of o-Mg3CrH8. The stable 18-electron complex [CrH7](5-) is mirrored in the occupied states, and calculated band gaps are around 1.5 eV.

  • 16.
    Ferrari, Alberto
    et al.
    Ruhr Univ Bochum, Germany.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Rogal, Jutta
    Ruhr Univ Bochum, Germany.
    Drautz, Ralf
    Ruhr Univ Bochum, Germany.
    First-principles characterization of reversible martensitic transformations2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 9, artikel-id 094107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reversible martensitic transformations (MTs) are the origin of many fascinating phenomena, including the famous shape memory effect. In this work, we present a fully ab initio procedure to characterize MTs in alloys and to assess their reversibility. Specifically, we employ ab initio molecular dynamics data to parametrize a Landau expansion for the free energy of the MT. This analytical expansion makes it possible to determine the stability of the high- and low-temperature phases, to obtain the Ehrenfest order of the MT, and to quantify its free energy barrier and latent heat. We apply our model to the high-temperature shape memory alloy Ti-Ta, for which we observe remarkably small values for the metastability region (the interval of temperatures in which the high-and low-temperature phases are metastable) and for the barrier: these small values are necessary conditions for the reversibility of MTs and distinguish shape memory alloys from other materials.

  • 17.
    Parra-Rivas, Pedro
    et al.
    Univ Libre Bruxelles, Belgium; Univ Leuven, Belgium.
    Gelens, Lendert
    Univ Leuven, Belgium.
    Hansson, Tobias
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Wabnitz, Stefan
    Sapienza Univ Rome, Italy; CNR, Italy.
    Leo, Francois
    Univ Libre Bruxelles, Belgium.
    Frequency comb generation through the locking of domain walls in doubly resonant dispersive optical parametric oscillators2019Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 44, nr 8, s. 2004-2007Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this Letter we theoretically investigate the formation of localized temporal dissipative structures, and their corresponding frequency combs in doubly resonant dispersive optical parametric oscillators. We derive a nonlocal mean field model, and show that domain wall locking allows for the formation of stable coherent optical frequency combs. (C) 2019 Optical Society of America

  • 18.
    Laniel, Dominique
    et al.
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Ponomareva, Alena V.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Glazyrin, Konstantin
    DESY, Germany.
    Svitlyk, Volodymyr
    European Synchrotron Radiat Facil, France.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    High Pressure Investigation of the S-N-2 System up to the Megabar Range: Synthesis and Characterization of the SN2 Solid2019Ingår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, nr 14, s. 9195-9204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions, however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur nitrogen compounds. Above 64 GPa, an orthorhombic (space group Pnnm) SN2 compound was synthesized and characterized by single-crystal and powder X-ray diffraction as well as Raman spectroscopy. It is shown to adopt a CaCl2-type structure hence it is isostructural, isomassic, and isoelectronic to CaCl2-type SiO2 comprised of SN6 octahedra. Complementary theoretical calculations were performed to provide further insight into the physicochemical properties of SN2, notably its equation of state, the bonding type between its constitutive elements, and its electronic density of states. This new solid is shown to be metastable down to about 20 GPa, after which it spontaneously decomposes into S and N-2. This investigation shows that despite the many metastable S N compounds existing at ambient conditions, none of them are formed by pressure.

  • 19.
    Bykov, Maxim
    et al.
    Univ Bayreuth, Germany.
    Chariton, Stella
    Univ Bayreuth, Germany.
    Fei, Hongzhan
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Ponomareva, Alena V
    Natl Univ Sci and Technol MISIS, Russia.
    Tasnadi, Ferenc
    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.
    Merle, Benoit
    Friedrich Alexander Univ Erlangen Nurnberg FAU, Germany.
    Feldners, Patrick
    Friedrich Alexander Univ Erlangen Nurnberg FAU, Germany.
    Vogel, Sebastian
    Univ Munich LMU, Germany.
    Schnick, Wolfgang
    Univ Munich LMU, Germany.
    Prakapenka, Vitali B.
    Univ Chicago, IL 60637 USA.
    Greenberg, Eran
    Univ Chicago, IL 60637 USA.
    Hanfland, Michael
    European Synchrotron Radiat Facil, France.
    Pakhomova, Anna
    DESY, Germany.
    Liermann, Hanns-Peter
    DESY, Germany.
    Katsura, Tomoo
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re-2(N-2)(N)(2) stable at ambient conditions2019Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, artikel-id 2994Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K-0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re-2(N-2)(N)(2). Unlike known transition metals pernitrides Re-2(N-2)(N)(2) contains both pernitride N-2(4-) and discrete N3- anions, which explains its exceptional properties. Re-2(N-2)(N)(2) can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re-2(N-2)(N)(2) turned to be at a threshold for superhard materials.

  • 20.
    Davidsson, Joel
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ivády, Viktor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Nguyen, Son Tien
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Identification of divacancy and silicon vacancy qubits in 6H-SiC2019Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, nr 11, artikel-id 112107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Point defects in semiconductors are relevant for use in quantum technologies as room temperature qubits and single photon emitters. Among suggested defects for these applications are the negatively charged silicon vacancy and the neutral divacancy in SiC. The possible nonequivalent configurations of these defects have been identified in 4H-SiC, but for 6H-SiC, the work is still in progress. In this paper, we identify the different configurations of the silicon vacancy and the divacancy defects to each of the V1-V3 and the QL1-QL6 color centers in 6H-SiC, respectively. We accomplish this by comparing the results from ab initio calculations with experimental measurements for the zero-phonon line, hyperfine tensor, and zero-field splitting. Published under license by AIP Publishing.

  • 21.
    Ekeroth, Sebastian
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Ikeda, Shuga
    Department of Intelligent Mechanical Systems, Tokyo Metropolitan University, Tokyo, Japan.
    Boyd, Robert
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Shimizu, Tetsuhide
    Department of Intelligent Mechanical Systems, Tokyo Metropolitan University, Tokyo, Japan.
    Helmersson, Ulf
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Impact of nanoparticle magnetization on the 3D formation of dual-phase Ni/NiO nanoparticle-based nanotrusses2019Ingår i: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 21, nr 11, artikel-id 21:228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic nanoparticles with average size 30 nm were utilized to build three-dimensional framework structures—nanotrusses. In dual-phase Ni/NiO nanoparticles, there is a strong correlation between the amount of magnetic Ni and the final size and shape of the nanotruss. As it decreases, the length of the individual nanowires within the trusses also decreases, caused by a higher degree of branching of the wires. The position and orientation of the non-magnetic material within the truss structure was also investigated for the different phase compositions. For lower concentrations of NiO phase, the electrically conducting Ni-wire framework is maintained through the preferential bonding between the Ni crystals. For larger concentrations of NiO phase, the Ni-wire framework is interrupted by the NiO. The ability to use nanoparticles that are only partly oxidized in the growth of nanotruss structures is of great importance. It opens the possibility for using not only magnetic metals such as pure Ni, Fe, and Co, but also to use dual-phase nanoparticles that can strongly increase the efficiency of e.g. catalytic electrodes and fuel cells.

  • 22.
    Jönsson, Johan
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Ekholm, Marcus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    van Smaalen, Sander
    Univ Bayreuth, Germany.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Inverse pressure-induced Mott transition in TiPO42019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 24, artikel-id 245132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.

  • 23.
    Stojanović, M.G.
    et al.
    Vinča Institute of Nuclear Sciences, Belgrade.
    Stojanović Krasić, M.
    University of Niš.
    Johansson, Magnus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Salinas, I.A.
    Universidad de Chile.
    Vicencio, R.A.
    Universidad de Chile.
    Stepić, M.
    Vinča Institute of Nuclear Sciences,.
    Localized modes in two-dimensional octagonal-diamond lattices2019Ingår i: Book of abstracts PHOTONICA2019: ABSTRACTS OF TUTORIAL, KEYNOTE, INVITED LECTURES, PROGRESS REPORTS AND CONTRIBUTED PAPERS / [ed] Milica Matijević, Marko Krstić and Petra Beličev, Belgrade, Serbia: Vinča Institute of Nuclear Sciences , 2019, s. 93-93Konferensbidrag (Refereegranskat)
    Abstract [en]

    Two-dimensional octagonal-diamond (OD) atomic lattices have been explored in recent times to study phenomena related to topological phase transitions induced by spin-orbit interaction and gauge fields [1], and magnetic phases and metal-insulator transitions with Hubbard interaction [2,3]. It can lead to the appearance of nontrivial nearly flat band states with particular topological properties [4]. Here we study the octagonal-diamond photonic lattice formed of linearly coupled waveguides, proposed by [4] as a possible experimental realization of an artificial flat-band system.

    We investigated analytically and numerically the existence and stability of linear and nonlinear localized modes in a two-dimensional OD lattice. The primitive cell consists of four sites, linearly coupled with each other with the same coupling constant, including two diagonal couplings. The eigenvalue spectrum of the linear lattice consists of two flat bands and two dispersive bands [4]. The upper dispersive band intersects the upper flat band in the middle of the Brillouin zone, as well as the second flat band at the end of the Brillouin zone. In the linear case, there are two types of localized linear solutions, which are composed of eight sites each, having either monomer (+ - + - + - + -) or dimer (+ + - - + + - -) staggered phase structure [4]. In the presence of Kerr nonlinearity, both focusing and defocusing, compacton-like solutions [5] may exhibit instabilities due to intersections of the upper dispersive band and the flat bands. We also discuss the possibility of finding soliton solutions in the frequency gaps occurring between the flat bands and the isolated dispersive bands.

    REFERENCES

    [1] M. Kargarian, G. A. Fiete, Phys. Rev. B 82, 085106 (2010).

    [2] Y. Yamashita et al., Phys. Rev. B 88, 195104 (2013).

    [3] A. Bao et al., Sci. Rep. 4, 6918 (2014).

    [4] B. Pal, Phys. Rev. B 98, 245116 (2018).

    [5] R. A. Vicencio, M. Johansson, Phys. Rev. A 87, 061803(R) (2013).

  • 24.
    Belonoshko, Anatoly B.
    et al.
    Royal Inst Technol KTH, Sweden.
    Fu, Jie
    Ningbo Univ, Peoples R China.
    Bryk, Taras
    Natl Acad Sci Ukraine, Ukraine.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Mattesini, Maurizio
    Univ Complutense Madrid, Spain; UCM, Spain.
    Low viscosity of the Earths inner core2019Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, artikel-id 2483Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Earths solid inner core is a highly attenuating medium. It consists mainly of iron. The high attenuation of sound wave propagation in the inner core is at odds with the widely accepted paradigm of hexagonal close-packed phase stability under inner core conditions, because sound waves propagate through the hexagonal iron without energy dissipation. Here we show by first-principles molecular dynamics that the body-centered cubic phase of iron, recently demonstrated to be thermodynamically stable under the inner core conditions, is considerably less elastic than the hexagonal phase. Being a crystalline phase, the body-centered cubic phase of iron possesses the viscosity close to that of a liquid iron. The high attenuation of sound in the inner core is due to the unique diffusion characteristic of the body-centered cubic phase. The low viscosity of iron in the inner core enables the convection and resolves a number of controversies.

  • 25.
    Klarbring, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Low-energy paths for octahedral tilting in inorganic halide perovskites2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 10, artikel-id 104105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Instabilities relating to cooperative octahedral tilting is common in materials with perovskite structures, in particular in the subclass of halide perovskites. In this work the energetics of octahedral tilting in the inorganic metal halide perovskites CsPbI3 and CsSnI3 are investigated using first-principles density functional theory calculations. Several low-energy paths between symmetry equivalent variants of the stable orthorhombic (Pnma) perovskite variant are identified and investigated. The results are in favor of the presence of dynamic disorder in the octahedral tilting phase transitions of inorganic halide perovskites. In particular, one specific type of path, corresponding to an out-of-phase "tilt switch," is found to have significantly lower energy barrier than the others, which indicates the existence of a temperature range where the dynamic fluctuations of the octahedra follow only this type of path. This could produce a time averaged structure corresponding to the intermediate tetragonal (P4/mbm) structure observed in experiments. Deficiencies of the commonly employed simple one-dimensional "double-well" potentials in describing the dynamics of the octahedra are pointed out and discussed.

  • 26.
    Sangiovanni, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Mass transport properties of quasiharmonic vs. anharmonic transition-metal nitrides2019Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, artikel-id 137297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    I present a development of the color-diffusion algorithm, used in non-equilibrium (accelerated) ab initio molecular dynamics simulations of point-defect migration in crystals [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)], to determine the temperature dependence of anion vacancy jump frequencies in rocksalt-structure (B1) TiN and VN characterized by quasiharmonic (TiN) vs. strongly anharmonic (VN) lattice dynamics. Over a temperature range [ 0.6"Tm amp;lt; T amp;lt; 0.9 T-m] relatively close to the materials melting points Tm, the simulations reveal that anion vacancy migration in TiN and VN exhibits an Arrhenius-like behavior, described by activation energies EJN = 4.2 0.3 eV and EZN = 3.1 0.3 eV, and attempt frequencies vTN = 8.1015 0.7 s-1 and vvN = 2.1017 c).8s-1. A comparison of activation energies E extracted by Arrhenius linear regression at elevated temperatures with ab initio E,,ca values calculated at 0 Kelvin reveals that, while the nitrogen migration energy amp;ills varies modestly with temperature {AEPN = [E-a(T-m)- Ea(0 K)1/Ea(0 K) 0.1}, the changes in EavN vs. T are considerable (AEavN 1). The temperature-induced variations in vacancy migration energies and diffusivities are discussed in relation to the TiN and VN vibrational properties determined via ab initio molecular dynamics at different temperatures. It is argued that static 0-K calculations, which account for thermal expansion effects within the framework of quasiharmonic transition-state theory, accurately reproduce the finite-temperature mass transport properties of TiN. Conversely, the use of molecular dynamics simulations, which explicit treat lattice vibrations at any temperature of interest, is necessary to achieve reliable atomic diffusivities in B1 VN, a crystal phase dynamically stabilized by anharmonic vibrations [Mei et al., Phys. Rev. B 91, 054101 (2015)].

  • 27.
    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, 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.

  • 28.
    Krasilnikov, O. M.
    et al.
    NUST MISIS, Russia.
    Lugovskoy, A. V
    NUST MISIS, Russia; Radboud Univ Nijmegen, Netherlands.
    Dikan, V
    NUST MISIS, Russia; CSIC, Spain.
    Belov, M. P.
    NUST MISIS, Russia.
    Vekilov, Yu Kh
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. NUST MISIS, Russia.
    Nonlinear elasticity of epsilon -Fe: The pressure effect2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 18, artikel-id 184101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Description of elasticity of iron at the ultrahigh pressures is a challenging task for physics, with a potential strong impact on other branches of science. In the present work, we calculate the elastic properties of hcp iron in the pressure range of 50-340 GPa beyond the linear elasticity approximation, conventionally assumed in theoretical studies. We define the higher order elastic constants and present expressions for the long-wave acoustic modes Gruneisen parameters of a compressed hcp crystal. We obtain the second and third order elastic constants of the hcp Fe in the considered pressure interval, as well as its Gruneisen parameters for the high-symmetry directions. The latter are directly compared with the Gruneisen parameters derived from the volume dependences of the vibrational frequencies calculated in the quasiharmonic approximation. The obtained results are used for the stability analysis of the hcp phase of iron at high pressures.

  • 29.
    Johansson, Magnus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik.
    Beličev, Petra P
    University of Belgrade.
    Gligorić, Goran
    University of Belgrade.
    Gulevich, Dmitry R.
    ITMO University.
    Skryabin, Dmitry V.
    University of Bath.
    Nonlinear gap modes and compactons in a lattice model for spin-orbit coupled exciton-polaritons in zigzag chains2019Ingår i: Journal of Physics Communications, ISSN 2399-6528, Vol. 3, nr 1, s. 1-17, artikel-id 015001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a system of generalized coupled Discrete Nonlinear Schrödinger (DNLS) equations, derived as a tight-binding model from the Gross-Pitaevskii-type equations describing a zigzag chain of weakly coupled condensates of exciton-polaritons with spin-orbit (TE-TM) coupling. We focus on the simplest case when the angles for the links in the zigzag chain are ±π/4 with respect to the chain axis, and the basis (Wannier) functions are cylindrically symmetric (zero orbital angular momenta). We analyze the properties of the fundamental nonlinear localized solutions, with particular interest in the discrete gap solitons appearing due to the simultaneous presence of spin–orbit coupling and zigzag geometry, opening a gap in the linear dispersion relation. In particular, their linear stability is analyzed. We also find that the linear dispersion relation becomes exactly flat at particular parameter values, and obtain corresponding compact solutions localized on two neighboring sites, with spin-up and spin-down parts π/2 out of phase at each site. The continuation of these compact modes into exponentially decaying gap modes for generic parameter values is studied numerically, and regions of stability are found to exist in the lower or upper half of the gap, depending on the type of gap modes.

  • 30.
    Gautam, Rekha
    et al.
    San Francisco State Univ, CA 94132 USA; Vanderbilt Univ, TN 37240 USA.
    Xiang, Yinxiao
    San Francisco State Univ, CA 94132 USA; Nankai Univ, Peoples R China; Nankai Univ, Peoples R China.
    Lamstein, Josh
    San Francisco State Univ, CA 94132 USA.
    Liang, Yi
    San Francisco State Univ, CA 94132 USA; Guangxi Univ, Peoples R China.
    Bezryadina, Anna
    San Francisco State Univ, CA 94132 USA; Calif State Univ Northridge, CA 91330 USA.
    Liang, Guo
    San Francisco State Univ, CA 94132 USA.
    Hansson, Tobias
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Quebec, Canada.
    Wetzel, Benjamin
    Univ Quebec, Canada; Univ Sussex, England.
    Preece, Daryl
    Univ Calif Irvine, CA USA.
    White, Adam
    San Francisco State Univ, CA 94132 USA.
    Silverman, Matthew
    San Francisco State Univ, CA 94132 USA.
    Kazarian, Susan
    San Francisco State Univ, CA 94132 USA.
    Xu, Jingjun
    Nankai Univ, Peoples R China.
    Morandotti, Roberto
    Univ Quebec, Canada; Univ Elect Sci and Tech China, Peoples R China; ITMO Univ, Russia.
    Chen, Zhigang
    San Francisco State Univ, CA 94132 USA; Nankai Univ, Peoples R China; Nankai Univ, Peoples R China.
    Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions2019Ingår i: Light: Science & Applications, ISSN 2095-5545, E-ISSN 2047-7538, Vol. 8, artikel-id 31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Osmotic conditions play an important role in the cell properties of human red blood cells (RBCs), which are crucial for the pathological analysis of some blood diseases such as malaria. Over the past decades, numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes. Here, we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions. Specifically, we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions, where the strength of the optical nonlinearity increases with osmotic pressure on the cells. This tunable nonlinearity is attributed to optical forces, particularly the forward-scattering and gradient forces. Interestingly, in aged blood samples (with lysed cells), a notably different nonlinear behavior is observed due to the presence of free hemoglobin. We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations. Our work on light self-guiding through scattering bio-soft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.

  • 31.
    Xu, Bin
    et al.
    Soochow Univ, Peoples R China; Univ Arkansas, AR 72701 USA; Univ Arkansas, AR 72701 USA.
    Hellman, Olle
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bellaiche, L.
    Univ Arkansas, AR 72701 USA.
    Order-disorder transition in the prototypical antiferroelectric PbZrO32019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 2, artikel-id 020102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The prototypical antiferroelectric PbZrO3 has several unsettled questions, such as the nature of the antiferroelectric transition, a possible intermediate phase, and the microscopic origin of the Pbam ground state. Using first-principles calculations, we show that no phonon becomes truly soft at the cubic-to-Pbam transition temperature, and the order-disorder character of this transition is clearly demonstrated based on molecular dynamics simulations and potential energy surfaces. The out-of-phase octahedral tilting is an important degree of freedom, which can collaborate with other phonon distortions and form a complex energy landscape with multiple minima Candidates of the possible intermediate phase are suggested based on the calculated kinetic barriers between energy minima, and the development of a first-principles-based effective Hamiltonian. The use of this latter scheme further reveals that specific bilinear interactions between local dipoles and octahedral tiltings play a major role in the formation of the Pbam ground state, which contrasts with most of the previous explanations.

  • 32.
    Pakhomova, Anna
    et al.
    DESY, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Gorelova, Liudmila
    St Petersburg State Univ, Russia.
    Krivovichev, Sergey S.
    St Petersburg State Univ, Russia; Russian Acad Sci, Russia.
    Belov, Maxim P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Penta- and hexa-coordinated beryllium and phosphorus in high-pressure modifications of CaBe2P2O82019Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, artikel-id 2800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe2P2O8, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe2P2O8 is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.

  • 33.
    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.

  • 34.
    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.

  • 35.
    Monteseguro, V
    et al.
    Univ Valencia, Spain; European Radiat Synchrotron Facil, France.
    Sans, J. A.
    Univ Politecn Valencia, Spain.
    Cuartero, V
    European Radiat Synchrotron Facil, France; Ctr Univ Def Zaragoza, Spain.
    Cova, F.
    European Radiat Synchrotron Facil, France.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Olovsson, Weine
    Linköpings universitet, Nationellt superdatorcentrum (NSC). Linköpings universitet, Tekniska fakulteten.
    Popescu, C.
    ALBA CELLS, Spain.
    Pascarelli, S.
    European Radiat Synchrotron Facil, France.
    Garbarino, G.
    European Radiat Synchrotron Facil, France.
    Jönsson, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Irifune, T.
    Ehime Univ, Japan; Tokyo Inst Technol, Japan.
    Errandonea, D.
    Univ Valencia, Spain.
    Phase stability and electronic structure of iridium metal at the megabar range2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 8940Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.

  • 36.
    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.

  • 37.
    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, 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.

  • 38.
    Hansson, Tobias
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Brescia, Italy.
    Parra-Rivas, P.
    Univ Libre Bruxelles, Belgium; Univ Leuven, Belgium.
    Bernard, M.
    Univ Brescia, Italy.
    Leo, F.
    Univ Libre Bruxelles, Belgium.
    Gelens, L.
    Univ Leuven, Belgium.
    Wabnitz, S.
    Univ Brescia, Italy; Sapienza Univ Roma, Italy.
    Quadratic cavity soliton optical frequency combs2019Ingår i: 2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO), IEEE , 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    We theoretically investigate the formation of frequency combs in a dispersive second-harmonic generation cavity system, and predict the existence of quadratic cavity solitons in the absence of a temporal walk-off. (C) 2019 The Author(s)

  • 39.
    da Cunha, Wiliam Ferreira
    et al.
    Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Quasiparticle description of transition metal dichalcogenide nanoribbons2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 3, artikel-id 035405Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An effective two-dimensional real-space model is developed to investigate the nature of charge distribution in nanoribbons of transition metal dichalcogenides. Our description is based on a lattice relaxation endowed tight-binding Hamiltonian with spin-orbit and Hubbard interactions, which is parameterized to describe molybdenum disulfide lattices. As our main finding, we observed that electron-phonon coupling induces the creation of quasiparticles such as polarons in the same fashion as observed in conducting polymers and graphene nanoribbons. These similarities suggest that the charge transport in transition metal dichalcogenides can also be mediated by quasiparticles, which is a fundamental aspect concerning the application of these structures in electronics. We determine a range of possible electron-phonon coupling that correctly describes the system and also the critical value where quasiparticle transport is present. Our findings may have profound consequences on the understanding of the transport mechanism of transition metal dichalcogenides nanoribbons.

  • 40.
    Mosyagin, Igor
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. NUST MISTS, Russia.
    Lugovskoy, A. V.
    NUST MISTS, Russia.
    Krasilnikov, O. M.
    NUST MISTS, Russia; NUST MISTS, Russia.
    Vekilov, Yu. Kh.
    NUST MISTS, Russia; NUST MISTS, Russia.
    Simak, Sergey
    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.
    Reply to the comment by M. Mazdziarz on the article "Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017) 20-30]2019Ingår i: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 235, s. 295-296Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Marcin Mazdziarz has published a comment on our recent paper by I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, Yu.Kh. Vekilov, S.I. Simak and L.A. Abrikosov titled "Ab initio calculations of pressure dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017)2030]. The author states that there are serious fundamental errors and flaws. In this reply we clarify all misunderstanding mentioned in the said comment. (C) 2018 Published by Elsevier B.V.

    Publikationen är tillgänglig i fulltext från 2020-06-19 15:55
  • 41.
    Almyras, Georgios
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Sangiovanni, Davide Giuseppe
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Semi-Empirical Force-Field Model For The Ti1-XAlXN (0 ≤ x ≤ 1) System2019Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 2, artikel-id 215Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a modified embedded atom method (MEAM) semi-empirical force-field model for the Ti1-xAlxN (0 x 1) alloy system. The MEAM parameters, determined via an adaptive simulated-annealing (ASA) minimization scheme, optimize the models predictions with respect to 0 K equilibrium volumes, elastic constants, cohesive energies, enthalpies of mixing, and point-defect formation energies, for a set of approximate to 40 elemental, binary, and ternary Ti-Al-N structures and configurations. Subsequently, the reliability of the model is thoroughly verified against known finite-temperature thermodynamic and kinetic properties of key binary Ti-N and Al-N phases, as well as properties of Ti1-xAlxN (0 amp;lt; x amp;lt; 1) alloys. The successful outcome of the validation underscores the transferability of our model, opening the way for large-scale molecular dynamics simulations of, e.g., phase evolution, interfacial processes, and mechanical response in Ti-Al-N-based alloys, superlattices, and nanostructures.

  • 42.
    Pereira Junior, Marcelo Lopes
    et al.
    Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Brasilia, Brazil.
    Stationary polaron properties in organic crystalline semiconductors2019Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, nr 5, s. 2727-2733Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Polarons play a crucial role in the charge transport mechanism when it comes to organic molecular crystals. The features of their underlying properties - mostly the ones that directly impact the yield of the net charge mobility - are still not completely understood. Here, a two-dimensional Holstein-Peierls model is employed to numerically describe the stationary polaron properties in organic semiconductors at a molecular scale. Our computational protocol yields model parameters that accurately characterize the formation and stability of polarons in ordered and disordered oligoacene-like crystals. The results show that the interplay between the intramolecular (Holstein) and intermolecular (Peierls) electron-lattice interactions critically impacts the polaron stability. Such an interplay can produce four distinct quasi-particle solutions: free-like electrons, metastable polarons, and small and large polarons. The latter governs the charge transport in organic crystalline semiconductors. Regarding disordered lattices, the model takes into account two modes of static disorder. Interestingly, the results show that intramolecular disorder is always unfavorable to the formation of polarons whereas intermolecular disorder may favor the polaron generation in regimes below a threshold for the electronic transfer integral strength.

  • 43.
    Gambino, Davide
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Structural and magnetic disorder in crystalline materials: a first principles study2019Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Disorder in crystalline materials can take different forms and originate from different sources. In particular, temperature introduces disorder in any kind of material. This can be observed as the appearance of vacant lattice sites in an otherwise perfect crystal, or as a random distribution of different elements on the same lattice in an alloy; at the same time, if the material is magnetic, temperature induces disorder also on the magnetic degrees of freedom. In this thesis, different levels of disorder associated to structure and magnetism are investigated by means of density functional theory and thermodynamic models.

    I start with diffusion of Ti vacancies in TiN, which is studied by means of nonequilibrium ab initio molecular dynamics using the color diffusion algorithm at different temperatures. The result is an Arrhenius behavior of Ti vacancy jump rates.

    A method to perform structural relaxations in magnetic materials in their hightemperature paramagnetic phase is then developed based on the disordered local moments approach in order to study vacancies, interstitial atoms, and combinations of defects in paramagnetic bcc Fe and B1 CrN, as well as the mixing enthalpy of bcc Fe1−xCrx random alloys. A correction to the energetics of every system due to the relaxation in the disordered magnetic state is observed in all cases.

    Not related to temperature and disorder, but very important for an accurate description of magnetic materials, is the choice of the exchange and correlation functional to be employed in the first principles calculations. We have investigated the performance of a recently developed meta-GGA functional, the strongly constrained and appropriately normed (SCAN) functional, in comparison with the more commonly used LDA and PBE on the ferromagnetic elemental solids bcc Fe, fcc Ni, and hcp Co, and SCAN it is found to give negligible improvements, if not a worsening, in the description of these materials.

    Finally, the coupling between vibrational and magnetic degrees of freedom is discussed by reviewing the literature and proposing an investigation of the influence of vibrations on longitudinal spin fluctuations. These excitations are here studied by means of thermodynamic models based on Landau expansion of the energy in even powers of the magnitude of the local magnetic moments. We find that vibrational and magnetic disorder alter the energy landscapes as a function of moment size also in bcc Fe, which is often considered a Heisenberg system, inducing a more itinerant electron behavior.

    Delarbeten
    1. Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN
    Öppna denna publikation i ny flik eller fönster >>Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN
    2017 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 10, artikel-id 104306Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    We use the color diffusion (CD) algorithm in nonequilibrium (accelerated) ab initio molecular dynamics simulations to determine Ti monovacancy jump frequencies in NaCl-structure titanium nitride (TiN), at temperatures ranging from 2200 to 3000 K. Our results showthat theCDmethod extended beyond the linear-fitting rate-versus-force regime [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)] can efficiently determine metal vacancy migration rates in TiN, despite the low mobilities of lattice defects in this type of ceramic compound. We propose a computational method based on gamma-distribution statistics, which provides unambiguous definition of nonequilibrium and equilibrium (extrapolated) vacancy jump rates with corresponding statistical uncertainties. The acceleration-factor achieved in our implementation of nonequilibrium molecular dynamics increases dramatically for decreasing temperatures from 500 for T close to the melting point T-m, up to 33 000 for T approximate to 0.7 T-m

    Ort, förlag, år, upplaga, sidor
    AMER PHYSICAL SOC, 2017
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-141712 (URN)10.1103/PhysRevB.96.104306 (DOI)000411076000005 ()
    Anmärkning

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL [10-0026]; Swedish Research Council (VR) [621-2011-4417, 2015-04391, 330-2014-6336]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials [MatLiU 2009-00971]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Marie Sklodowska Curie Actions [INCA 600398]; Swedish Foundation for Strategic Research; Stiftelsen Olle Engkvist Byggmastare

    Tillgänglig från: 2017-10-05 Skapad: 2017-10-05 Senast uppdaterad: 2019-06-28
    2. Lattice relaxations in disordered Fe-based materials in the paramagnetic state from first principles
    Öppna denna publikation i ny flik eller fönster >>Lattice relaxations in disordered Fe-based materials in the paramagnetic state from first principles
    2018 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 6, artikel-id 064105Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The first-principles calculation of many material properties, in particular related to defects and disorder, starts with the relaxation of the atomic positions of the system under investigation. This procedure is routine for nonmagnetic and magnetically ordered materials. However, when it comes to magnetically disordered systems, in particular the paramagnetic phase of magnetic materials, it is not clear how the relaxation procedure should be performed or which geometry should be used. Here we propose a method for the structural relaxation of magnetic materials in the paramagnetic regime, in an adiabatic fast-magnetism approximation within the disordered local moment (DLM) picture in the framework of density functional theory. The method is straightforward to implement using any ab initio code that allows for structural relaxations. We illustrate the importance of considering the disordered magnetic state during lattice relaxations by calculating formation energies and geometries for an Fe vacancy and C insterstitial atom in body-centered cubic (bcc) Fe as well as bcc Fe1-xCrx random alloys in the paramagnetic state. In the vacancy case, the nearest neighbors to the vacancy relax toward the vacancy of 0.14 angstrom (-5% of the ideal bcc nearest-neighbor distance), which is twice as large as the relaxation in the ferromagnetic case. The vacancy formation energy calculated in the DLM state on these positions is 1.60 eV, which corresponds to a reduction of about 0.1 eV compared to the formation energy calculated using DLM but on ferromagnetic-relaxed positions. The carbon interstitial formation energy is found to be 0.41 eV when the DLM relaxed positions are used, as compared to 0.59 eV when the FM-relaxed positions are employed. For bcc Fe0.5Cr0.5 alloys, the mixing enthalpy is reduced by 5 meV/atom, or about 10%, when the DLM state relaxation is considered, as compared to positions relaxed in the ferromagnetic state.

    Ort, förlag, år, upplaga, sidor
    AMER PHYSICAL SOC, 2018
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-151199 (URN)10.1103/PhysRevB.98.064105 (DOI)000443139600004 ()
    Anmärkning

    Funding Agencies|Swedish Research Council (VR) [2014-6336]; Marie Sklodowska Curie Actions, Cofund [INCA 600398]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFOMatLiU) [2009 00971]; Swedish Foundation for Strategic Research

    Tillgänglig från: 2018-09-13 Skapad: 2018-09-13 Senast uppdaterad: 2019-05-14
    3. Assessing the SCAN functional for itinerant electron ferromagnets
    Öppna denna publikation i ny flik eller fönster >>Assessing the SCAN functional for itinerant electron ferromagnets
    Visa övriga...
    2018 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 9, artikel-id 094413Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Density functional theory is a standard model for condensed-matter theory and computational material science. The accuracy of density functional theory is limited by the accuracy of the employed approximation to the exchange-correlation functional. Recently, the so-called strongly constrained appropriately normed (SCAN) [Sun, Ruzsinszky, and Perdew, Phys. Rev. Lett. 115, 036402 (2015)] functional has received a lot of attention due to promising results for covalent, metallic, ionic, as well as hydrogen- and van der Waals-bonded systems alike. In this work, we focus on assessing the performance of the SCAN functional for itinerant magnets by calculating basic structural and magnetic properties of the transition metals Fe, Co, and Ni. We find that although structural properties of bcc-Fe seem to be in good agreement with experiment, SCAN performs worse than standard local and semilocal functionals for fcc-Ni and hcp-Co. In all three cases, the magnetic moment is significantly overestimated by SCAN, and the 3d states are shifted to lower energies, as compared to experiments.

    Ort, förlag, år, upplaga, sidor
    AMER PHYSICAL SOC, 2018
    Nationell ämneskategori
    Teoretisk kemi
    Identifikatorer
    urn:nbn:se:liu:diva-151640 (URN)10.1103/PhysRevB.98.094413 (DOI)000444348500004 ()
    Anmärkning

    Funding Agencies|Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) through the International Career Grant [20146336]; Marie Sklodowska CurieActions, Cofund, Project [INCA 600398]; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 6 program; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; competence center FunMat-II - Vinnova [201605156]; Russian Science Foundation [18-12-00492]

    Tillgänglig från: 2018-09-27 Skapad: 2018-09-27 Senast uppdaterad: 2019-05-14
  • 44.
    Sangiovanni, Davide
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Ruhr Univ Bochum, Germany.
    Klarbring, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Smirnova, D.
    Ruhr Univ Bochum, Germany; Russian Acad Sci, Russia.
    Skripnyak, Natalia
    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.
    Mrovec, M.
    Ruhr Univ Bochum, Germany.
    Simak, Sergey
    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.
    Superioniclike Diffusion in an Elemental Crystal: bcc Titanium2019Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, nr 10, artikel-id 105501Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent theoretical investigations [A. B. Belonoshko et aL Nat. Geosci. 10, 312 (2017)] revealed the occurrence of the concerted migration of several atoms in bcc Fe at inner-core temperatures and pressures. Here, we combine first-principles and semiempirical atomistic simulations to show that a diffusion mechanism analogous to the one predicted for bcc iron at extreme conditions is also operative and of relevance for the high-temperature bcc phase of pure Ti at ambient pressure. The mechanism entails a rapid collective movement of numerous (from two to dozens) neighbors along tangled closed-loop paths in defect-free crystal regions. We argue that this phenomenon closely resembles the diffusion behavior of superionics and liquid metals. Furthermore, we suggest that concerted migration is the atomistic manifestation of vanishingly small co-mode phonon frequencies previously detected via neutron scattering and the mechanism underlying anomalously large and markedly non-Arrhenius self-diffusivities characteristic of bcc Ti.

  • 45.
    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.

    Publikationen är tillgänglig i fulltext från 2020-10-26 15:00
  • 46.
    Filippov, Stanislav
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Stockholm Univ, Sweden.
    Klarbring, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Temperature-induced phase transition and Li self-diffusion in Li2C2: A first-principles study2019Ingår i: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, nr 2, artikel-id 023602Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lithium carbide, Li2C2, is a fascinating material that combines strong covalent and weak ionic bonding resulting in a wide range of unusual properties. The mechanism of its phase transition from the ground-state orthorhombic (Immm) to the high-temperature cubic (Fm (3) over barm) crystal structure is not well understood and here we elucidate it with help of first-principles calculations. We show that stabilization of the cubic phase is a result of a temperature-induced disorientation of the C-C dumbbells and their further thermal rotations. Due to these rotations rather large deviatoric stress, which is associated with the dumbbell alignment along one of the crystallographic axes, averages out making the cubic structure mechanically stable. At high temperature we observe a type-II superionic transition to a state of high Li self-diffusion involving collective ionic motion mediated by the formation of Frenkel pairs.

  • 47.
    Pilemalm, Robert
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergei
    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.
    The Effect of Point Defects on the Electronic Density of States of ScMN2-Type (M = V, Nb, Ta) Phases2019Ingår i: Condensed Matter, ISSN 2410-3896, Vol. 4, nr 3, artikel-id 70Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb. They are narrow-bandgap semiconductors with potentially interesting thermoelectric properties. Point defects such as dopants and vacancies largely affect these properties, motivating the need to investigate these effects. In particular, asymmetric peak features in the density of states (DOS) close to the highest occupied state is expected to increase the Seebeck coefficient. Here, we used first principles calculations to study the effects of one vacancy or one C, O, or F dopant on the DOS of the ScMN2 phases. We used density functional theory to calculate formation energy and the density of states when a point defect is introduced in the structures. In the DOS, asymmetric peak features close to the highest occupied state were found as a result of having a vacancy in all three phases. Furthermore, one C dopant in ScTaN2, ScNbN2, and ScVN2 implies a shift of the highest occupied state into the valence band, while one O or F dopant causes a shift of the highest occupied state into the conduction band.

  • 48.
    Palonen, H.
    et al.
    Uppsala Univ, Sweden.
    Mukhamedov, B. O.
    Natl Univ Sci and Technol MISIS, Russia.
    Ponomareva, A. V.
    Natl Univ Sci and Technol MISIS, Russia.
    Palsson, G. K.
    Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Hjorvarsson, B.
    Uppsala Univ, Sweden.
    The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice2019Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, nr 1, artikel-id 012406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing.

  • 49.
    Ekholm, Marcus
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Univ Bayreuth, Germany.
    Schoenleber, A.
    Univ Bayreuth, Germany.
    van Smaalen, S.
    Univ Bayreuth, Germany.
    The role of magnetic order in VOCl2019Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, nr 32, artikel-id 325502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    VOCl and other transition metal oxychlorides are candidate materials for next-generation rechargeable batteries. We have investigated the influence of the underlying magnetic order on the crystallographic and electronic structure by means of density functional theory. Our study shows that antiferromagnetic ordering explains the observed low-temperature monoclinic distortion of the lattice, which leads to a decreased distance between antiferromagnetically coupled V-V nearest neighbors. We also show that the existence of a local magnetic moment removes the previously suggested degeneracy of the occupied levels, in agreement with experiments. To describe the electronic structure, it turns out crucial to take the correct magnetic ordering into account, especially at elevated temperature.

  • 50.
    Ning, Weihua
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten. Nanjing Tech Univ, Peoples R China.
    Zhao, Xin-Gang
    Jilin Univ, Peoples R China.
    Klarbring, Johan
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Bai, Sai
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Ji, Fuxiang
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Wang, Feng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Simak, Sergey
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Tao, Youtian
    Nanjing Tech Univ, Peoples R China.
    Ren, Xiao-Ming
    Nanjing Tech Univ, Peoples R China.
    Zhang, Lijun
    Jilin Univ, Peoples R China.
    Huang, Wei
    Nanjing Tech Univ, Peoples R China.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten. Natl Univ Sci and Technol MISIS, Russia.
    Gao, Feng
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biomolekylär och Organisk Elektronik. Linköpings universitet, Tekniska fakulteten.
    Thermochromic Lead-Free Halide Double Perovskites2019Ingår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, nr 10, artikel-id 1807375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lead-free halide double perovskites with diverse electronic structures and optical responses, as well as superior material stability show great promise for a range of optoelectronic applications. However, their large bandgaps limit their applications in the visible light range such as solar cells. In this work, an efficient temperature-derived bandgap modulation, that is, an exotic fully reversible thermochromism in both single crystals and thin films of Cs2AgBiBr6 double perovskites is demonstrated. Along with the thermochromism, temperature-dependent changes in the bond lengths of Ag Symbol of the Klingon Empire Br (R-Ag Symbol of the Klingon Empire Br) and Bi Symbol of the Klingon Empire Br (R-Bi Symbol of the Klingon Empire Br) are observed. The first-principle molecular dynamics simulations reveal substantial anharmonic fluctuations of the R-Ag Symbol of the Klingon Empire Br and R-Bi Symbol of the Klingon Empire Br at high temperatures. The synergy of anharmonic fluctuations and associated electron-phonon coupling, and the peculiar spin-orbit coupling effect, is responsible for the thermochromism. In addition, the intrinsic bandgap of Cs2AgBiBr6 shows negligible changes after repeated heating/cooling cycles under ambient conditions, indicating excellent thermal and environmental stability. This work demonstrates a stable thermochromic lead-free double perovskite that has great potential in the applications of smart windows and temperature sensors. Moreover, the findings on the structure modulation-induced bandgap narrowing of Cs2AgBiBr6 provide new insights for the further development of optoelectronic devices based on the lead-free halide double perovskites.

    Publikationen är tillgänglig i fulltext från 2020-01-20 15:10
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