Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J56: Computational Design and Discovery of Novel Materials: Oxides and Related SemiconductorsFocus Live
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Sponsoring Units: DMP DCOMP Chair: Michele Kotiuga, Ecole Polytechnique Federale de Lausanne |
Tuesday, March 16, 2021 3:00PM - 3:36PM Live |
J56.00001: Computational discovery of ultra-wide-band-gap semiconductors Invited Speaker: Emmanouil Kioupakis Our aim is to understand the factors that distinguish ultra-wide-band-gap (UWBG) semiconductors from insulators, and to discover new UWBG semiconducting materials that surpass the current state of the art. Despite decades of research, only a handful of UWBG semiconductors have been developed to date, and they all face challenges due to poor dopability and/or low conductivity. We apply predictive atomistic calculations in order to understand the fundamental limitations of current UWBG semiconductors such as Ga2O3 and AlGaN, and to discover new materials with improved functionality compared to the current state of the art. Our calculations uncovered the rutile polytype of GeO2 as a promising UWBG semiconductor with shallow donors and relatively shallow acceptors, high carrier mobilities, and high thermal conductivity that can overcome the limitations of Ga2O3 in power electronics. Moreover, we have discovered several compounds with gaps wider than AlN (6.2 eV) that host shallow dopants and mobile carriers. Our analysis revealed that there is no upper band-gap limit that separates semiconductors from insulators and uncovers the rules to design new UWBG semiconductors with improved functional properties. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J56.00002: Ab initio thermodynamics of transition metal oxides for thermochemical energy storage. Suzanne Wallace, Ambroise van Roekeghem, Anton Bochkarev, Javier Carrasco, Alexander Shapeev, Natalio Mingo (CoxMn1−x)3O4 is a promising candidate material for solar thermochemical energy storage. Modelling this system is challenging due to the varied sources affecting the free energy, and the prohibitive amount of configurations needed in the configurational entropy calculation. We present an accurate prediction of the experimental hausmannite-spinel SG in the case of (CoxMn1−x)3O4, using machine learning to extend an ab initio dataset of hundreds of structures, and including many different entropic contributions to the free energy. We then compare three different machine learning approaches for sampling the configuration space, and assess the accuracy of model predictions via the experimental phase diagram. Finally, we discuss how species mixing can increase the energy storage capacity of redox reactions with transition metal oxides and decrease their embodied energy cost. In the case of (CoxMn1−x)3O4, a simple calculation suggests possible storage capacities over 30% higher than that of pure Co3O4, in agreement with previous measurements. Theoretical considerations like these may be useful when trying to determine if thermochemical energy storage could replace the current use of molten salts in concentrated solar power generation. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J56.00003: Rational design of bismuth-based oxide double-perovskite semiconductors with large band-gap tunability Arashdeep Thind, Charlie Loitman, ZHAOHAN ZHANG, Steven Hartman, Ghanshyam Pilania, Rohan Mishra Bismuth-based halide double perovskites, such as Cs2AgBiBr6, have emerged as a new class of semiconductors with applications in solar-energy harvesting and optoelectronics. However, these halides suffer from long-term stability issues due to the weak metal-halogen bonds. We have explored Bi-based oxide double perovskites as an alternative class of semiconducting materials. The oxide framework improves stability due to stronger metal-oxygen bonds and the -2 charge of the oxide anion opens a vast cation composition space to tune the electronic structure of the material. We use a combination of high-throughput density-functional-theory calculations and machine learning to screen through the vast composition space of over 29,000 A'A"M'BiO6 hypothetical oxide double perovskites. We predict various stable compounds within the A'A"M'BiO6 composition space, where M' = V, Mo, W, Ta, Nb, Sb,and Te, which can find applications as stand-alone absorbers, absorbers in tandem solar cells and as photocatalysts. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J56.00004: Prospects for High Carrier Mobility in the Cubic Germanates Andrew Rowberg, Karthik Krishnaswamy, Chris Van de Walle Barium stannate (BaSnO3) has attracted considerable interest on account of its wide band gap and record-high room-temperature mobility (320 cm2V-1s-1); however, comparatively little attention has been paid to the cubic germanates (SrGeO3 and BaGeO3). Here, we comprehensively examine the electronic structure properties of both materials using density functional theory calculations with an accurate hybrid functional. We find that the germanates have wide band gaps and low carrier effective masses; the hole effective masses, in particular, are considerable smaller than those of BaSnO3 [1]. We then proceed to consider electron mobility in SrGeO3, the most promising system based on reports of its experimental synthesis. We find SrGeO3 to have a total electron mobility between 400 and 500 cm2V-1s-1, significantly surpassing our previously calculated value for BaSnO3, value and making it worthy of further study. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J56.00005: Prediction of New Ferroelectric Clathrate and Polar Oxynitrides Ronald Cohen, Li Zhu, Hiroyuki Takenaka, Timothy A Strobel We predict using DFT a new ferroelectric clathrate with composition ScB3C3, which exhibits high polarization density and low mass density (PRL 125, 127601, 2020). Molecular dynamics simulations show spontaneous polarization with a Tc of ∼370 K. We have also simulated a variety of oxynitrides as functions of pressure and epitaxial strain (arXiv:2008.06582). We find that the P4mm perovskite structures of YGeO2N, LaSiO2N, and LaGeO2N are dynamically stable at zero pressure, and thus should be synthesizable by pulsed laser deposition or other atomic layer deposition methods. In addition we find that ferroelectric polar phases of perovskite-structured oxynitrides can be thermodynamically stable and synthesized at high pressure on appropriate substrates. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J56.00006: Accelerated search for novel ferroelectric materials Ramon Frey, Aria Mansouri, Bastien Grosso, Nicola A. Spaldin We report the development of a combined machine learning and high-throughput DFT framework to accelerate the search for novel ferroelectrics. This framework is capable of predicting potential ferroelectric compounds using only compositions as input. Initially, for a given chemical composition-space, a series of machine learning algorithms predict the possible stable stoichiometries that are insulating and have a non-centrosymmetric structure, necessary for the ferroelectricity. A final classification model then predicts the point groups of these stoichiometries. Based on the point groups, a subsequent series of high-throughput DFT calculations determine the ground state crystal structure. As a final step, using group theory considerations, non-polar parent structures are identified and the polarisation values are further determined. By predicting the crystal structures as well as the polarisation values, this method provides a powerful tool to explore new ferroelectric materials beyond the existing databases. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J56.00007: A MoON Race: Computational Design of a Heteroanionic Metal-Insulator Transition Compound Molybdenum Oxynitride Lauren Walters, Nathan J Szymanski, Danilo Puggioni, James M Rondinelli Using symmetry principles and electronic structure calculations we designed a novel metal-insulator transition (MIT) compound MoON [1]. The alpha and beta phase of this material were identified from a set of prototype AB2 structures based upon energetics, band gap, and the c/a ratio. We show that the fac ordering of the polyhedra are important for charge localization, singlet formation, and opening of the band gap. Our density functional calculations show how changes in the electronic band gap are driven by structural distortions, including 1D chain canting and dimer formation. Last we draw parallels between MoON and the well-studied VO2, demonstrating that properties such as the c/a lattice parameter ratio could be used for further design and identification of other rutile MIT materials. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J56.00008: Quantifying the stability of the anion ordering in SrVO2H Masayuki Ochi, Kazuhiko Kuroki Transition metal oxides are of particular importance in condensed matter physics due to their wide variety of physical properties. Transition metal cations therein play a major role in determining their physical properties; anions, on the other hand, have been regarded as subsidiary constituents. However, mixed-anion strategy – a control of materials properties through multiple anions – have recently attracted increasing attention. Although employing anion degrees of freedom is a fascinating idea, a crucial problem is that the anion configuration in crystal is hard to control while it can drastically change materials properties. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J56.00009: Conductivity, elastic moduli and phase transitions in the Li10GeP2O12 solid-state electrolyte from first-principles molecular dynamics Giuliana Materzanini, Leonid Kahle, Aris Marcolongo, Nicola Marzari Superionic materials are ideal candidates to replace the conductive but flammable liquid organic electrolytes currently used, leading to prospectively safer all-solid-state batteries. Aiming to find highly conductive candidates that have the appealing electrochemical properties of an oxide, we study here extensively LGPO, the oxide analogue of LGPS, one of the best conducting solid-state electrolytes. We find that for LGPO a hypothetical tetragonal phase mirroring that of LGPS would be highly conductive. We thus employ isobaric-isoenthalpic simulations to explore phase stability and phase transitions, while extracting from the trajectories the relevant elastic moduli. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J56.00010: Insight into the energetics and properties of oxyfluorides through anion ordering Richard Saballos, James M Rondinelli Ordered cation and oxygen vacancies is an established route to tune the properties of transition metal oxide double perovskites. However, less is known about what role these structural vacancies can play in materials comprising two unique anions, for example, transition metal oxyfluorides. Here we use the experimentally known double perovskite [ ]KNaNbOF5 with P4/nmm symmetry to generate all possible unique anion orderings. We generated 346 structures based on combinations of cation and anion vacancies in the presence of octahedral rotations. We found 94% of the structures are non-centrosymmetric, which could possibly support interesting electronic phenomena. Furthermore, a subset of these structures exhibit octahedral tilting without any external stimuli. By analyzing structural features in conjunction with orbital interactions, we explain how control of the anion ordering can lead to changes in the energetics and electronic properties of oxyfluorides. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J56.00011: The linear electro-optical effect in thin oxide films Alexander Demkov, Ali Hamze, Wente Li, Therese Paoletta, Kurt Fredrickson The linear electro-optical (EO) effect, also known as the Pockels effect, has been the subject of increasing interest due to its potential for use in silicon photonic applications. As such, it is necessary to find materials that have a strong EO response in thin film form, which is essential for low power and small footprint devices. In this talk we will discuss general design rules for developing strong Pockels materials inferred from first principles theory. We will discuss the Pockels effect in BaTiO3, strained SrTiO3, LiB3O5 (LBO) and CsB3O5 (CBO) and use these materials as prototypical examples of where conventional wisdom breaks down. We analyze how the EO response is related to the optical phonon frequencies, Raman susceptibility and mode polarization and elucidate the underlying physical phenomena behind the large Pockels effect. |
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