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  • 1.
    Baldwin, William J.
    et al.
    Univ Cambridge, England.
    Liang, Xia
    Imperial Coll London, England.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Imperial Coll London, England.
    Dubajic, Milos
    Univ Cambridge, England.
    Dell Angelo, David
    Unita Cagliari, Italy.
    Sutton, Christopher
    Univ South Carolina, SC 29208 USA.
    Caddeo, Claudia
    Unita Cagliari, Italy.
    Stranks, Samuel D.
    Univ Cambridge, England.
    Mattoni, Alessandro
    Unita Cagliari, Italy.
    Walsh, Aron
    Imperial Coll London, England.
    Csanyi, Gabor
    Univ Cambridge, England.
    Dynamic Local Structure in Caesium Lead Iodide: Spatial Correlation and Transient Domains2023In: Small, ISSN 1613-6810, E-ISSN 1613-6829Article in journal (Refereed)
    Abstract [en]

    Metal halide perovskites are multifunctional semiconductors with tunable structures and properties. They are highly dynamic crystals with complex octahedral tilting patterns and strongly anharmonic atomic behavior. In the higher temperature, higher symmetry phases of these materials, several complex structural features are observed. The local structure can differ greatly from the average structure and there is evidence that dynamic 2D structures of correlated octahedral motion form. An understanding of the underlying complex atomistic dynamics is, however, still lacking. In this work, the local structure of the inorganic perovskite CsPbI3 is investigated using a new machine learning force field based on the atomic cluster expansion framework. Through analysis of the temporal and spatial correlation observed during large-scale simulations, it is revealed that the low frequency motion of octahedral tilts implies a double-well effective potential landscape, even well into the cubic phase. Moreover, dynamic local regions of lower symmetry are present within both higher symmetry phases. These regions are planar and the length and timescales of the motion are reported. Finally, the spatial arrangement of these features and their interactions are investigated and visualized, providing a comprehensive picture of local structure in the higher symmetry phases.

  • 2.
    Cohen, Adi
    et al.
    Weizmann Inst Sci, Israel.
    Brenner, Thomas M.
    Weizmann Inst Sci, Israel.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Sharma, Rituraj
    Weizmann Inst Sci, Israel.
    Fabini, Douglas H.
    Max Planck Inst Solid State Res, Germany.
    Korobko, Roman
    Weizmann Inst Sci, Israel.
    Nayak, Pabitra K.
    Tata Inst Fundamental Res, India.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Yaffe, Omer
    Weizmann Inst Sci, Israel.
    Diverging Expressions of Anharmonicity in Halide Perovskites2022In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 14, article id 2107932Article in journal (Refereed)
    Abstract [en]

    Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below approximate to 37 K.

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  • 3.
    Ekström, Erik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Le Febvrier, Arnaud
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Bourgeois, F.
    Univ Technol Blois, France.
    Lundqvist, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Caballero-Calero, O.
    CEI UAM, Spain.
    Martin-Gonzalez, M. S.
    CEI UAM, Spain.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Paul, Biplab
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    The effects of microstructure, Nb content and secondary Ruddlesden-Popper phase on thermoelectric properties in perovskite CaMn1-xNbxO3 (x=0-0.10) thin films2020In: RSC Advances, E-ISSN 2046-2069, RSC ADVANCES, Vol. 10, no 13, p. 7918-7926Article in journal (Refereed)
    Abstract [en]

    CaMn1-xNbxO3 (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn1-x,Nb-x)O thin films were deposited on 11 & x304;00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn1-xNbxO3 films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn1-xNbx)O to orthorhombic during post-deposition annealing at 700 degrees C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO3 showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden-Popper (R-P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn1-xNbxO3. The electrical resistivity and Seebeck coefficient of the pure CaMnO3 film were measured to 2.7 omega cm and -270 mu V K-1 at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 omega cm and -145 mu V K-1 for x = 0.05. Yielding a power factor of 21.5 mu W K-2 m(-1) near room temperature, nearly eight times higher than for pure CaMnO3 (2.8 mu W K-2 m(-1)). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R-P phase. The thermal conductivity of the CaMn1-xNbxO3 films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m(-1) K-1. The low thermal conductivity is attributed to grain boundary scattering and the secondary R-P phase.

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  • 4.
    Filippov, Stanislav
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Stockholm Univ, Sweden.
    Grinderslev, Jakob B.
    Aarhus Univ, Denmark.
    Andersson, Mikael S.
    Chalmers Univ Technol, Sweden.
    Armstrong, Jeff
    Rutherford Appleton Lab, England.
    Karlsson, Maths
    Chalmers Univ Technol, Sweden.
    Jensen, Torben R.
    Aarhus Univ, Denmark.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Analysis of Dihydrogen Bonding in Ammonium Borohydride2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 47, p. 28631-28639Article in journal (Refereed)
    Abstract [en]

    The structural and vibrational properties of ammonium borohydride, NH4BH4, have been examined by first-principles density functional theory (DFT) calculations and inelastic neutron scattering (INS). The H disordered crystal structure of NH4BH4 is composed of the tetrahedral complex ions NH4+ and BH4-, which are arranged as in the fcc NaCl structure and linked by intermolecular dihydrogen bonding. Upon cooling, the INS spectra revealed a structural transition between 45 and 40 K. The reversible transition occurs upon heating between 46 and 49 K. In the low-temperature form reorientational dynamics are frozen. The libration modes for BH4- and NH4+ are near 300 and 200 cm(-1), respectively. Upon entering the fcc high-temperature form, NH4+ ions attain fast reorientational dynamics, as indicated in the disappearance of the NH4+ libration band, whereas BH4- ions become significantly mobile only at temperatures above 100 K. The vibrational behavior of BH4- ions in NH4BH4 compares well to the heavier alkali metal borohydrides, NaBH4-CsBH4. DFT calculations revealed a nondirectional nature of the dihydrogen bonding in NH4BH4 with only weak tendency for long-range order. Different rotational configurations of complex ions appear quasi-degenerate, which is reminiscent of glasses.

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  • 5.
    Filippov, Stanislav
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Stockholm Univ, Sweden.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Temperature-induced phase transition and Li self-diffusion in Li2C2: A first-principles study2019In: Physical Review Materials, E-ISSN 2475-9953, Vol. 3, no 2, article id 023602Article in journal (Refereed)
    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.

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  • 6.
    Gambino, Davide
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Imperial Coll London, England.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Phase stability of Fe from first principles: Atomistic spin dynamics coupled with ab initio molecular dynamics simulations and thermodynamic integration2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 1, article id 014102Article in journal (Refereed)
    Abstract [en]

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

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  • 7.
    Ji, Fuxiang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Huang, Yuqing
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Kobera, Libor
    Czech Acad Sci, Czech Republic.
    Xie, Fangyan
    Sun Yat Sen Univ, Peoples R China.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abbrent, Sabina
    Czech Acad Sci, Czech Republic.
    Brus, Jiri
    Czech Acad Sci, Czech Republic.
    Yin, Chunyang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci & Technol MISIS, Russia.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Near-Infrared Light-Responsive Cu-Doped Cs2AgBiBr62020In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 30, no 51, article id 2005521Article in journal (Refereed)
    Abstract [en]

    Lead-free halide double perovskites (A(2)B(I)B(III)X(6)) with attractive optical and electronic features are considered to be a promising candidate to overcome the toxicity and stability issues of lead halide perovskites (APbX(3)). However, their poor absorption profiles limit device performance. Here the absorption band edge of Cs(2)AgBiBr(6)double perovskite to the near-infrared range is significantly broadened by developing doped double perovskites, Cs-2(Ag:Cu)BiBr6. The partial replacement of Ag ions by Cu ions in the crystal lattice is confirmed by the X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (ssNMR) measurements. Cu doping barely affects the bandgap of Cs2AgBiBr6; instead it introduces subbandgap states with strong absorption to the near-infrared range. More interestingly, the near-infrared absorption can generate band carriers upon excitation, as indicated by the photoconductivity measurement. This work sheds new light on the absorption modulation of halide double perovskites for future efficient optoelectronic devices.

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  • 8.
    Ji, Fuxiang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ning, Weihua
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Linqin
    KTH Royal Inst Technol, Sweden.
    Yin, Chunyang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Mendoza Figueroa, José Silvestre
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Christensen, Christian Kolle
    DESY, Germany.
    Etter, Martin
    DESY, Germany.
    Ederth, Thomas
    Linköping University, Department of Physics, Chemistry and Biology, Biophysics and bioengineering. Linköping University, Faculty of Science & Engineering.
    Sun, Licheng
    KTH Royal Inst Technol, Sweden; Dalian Univ Technol, Peoples R China.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Lead-Free Halide Double Perovskite Cs2AgBiBr6with Decreased Band Gap2020In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 59, no 35, p. 15191-15194Article in journal (Refereed)
    Abstract [en]

    Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs(2)AgBiBr(6)under ambient conditions. The band-gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag-Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band-gap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable band gaps for optoelectronic applications.

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  • 9.
    Ji, Fuxiang
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Zhang, Bin
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Wang, Linqin
    School of Science Westlake University Hangzhou, P.R. China.
    Miao, Xiaohe
    Westlake University Hangzhou, P.R. China.
    Ning, Weihua
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Soochow University Suzhou, P. R. China.
    Zhang, Muyi
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Cai, Xinyi
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Bakhit, Babak
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ren, Xiaoming
    State Key Laboratory of Materials‐Oriented Chemical Engineering and College of Chemistry and Molecular Engineering Nanjing Tech University Nanjing, P.R. China.
    Sun, Licheng
    Center of Artificial Photosynthesis for Solar Fuels, School of Science Westlake University Hangzhou,P.R. China.
    Fahlman, Mats
    Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina A
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials.
    Chen, Weimin
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials.
    Simak, Sergei I
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala University Uppsala SE‐75120 Sweden.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl62023In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, article id 2301102Article in journal (Refereed)
    Abstract [en]

    Lead-free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light-yellow to black over a temperature range of 10 to 423 K is investigated. First-principles, density functional theory (DFT)-based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron–phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK−1 based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group-IV, III–V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials.

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  • 10. Order onlineBuy this publication >>
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    A First-Principles Study of Highly Anharmonic and Dynamically Disordered Solids2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is a first-principles theoretical investigation of solid materials with high degrees of anharmonicity. These are systems where the dynamics of the constituent atoms is too complex to be well-described by a set of uncoupled harmonic oscillators. While theoretical studies of such systems pose a significant challenge, they are under increasing demand due to the prevalence of these sytems in next-generation technological applications. Indeed, very anharmonic systems are ubiquitous in envisioned materials for future solid-state batteries and fuel-cells, thermoelectrics and optoelectronics. In some of these cases, the anharmonicity is a “side-effect” that simply has to be dealt with in order to accurately model certain properties, while in other cases the anharmonicity is the origin of the high-performance of the material.

    There are two main parts to the thesis: The first is on materials with perovskite-related structures. This is a very large class of materials, members of which are typically highly anharmonic, not least in relation to a series of complex phase transformations between different structural modifications. In the thesis, I have studied a specific class of such phase-transformations that relate to tilting of the framework of octahedra that make up the structure. The oxide CaMnO3 and a set of inorganic halide perovskites were taken as model systems. The results shed some light on the experimentally observed differences between the local and average atomic structure in these systems. I have further studied Cs2AgBiBr6, a member of the so-called lead-free halide double perovskites. I rationalized its temperature induced phase transformation and found high degrees of anharmonicity and ultra-low thermal conductivity. Finally, I studied the influence of nuclear quantum effects, which are often ignored in computational modelling, on the structure and bonding in the hybrid organic-inorganic lead-halide perovskite, CH3NH3PbI3.

    The second part of the thesis deals with theoretical studies of the phase stability of dynamically disordered solids. These are solids which have some sort of time-averaged long-range order, characteristic of a crystalline solid, but where the anharmonicity is so strong that the basic concept of an equilibrium atomic position cannot be statically assigned to all atoms. Examples include certain solids with very fast ionic conduction, so called superionics, and solids with rotating molecular units. This absence of equilibrium atomic positions makes many standard computational techniques to evaluate phase-stability inapplicable. I outline a method to deal with this issue, which is based on a stress-strain thermodynamic integration on a deformation path from an ordered variant to the dynamically disordered phase itself. I apply the method to study the phase stability of the high-temperature δ-phase of Bi2O3, which is the fastest know solid oxide ion conductor, and to Li2C2, whose high temperature cubic phase contains rotating C2 dimers.

    The thesis exemplifies the need to go beyond many of the standard approximations used in first-principles computational materials science if accurate theoretical predictions are to be made. This is true, in particular, for many emerging material classes in the field of energy materials.

    List of papers
    1. Nature of the octahedral tilting phase transitions in perovskites: A case study of CaMnO3
    Open this publication in new window or tab >>Nature of the octahedral tilting phase transitions in perovskites: A case study of CaMnO3
    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 2, article id 024108Article in journal (Refereed) Published
    Abstract [en]

    The temperature-induced antiferrodistortive (AFD) structural phase transitions in CaMnO3, a typical perovskite oxide, are studied using first-principles density functional theory calculations. These transitions are caused by tilting of the MnO6 octahedra that are related to unstable phonon modes in the high-symmetry cubic perovskite phase. Transitions due to octahedral tilting in perovskites normally are believed to fit into the standard soft-mode picture of displacive phase transitions. We calculate phonon-dispersion relations and potential-energy landscapes as functions of the unstable phonon modes and argue based on the results that the phase transitions are better described as being of order-disorder type. This means that the cubic phase emerges as a dynamical average when the system hops between local minima on the potential-energy surface. We then perform ab initio molecular dynamics simulations and find explicit evidence of the order-disorder dynamics in the system. Our conclusions are expected to be valid for other perovskite oxides, and we finally suggest how to predict the nature (displacive or order-disorder) of the AFD phase transitions in any perovskite system.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-144883 (URN)10.1103/PhysRevB.97.024108 (DOI)000423118400003 ()
    Note

    Funding Agencies|Swedish Research Council (VR) [2014-4750]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; CeNano at Linkoping University

    Available from: 2018-02-09 Created: 2018-02-09 Last updated: 2020-05-06
    2. Low-energy paths for octahedral tilting in inorganic halide perovskites
    Open this publication in new window or tab >>Low-energy paths for octahedral tilting in inorganic halide perovskites
    2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104105Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2019
    National Category
    Other Physics Topics
    Identifiers
    urn:nbn:se:liu:diva-156096 (URN)10.1103/PhysRevB.99.104105 (DOI)000461955500001 ()
    Note

    Funding Agencies|Swedish Research Council (VR) [2014-4750]; Centre in Nano Science and Nano Technology (CeNano) at Linkoping University

    Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2020-05-06
    3. Finite-temperature lattice dynamics and superionic transition in ceria from first principles
    Open this publication in new window or tab >>Finite-temperature lattice dynamics and superionic transition in ceria from first principles
    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104309Article in journal (Refereed) Published
    Abstract [en]

    Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B-1u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the E-u mode prevents the B-1u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-147104 (URN)10.1103/PhysRevB.97.104309 (DOI)000427982100003 ()
    Note

    Funding Agencies|Swedish Research Council [2014-4750, 2014-5993]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

    Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2020-05-06
    4. Phase Stability of Dynamically Disordered Solids from First Principles
    Open this publication in new window or tab >>Phase Stability of Dynamically Disordered Solids from First Principles
    2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 22, article id 225702Article in journal (Refereed) Published
    Abstract [en]

    Theoretical studies of phase stability in solid materials with dynamic disorder are challenging due to the failure of the standard picture of atoms vibrating around fixed equilibrium positions. Dynamically disordered solid materials show immense potential in applications. In particular, superionic conductors, where the disorder results in exceptionally high ionic conductivity, are very promising as solid state electrolytes in batteries and fuel cells. The biggest obstacle in living up to this potential is the limited stability of the dynamically disordered phases. Here, we outline a method to obtain the free energy of a dynamically disordered solid. It is based on a stress-strain thermodynamic integration on a deformation path between a mechanically stable ordered variant of the disordered phase, and the dynamically disordered phase itself. We show that the large entropy contribution associated with the dynamic disorder is captured in the behavior of the stress along the deformation path. We apply the method to Bi2O3, whose superionic delta phase is the fastest known solid oxide ion conductor. We accurately reproduce the experimental transition enthalpy and the critical temperature of the phase transition from the low temperature ground state a phase to the superionic d phase. The method can be used for a first-principles description of the phase stability of superionic conductors and other materials with dynamic disorder, when the disordered phase can be connected to a stable phase through a continuous deformation path.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Inorganic Chemistry
    Identifiers
    urn:nbn:se:liu:diva-153532 (URN)10.1103/PhysRevLett.121.225702 (DOI)000451581600011 ()30547633 (PubMedID)
    Note

    Funding Agencies|Swedish Research Council (VR) [2014-4750]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

    Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2020-05-06
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  • 11.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Low-energy paths for octahedral tilting in inorganic halide perovskites2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104105Article in journal (Refereed)
    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.

    Download full text (pdf)
    fulltext
  • 12.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci & Technol NUST MISIS, Russia.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Anharmonicity and Ultralow Thermal Conductivity in Lead-Free Halide Double Perovskites2020In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 125, no 4, article id 045701Article in journal (Refereed)
    Abstract [en]

    The lead-free halide double perovskite class of materials offers a promising venue for resolving issues related to toxicity of Pb and long-term stability of the lead-containing halide perovskites. We present a first-principles study of the lattice vibrations in Cs2AgBiBr6, the prototypical compound in this class and show that the lattice dynamics of Cs2AgBiBr6 is highly anharmonic, largely in regards to tilting of AgBr6 and BiBr6 octahedra. Using an energy- and temperature-dependent phonon spectral function, we then show how the experimentally observed cubic-to-tetragonal phase transformation is caused by the collapse of a soft phonon branch. We finally reveal that the softness and anharmonicity of Cs2AgBiBr6 yield an ultralow thermal conductivity, unexpected of high-symmetry cubic structures.

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  • 13.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nature of the octahedral tilting phase transitions in perovskites: A case study of CaMnO32018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 2, article id 024108Article in journal (Refereed)
    Abstract [en]

    The temperature-induced antiferrodistortive (AFD) structural phase transitions in CaMnO3, a typical perovskite oxide, are studied using first-principles density functional theory calculations. These transitions are caused by tilting of the MnO6 octahedra that are related to unstable phonon modes in the high-symmetry cubic perovskite phase. Transitions due to octahedral tilting in perovskites normally are believed to fit into the standard soft-mode picture of displacive phase transitions. We calculate phonon-dispersion relations and potential-energy landscapes as functions of the unstable phonon modes and argue based on the results that the phase transitions are better described as being of order-disorder type. This means that the cubic phase emerges as a dynamical average when the system hops between local minima on the potential-energy surface. We then perform ab initio molecular dynamics simulations and find explicit evidence of the order-disorder dynamics in the system. Our conclusions are expected to be valid for other perovskite oxides, and we finally suggest how to predict the nature (displacive or order-disorder) of the AFD phase transitions in any perovskite system.

    Download full text (pdf)
    fulltext
  • 14.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Phase Stability of Dynamically Disordered Solids from First Principles2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 22, article id 225702Article in journal (Refereed)
    Abstract [en]

    Theoretical studies of phase stability in solid materials with dynamic disorder are challenging due to the failure of the standard picture of atoms vibrating around fixed equilibrium positions. Dynamically disordered solid materials show immense potential in applications. In particular, superionic conductors, where the disorder results in exceptionally high ionic conductivity, are very promising as solid state electrolytes in batteries and fuel cells. The biggest obstacle in living up to this potential is the limited stability of the dynamically disordered phases. Here, we outline a method to obtain the free energy of a dynamically disordered solid. It is based on a stress-strain thermodynamic integration on a deformation path between a mechanically stable ordered variant of the disordered phase, and the dynamically disordered phase itself. We show that the large entropy contribution associated with the dynamic disorder is captured in the behavior of the stress along the deformation path. We apply the method to Bi2O3, whose superionic delta phase is the fastest known solid oxide ion conductor. We accurately reproduce the experimental transition enthalpy and the critical temperature of the phase transition from the low temperature ground state a phase to the superionic d phase. The method can be used for a first-principles description of the phase stability of superionic conductors and other materials with dynamic disorder, when the disordered phase can be connected to a stable phase through a continuous deformation path.

  • 15.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Singh, Utkarsh
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Electronic structure of the magnetic halide double perovskites Cs-2(Ag, Na)FeCl6 from first principles2023In: Physical Review Materials, E-ISSN 2475-9953, Vol. 7, no 4, article id 044605Article in journal (Refereed)
    Abstract [en]

    A family of magnetic halide double perovskites (HDPs) have recently attracted attention due to their potential to broaden application areas of halide double perovskites into, e.g., spintronics. Up to date the theoretical modeling of these systems have relied on primitive approximations to the density functional theory (DFT). In this paper, we study structural, electronic and magnetic properties of the Fe3+-containing HDPs Cs2AgFeCl6 and Cs2NaFeCl6 using a combination of more advanced DFT-based methods, including DFT + U, hybrid-DFT, and treatments of various magnetic states. We examine the effect of varying the effective Hubbard parameter, U-eff, in DFT + U and the mixing-parameter, alpha, in hybrid DFT on the electronic structure and structural properties. Our results reveal a set of localized Fe(d) states that are highly sensitive to these parameters. Cs2AgFeCl6 and Cs2NaFeCl6 are both antiferromagnets with Neel temperatures well below room temperature and are thus in their paramagnetic (PM) state at the external conditions relevant to most applications. Therefore, we have examined the effect of disordered magnetism on the electronic structure of these systems and find that while Cs2NaFeCl6 is largely unaffected, Cs2AgFeCl6 shows significant renormalization of its electronic band structure.

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  • 16.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Skorodumova, Natalia V.
    KTH Royal Inst Technol, Sweden; Uppsala Univ, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Finite-temperature lattice dynamics and superionic transition in ceria from first principles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104309Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B-1u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the E-u mode prevents the B-1u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

  • 17.
    Klarbring, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Vekilova, Olga Yu.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Nilsson, Johan O.
    KTH Royal Institute Technology, Sweden.
    Skorodumova, Natalia V.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ionic conductivity in Sm-doped ceria from first-principles non-equilibrium molecular dynamics2016In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 296, p. 47-53Article in journal (Refereed)
    Abstract [en]

    Sm-doped ceria is a prospective electrolyte material for intermediate-temperature solid-oxide fuel cells (IT-SOFC). Equilibrium ab initio molecular dynamics (AIMD) studies of oxygen ion diffusion in this material are currently impractical due to the rareness of diffusive events on the accessible timescale. To overcome this issue we have performed ab initio non-equilibrium molecular dynamics calculations of Sm-doped ceria using the color diffusion algorithm. Applying an external force field we have been able to increase the frequency of diffusive events over the simulation time, while keeping the physical mechanism of diffusion intact. We have investigated the temperature dependence of the maximum strength of the applied external field that could be used while maintaining the response of the system in a linear regime. This allows one to obtain the diffusivity at zero field. The bulk ionic conductivity has been calculated and found to match the experimental data well. We have also compared the description of the diffusion process by our method to previous findings and show that the migration mechanism and site preference of oxygen vacancies with respect to the Sm dopants is well reproduced. (C) 2016 Elsevier B.V. All rights reserved.

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  • 18.
    Knoop, Florian
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Shulumba, Nina
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Castellano, Aloïs
    Université de Liège, Belgium.
    Alvarinhas Batista, J.P.
    Université de Liège, Belgium.
    Farris, Roberta
    Catalan Institute of Nanoscience and Nanotechnology - ICN2 (BIST and CSIC), Spain.
    Verstraete, Matthieu J.
    Université de Liège, Belgium; University of Utrecht, the Netherlands.
    Heine, Matthew
    Department of Physics, Boston College, USA.
    Broido, David
    Department of Physics, Boston College, USA.
    Kim, Dennis S.
    University of California, USA.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Imperial College London, UK.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergei I.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala University, Sweden.
    Hellman, Olle
    Weizmann Institute of Science, Israel.
    TDEP:Temperature Dependent Effective Potentials2024In: Journal of Open Source Software, E-ISSN 2475-9066, Vol. 9, no 94, article id 6150Article in journal (Refereed)
    Abstract [en]

    The Temperature Dependent Effective Potential (TDEP) method is a versatile and efficient approach to include temperature in a binitio materials simulations based on phonon theory. TDEP can be used to describe thermodynamic properties in classical and quantum ensembles, and several response properties ranging from thermal transport to Neutron and Raman spectroscopy. A stable and fast reference implementation is given in the software package of the same name described here. The underlying theoretical framework and foundation is briefly sketched with an emphasis on discerning the conceptual difference between bare and effective phonon theory, in both self-consistent and non-self-consistent formulations. References to numerous applications and more in-depth discussions of the theory are given.

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  • 19.
    Krenzer, Gabriel
    et al.
    Imperial Coll London, England.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Imperial Coll London, England.
    Tolborg, Kasper
    Imperial Coll London, England; Imperial Coll London, England.
    Rossignol, Hugo
    Trinity Coll Dublin, Ireland; Trinity Coll Dublin, Ireland.
    McCluskey, Andrew R.
    European Spallat Source ER, Denmark.
    Morgan, Benjamin J.
    Univ Bath, England.
    Walsh, Aron
    Imperial Coll London, England; Ewha Womans Univ, South Korea.
    Nature of the Superionic Phase Transition of Lithium Nitride from Machine Learning Force Fields2023In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 35, no 15, p. 6133-6140Article in journal (Refereed)
    Abstract [en]

    Superionic conductors have great potential as solid-stateelectrolytes,but the physics of type-II superionic transitions remains elusive.In this study, we employed molecular dynamics simulations, using machinelearning force fields, to investigate the type-II superionic phasetransition in & alpha;-Li3N. We characterized Li3N above and below the superionic phase transition by calculatingthe heat capacity, Li+ ion self-diffusion coefficient,and Li defect concentrations as functions of temperature. Our findingsindicate that both the Li+ self-diffusion coefficient andLi vacancy concentration follow distinct Arrhenius relationships inthe normal and superionic regimes. The activation energies for self-diffusionand Li vacancy formation decrease by a similar proportion across thesuperionic phase transition. This result suggests that the superionictransition may be driven by a decrease in defect formation energeticsrather than changes in Li transport mechanism. This insight may haveimplications for other type-II superionic materials.

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  • 20.
    Liang, Xia
    et al.
    Imperial Coll London, England.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Imperial Coll London, England.
    Baldwin, William J.
    Univ Cambridge, England.
    Li, Zhenzhu
    Imperial Coll London, England.
    Csanyi, Gabor
    Univ Cambridge, England.
    Walsh, Aron
    Imperial Coll London, England; Ewha Womans Univ, South Korea.
    Structural Dynamics Descriptors for Metal Halide Perovskites2023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 38, p. 19141-19151Article in journal (Refereed)
    Abstract [en]

    Metal halide perovskites have shown extraordinary performance in solar energy conversion technologies. They have been classified as "soft semiconductors" due to their flexible corner-sharing octahedral networks and polymorphous nature. Understanding the local and average structures continues to be challenging for both modeling and experiments. Here, we report the quantitative analysis of structural dynamics in time and space from molecular dynamics simulations of perovskite crystals. The compact descriptors provided cover a wide variety of structural properties, including octahedral tilting and distortion, local lattice parameters, molecular orientations, as well as their spatial correlation. To validate our methods, we have trained a machine learning force field (MLFF) for methylammonium lead bromide (CH3NH3PbBr3) using an on-the-fly training approach with Gaussian process regression. The known stable phases are reproduced, and we find an additional symmetry-breaking effect in the cubic and tetragonal phases close to the phase-transition temperature. To test the implementation for large trajectories, we also apply it to 69,120 atom simulations for CsPbI3 based on an MLFF developed using the atomic cluster expansion formalism. The structural dynamics descriptors and Python toolkit are general to perovskites and readily transferable to more complex compositions.

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  • 21.
    Mopoung, Kunpot
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Ning, Weihua
    Soochow Univ, Peoples R China.
    Zhang, Muyi
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Ji, Fuxiang
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Mukhuti, Kingshuk
    Radboud Univ Nijmegen, Netherlands.
    Engelkamp, Hans
    Radboud Univ Nijmegen, Netherlands.
    Christianen, Peter C. M.
    Radboud Univ Nijmegen, Netherlands.
    Singh, Utkarsh
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Puttisong, Yuttapoom
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Understanding Antiferromagnetic Coupling in Lead-Free Halide Double Perovskite Semiconductors2024In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 128, no 12, p. 5313-5320Article in journal (Refereed)
    Abstract [en]

    Solution-processable semiconductors with antiferromagnetic (AFM) order are attractive for future spintronics and information storage technology. Halide perovskites containing magnetic ions have emerged as multifunctional materials, demonstrating a cross-link between structural, optical, electrical, and magnetic properties. However, stable optoelectronic halide perovskites that are antiferromagnetic remain sparse, and the critical design rules to optimize magnetic coupling still must be developed. Here, we combine the complementary magnetometry and electron-spin-resonance experiments, together with first-principles calculations to study the antiferromagnetic coupling in stable Cs-2(Ag:Na)FeCl6 bulk semiconductor alloys grown by the hydrothermal method. We show the importance of nonmagnetic monovalence ions at the B-I site (Na/Ag) in facilitating the superexchange interaction via orbital hybridization, offering the tunability of the Curie-Weiss parameters between -27 and -210 K, with a potential to promote magnetic frustration via alloying the nonmagnetic B-I site (Ag:Na ratio). Combining our experimental evidence with first-principles calculations, we draw a cohesive picture of the material design for B-site-ordered antiferromagnetic halide double perovskites.

  • 22.
    Mosquera-Lois, Irea
    et al.
    Imperial Coll London, England.
    Kavanagh, Sean R.
    Imperial Coll London, England; UCL, England.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Imperial Coll London, England.
    Tolborg, Kasper
    Imperial Coll London, England.
    Walsh, Aron
    Imperial Coll London, England; Ewha Womans Univ, South Korea.
    Imperfections are not 0 K: free energy of point defects in crystals2023In: Chemical Society Reviews, ISSN 0306-0012, E-ISSN 1460-4744, Vol. 52, no 17, p. 5812-5826Article, review/survey (Refereed)
    Abstract [en]

    Defects determine many important properties and applications of materials, ranging from doping in semiconductors, to conductivity in mixed ionic-electronic conductors used in batteries, to active sites in catalysts. The theoretical description of defect formation in crystals has evolved substantially over the past century. Advances in supercomputing hardware, and the integration of new computational techniques such as machine learning, provide an opportunity to model longer length and time-scales than previously possible. In this Tutorial Review, we cover the description of free energies for defect formation at finite temperatures, including configurational (structural, electronic, spin) and vibrational terms. We discuss challenges in accounting for metastable defect configurations, progress such as machine learning force fields and thermodynamic integration to directly access entropic contributions, and bottlenecks in going beyond the dilute limit of defect formation. Such developments are necessary to support a new era of accurate defect predictions in computational materials chemistry.

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  • 23.
    Nilsson, Johan O.
    et al.
    KTH Royal Institute Technology, Sweden.
    Yu Vekilova, Olga
    KTH Royal Institute Technology, Sweden.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Skorodumova, Natalia V.
    KTH Royal Institute Technology, Sweden; Uppsala University, Sweden.
    Ionic conductivity in Gd-doped CeO2: Ab initio color-diffusion nonequilibrium molecular dynamics study2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 2, p. 024102-Article in journal (Refereed)
    Abstract [en]

    A first-principles nonequilibrium molecular dynamics (NEMD) study employing the color-diffusion algorithm has been conducted to obtain the bulk ionic conductivity and the diffusion constant of gadolinium-doped cerium oxide (GDC) in the 850-1150 K temperature range. Being a slow process, ionic diffusion in solids usually requires simulation times that are prohibitively long for ab initio equilibrium molecular dynamics. The use of the color-diffusion algorithm allowed us to substantially speed up the oxygen-ion diffusion. The key parameters of the method, such as field direction and strength as well as color-charge distribution, have been investigated and their optimized values for the considered system have been determined. The calculated ionic conductivity and diffusion constants are in good agreement with available experimental data.

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  • 24.
    Ning, Weihua
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Tech Univ, Peoples R China.
    Zhao, Xin-Gang
    Jilin Univ, Peoples R China.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bai, Sai
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ji, Fuxiang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    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
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Thermochromic Lead-Free Halide Double Perovskites2019In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 10, article id 1807375Article in journal (Refereed)
    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.

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  • 25.
    Sangiovanni, Davide
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Smirnova, D.
    Ruhr Univ Bochum, Germany; Russian Acad Sci, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gambino, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Mrovec, M.
    Ruhr Univ Bochum, Germany.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Superioniclike Diffusion in an Elemental Crystal: bcc Titanium2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 10, article id 105501Article in journal (Refereed)
    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.

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  • 26.
    Singh, Utkarsh
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala Univ, Sweden.
    Exploring magnetism of lead-free halide double perovskites: A high-throughput first-principles study2023In: Physical Review Materials, E-ISSN 2475-9953, Vol. 7, no 11, article id 114404Article in journal (Refereed)
    Abstract [en]

    We have performed a comprehensive, first-principles high-throughput study of the magnetic properties of halide double perovskites, Cs2BBCl-6, with magnetic ions occupying one or both B and B sites. Our findings indicate a general tendency for these materials to exhibit antiferromagnetic ordering with low Neel temperatures. At the same time, we reveal a few potential candidates that predicted to be ferromagnetic with relatively high Curie temperatures. Achieving ferromagnetic coupling might be feasible via simultaneously alloying at B and B sites with magnetic 3d and nonmagnetic 5d ions. With this approach, we discover that Cs2HgCrCl6, Cs2AgNiCl6, and Cs2AuNiCl6 have high Curie temperatures relative to their peers, with the latter two exhibiting half metallic behavior. Further, this study illuminates the underpinning mechanism of magnetic exchange interactions in halide double perovskites, enabling a deeper understanding of their magnetic behavior. Our findings, especially the discovery of the compounds with robust half metallic properties and high Curie temperatures, hold promise for potential applications in the field of spintronics.

  • 27.
    Spektor, Kristina
    et al.
    ESRF, France.
    Crichton, Wilson A.
    ESRF, France.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Stockholm Univ, Sweden.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Fischer, Andreas
    Augsburg Univ, Germany.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Na-Ni-H Phase Formation at High Pressures and High Temperatures: Hydrido Complexes [NiH5](3-) Versus the Perovskite NaNiH32020In: ACS Omega, E-ISSN 2470-1343, Vol. 5, no 15, p. 8730-8743Article in journal (Refereed)
    Abstract [en]

    The Na-Ni-H system was investigated by in situ synchrotron diffraction studies of reaction mixtures NaH-Ni-H-2 at around 5, 10, and 12 GPa. The existence of ternary hydrogen-rich hydrides with compositions Na3NiH5 and NaNiH3, where Ni attains the oxidation state II, is demonstrated. Upon heating at similar to 5 GPa, face-centered cubic (fcc) Na3NiH5 forms above 430 degrees C. Upon cooling, it undergoes a rapid and reversible phase transition at 330 degrees C to an orthorhombic (Cmcm) form. Upon pressure release, Na3NiH5 further transforms into its recoverable Pnma form whose structure was elucidated from synchrotron powder diffraction data, aided by first-principles density functional theory (DFT) calculations. Na3NiH5 features previously unknown square pyramidal 18- electron complexes NiH53-. In the high temperature fcc form, metal atoms are arranged as in the Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes are dynamically disordered. The Heusler-type metal partial structure is essentially maintained in the low temperature Cmcm form, in which NiH53- complexes are ordered. It is considerably rearranged in the low pressure Pnma form. Experiments at 10 GPa showed an initial formation of fcc Na3NiH5 followed by the addition of the perovskite hydride NaNiH3, in which Ni(II) attains an octahedral environment by H atoms. NaNiH3 is recoverable at ambient pressures and represents the sole product of 12 GPa experiments. DFT calculations show that the decomposition of Na3NiH5 = NaNiH3 + 2 NaH is enthalpically favored at all pressures, suggesting that Na3NiH5 is metastable and its formation is kinetically favored. Ni-H bonding in metallic NaNiH3 is considered covalent, as in electron precise Na3NiH5, but delocalized in the polyanion [NiH3](-).

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  • 28.
    Spektor, Kristina
    et al.
    ESRF, France.
    Crichton, Wilson A.
    ESRF, France.
    Konar, Sumit
    Univ Edinburgh, Scotland; Univ Edinburgh, Scotland.
    Filippov, Stanislav
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Unraveling Hidden Mg-Mn-H Phase Relations at High Pressures and Temperatures by in Situ Synchrotron Diffraction2018In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 57, no 3, p. 1614-1622Article in journal (Refereed)
    Abstract [en]

    The MgMnH system was investigated by in situ high pressure studies of reaction mixtures MgH2MnH2. The formation conditions of two complex hydrides with composition Mg3MnH7 were established. Previously known hexagonal Mg3MnH7 (h-Mg3MnH7) formed at pressures 1.52 GPa and temperatures between 480 and 500 degrees C, whereas an orthorhombic form (o-Mg3MnH7) was obtained at pressures above 5 GPa and temperatures above 600 degrees C. The crystal structures of the polymorphs feature octahedral [Mn(I)H-6](5) complexes and interstitial H-. Interstitial H- is located in trigonal bipyramidal and square pyramidal interstices formed by Mg2+ ions in h- and o-Mg3MnH7, respectively. The hexagonal form can be retained at ambient pressure, whereas the orthorhombic form upon decompression undergoes a distortion to monoclinic Mg3MnH7 (m-Mg3MnH7). The structure elucidation of o- and m-Mg3MnH7 was aided by first-principles density functional theory (DFT) calculations. Calculated enthalpy versus pressure relations predict m- and o-Mg3MnH7 to be more stable than h-Mg3MnH7 above 4.3 GPa. Phonon calculations revealed o-Mg3MnH7 to be dynamically unstable at pressures below 5 GPa, which explains its phase transition to m-Mg3MnH7 on decompression. The electronic structure of the quenchable polymorphs h- and m-Mg3MnH7 is very similar. The stable 18-electron complex [MnH6](5-) is mirrored in the occupied states, and calculated band gaps are around 1.5 eV. The study underlines the significance of in situ investigations for mapping reaction conditions and understanding phase relations for hydrogen-rich complex transition metal hydrides.

  • 29.
    Yuan, Fanglong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Beijing Normal Univ, Peoples R China.
    Folpini, Giulia
    Ist Italiano Tecnol, Italy.
    Liu, Tianjun
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Singh, Utkarsh
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Treglia, Antonella
    Ist Italiano Tecnol, Italy; Politecn Milan, Italy.
    Lim, Jia Wei Melvin
    Nanyang Technol Univ, Singapore.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergei I.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Sum, Tze Chien
    Nanyang Technol Univ, Singapore.
    Petrozza, Annamaria
    Ist Italiano Tecnol, Italy.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Bright and stable near-infrared lead-free perovskite light-emitting diodes2024In: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893Article in journal (Refereed)
    Abstract [en]

    Long-wavelength near-infrared light-emitting diodes (NIR LEDs) with peak emission wavelengths beyond 900 nm are of critical importance for various applications including night vision, biomedical imaging, sensing and optical communications. However, the low radiance and poor operational stability of state-of-the-art long-wavelength NIR LEDs based on soft materials remain the most critical factors limiting their practical applications. Here we develop NIR LEDs emitting beyond 900 nm with improved performance through the rational manipulation of p doping in all-inorganic tin perovskites (CsSnI3) by retarding and controlling the crystallization process of perovskite precursors in tin-rich conditions. The resulting NIR LEDs exhibit a peak emission wavelength at 948 nm, high radiance of 226 W sr-1 m-2 and long operational half-lifetime of 39.5 h at a high constant current density of 100 mA cm-2. Our demonstration of efficient and stable NIR LEDs operating at high current densities may also open up new opportunities towards electrically pumped lasers. Controlling the intrinsic doping of lead-free perovskites enables near-infrared LEDs emitting at 948 nm with a peak radiance of 226 W sr-1 m-2 and a half-lifetime of 39.5 h.

  • 30.
    Zhang, Bin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ji, Fuxiang
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering. Uppsala Univ, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Rudko, Galyna
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Chen, Weimin
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Buyanova, Irina
    Linköping University, Department of Physics, Chemistry and Biology, Electronic and photonic materials. Linköping University, Faculty of Science & Engineering.
    Lattice Dynamics and Electron-Phonon Coupling in Double Perovskite Cs2NaFeCl62023In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 127, no 4, p. 1908-1916Article in journal (Refereed)
    Abstract [en]

    Phonon-phonon and electron/exciton-phonon coupling play a vitally important role in thermal, electronic, as well as optical properties of metal halide perovskites. In this work, we evaluate phonon anharmonicity and coupling between electronic and vibrational excitations in novel double perovskite Cs2NaFeCl6 single crystals. By employing comprehensive Raman measurements combined with first-principles theoretical calculations, we identify four Raman-active vibrational modes. Polarization properties of these modes imply Fm (3) over barm symmetry of the lattice, indicative for on average an ordered distribution of Fe and Na atoms in the lattice. We further show that temperature dependence of the Raman modes, such as changes in the phonon line width and their energies, suggests high phonon anharmonicity, typical for double perovskite materials. Resonant multiphonon Raman scattering reveals the presence of high-lying band states that mediate strong electron-phonon coupling and give rise to intense nA(1g) overtones up to the fifth order. Strong electron-phonon coupling in Cs2NaFeCl6 is also concluded based on the Urbach tail analysis of the absorption coefficient and the calculated Frohlich coupling constant. Our results, therefore, suggest significant impacts of phonon-phonon and electron-phonon interactions on electronic properties of Cs2NaFeCl6, important for potential applications of this novel material.

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