First-Principles Calculations of Point Defect Formation and Anion Diffusion Mechanisms in the Oxyhydride Ba2ScHO3

10.26434/chemrxiv.12121254.v2 ◽

2020 ◽

Author(s):

Akihide Kuwabara ◽

Fumitake Takeiri ◽

Haq Nawaz ◽

Genki Kobayashi

Keyword(s):

Point Defect ◽

First Principles ◽

Defect Formation ◽

Diffusion Mechanism ◽

Layered Perovskite ◽

First Principles Calculations ◽

Ion Conductor ◽

Hydride Ion ◽

Anion Diffusion ◽

Hydride Ions

<div>Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing hydrogen. La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub> oxyhydride with a layered perovskite (K<sub>2</sub>NiF<sub>4</sub>-type) structure was discovered as a hydride ion conductor, and it was subsequently reported that Ba<sub>2</sub>ScHO<sub>3</sub> with the same crystal structure is also a hydride ion conductor. The two compounds have different anionic sites occupied by hydride ions. In La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub>, the hydride ions occupy equatorial anion sites, while the hydride ions are located at apical anion sites in Ba<sub>2</sub>ScHO<sub>3</sub>. This suggests that hydride ions diffuse through rock-salt layers in Ba<sub>2</sub>ScHO<sub>3</sub>. However, the specific diffusion mechanism resulting in ionic conductivity of Ba<sub>2</sub>ScHO<sub>3</sub> has not been clarified yet. In the present study, the point defect</div><div>formation energies and anionic conduction mechanisms of Ba<sub>2</sub>ScHO<sub>3</sub> were systematically analyzed using first-principles calculations. As a result, hydride ionic defects tend to form preferentially in Ba<sub>2</sub>ScHO<sub>3</sub> rather than oxide ions. The migration energies of vacancy, interstitial and interstitialcy mechanisms were evaluated, and the activation energies of hydride ionic diffusion mediated by the vacancy and the interstitialcy processes was found to be the lowest.</div>

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First-Principles Calculations of Point Defect Formation and Anion Diffusion Mechanism in Oxyhydride Ba2ScHO3

10.26434/chemrxiv.12121254.v1 ◽

2020 ◽

Author(s):

Akihide Kuwabara ◽

Fumitake Takeiri ◽

Haq Nawaz ◽

Genki Kobayashi

Keyword(s):

Point Defect ◽

First Principles ◽

Defect Formation ◽

Diffusion Mechanism ◽

Layered Perovskite ◽

First Principles Calculations ◽

Ion Conductor ◽

Hydride Ion ◽

Anion Diffusion ◽

Hydride Ions

<div>Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing </div><div>hydrogen. La2-x-ySrx+yLiH1-x+yO3-y oxyhydride with a layered perovskite (K2NiF4-type) structure was </div><div>discovered as a hydride ion conductor, and it was subsequently reported that Ba2ScHO3 with the same </div><div>crystal structure is also a hydride ion conductor. The two compounds have different anionic sites </div><div>occupied by hydride ions. In La2-x-ySrx+yLiH1-x+yO3-y, the hydride ions occupy equatorial anion sites, </div><div>while the hydride ions are located at apical anion sites in Ba2ScHO3. This suggests that hydride ions </div><div>diffuse through rock-salt layers in Ba2ScHO3. However, the specific diffusion mechanism resulting in </div><div>ionic conductivity of Ba2ScHO3 has not been clarified yet. In the present study, the point defect </div><div>formation energies and anionic conduction mechanisms of Ba2ScHO3 were systematically analyzed </div><div>using first-principles calculations. As a result, hydride ionic defects tend to form preferentially in </div><div>Ba2ScHO3 rather than oxide ions. The migration energies of vacancy, interstitial and interstitialcy </div><div>mechanisms were evaluated, and the activation energies of hydride ionic diffusion mediated by the </div><div>vacancy and the interstitialcy processes was found to be the lowest.</div>

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First Principles Calculations of Defects in Unstable Crystals: Austenitic Iron

MRS Proceedings ◽

10.1557/opl.2011.1383 ◽

2011 ◽

Vol 1363 ◽

Cited By ~ 1

Author(s):

G.J. Ackland ◽

T.P.C. Klaver ◽

D.J. Hepburn

Keyword(s):

Point Defects ◽

First Principles ◽

Defect Formation ◽

Single Layer ◽

Temperature Limit ◽

Reference State ◽

First Principles Calculations ◽

General Picture ◽

Bcc Iron ◽

Defect Energies

ABSTRACTFirst principles calculations have given a new insight into the energies of point defects in many different materials, information which cannot be readily obtained from experiment. Most such calculations are done at zero Kelvin, with the assumption that finite temperature effects on defect energies and barriers are small. In some materials, however, the stable crystal structure of interest is mechanically unstable at 0K. In such cases, alternate approaches are needed. Here we present results of first principles calculations of austenitic iron using the VASP code. We determine an appropriate reference state for collinear magnetism to be the antiferromagnetic (001) double-layer (AFM-d) which is both stable and lower in energy than other possible models for the low temperature limit of paramagnetic fcc iron. Another plausible reference state is the antiferromagnetic (001) single layer (AFM-1). We then consider the energetics of dissolving typical alloying impurities (Ni, Cr) in the materials, and their interaction with point defects typical of the irradiated environment. We show that the calculated defect formation energies have fairly high dependence on the reference state chosen: in some cases this is due to instability of the reference state, a problem which does not seem to apply to AFM-d and AFM-1. Furthermore, there is a correlation between local free volume magnetism and energetics. Despite this, a general picture emerge that point defects in austenitic iron have geometries similar to those in simpler, non-magnetic, thermodynamically stable FCC metals. The defect energies are similar to those in BCC iron. The effect of substitutional Ni and Cr on defect properties is weak, rarely more than tenths of eV, so it is unlikely that small amounts of Ni and Cr will have a significant effect on the radiation damage in austenitic iron at high temperatures.

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On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy

EPJ Photovoltaics ◽

10.1051/epjpv/2017006 ◽

2017 ◽

Vol 8 ◽

pp. 85505 ◽

Cited By ~ 2

Author(s):

Pia Seeberger ◽

Julien Vidal

Keyword(s):

Point Defect ◽

First Principles ◽

Defect Formation ◽

Finite Size ◽

Direct Calculation ◽

Finite Size Effects ◽

Numerical Errors ◽

Silicon Vacancy ◽

Size Dependent ◽

Very High

Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and –2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.

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New Pt-based Superalloy System Designed from First Principles

MRS Proceedings ◽

10.1557/proc-1128-u05-28 ◽

2008 ◽

Vol 1128 ◽

Author(s):

Vsevolod I. Razumovskiy ◽

Eyvaz I. Isaev ◽

Andrei V. Ruban ◽

Pavel A. Korzhavyi

Keyword(s):

Elastic Properties ◽

First Principles ◽

Defect Formation ◽

Alloy System ◽

First Principles Calculations ◽

Phonon Spectra ◽

Ultrahigh Temperature ◽

New Generation ◽

Formation Energies ◽

Temperature Applications

AbstractPt-Sc alloys with the γ-γ′ microstructure are proposed as a basis for a new generation of Pt-based superalloys for ultrahigh-temperature applications. This alloy system was identified on the basis of first-principles calculations. Here we discuss the prospects of the Pt-Sc alloy system on the basis of calculated elastic properties, phonon spectra, and defect formation energies.

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Bulk properties and transport mechanisms of a solid state antiperovskite Li-ion conductor Li3OCl: insights from first principles calculations

Journal of Materials Chemistry A ◽

10.1039/c7ta08780b ◽

2018 ◽

Vol 6 (3) ◽

pp. 1150-1160 ◽

Cited By ~ 19

Author(s):

Musheng Wu ◽

Bo Xu ◽

Xueling Lei ◽

Kelvin Huang ◽

Chuying Ouyang

Keyword(s):

Solid State ◽

Systematic Study ◽

First Principles ◽

First Principles Calculations ◽

Transport Mechanisms ◽

Bulk Properties ◽

Ion Conductor ◽

Fast Ion Conductor ◽

Li Ion ◽

Fast Ion

Systematic study on bulk properties, defect chemistry and Li-ion transport mechanisms of a Li3OCl fast-ion conductor.

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Theory of Hydrogen Interactions with Amorphous Silicon

MRS Proceedings ◽

10.1557/proc-557-275 ◽

1999 ◽

Vol 557 ◽

Cited By ~ 8

Author(s):

Chris G. Van De Walle ◽

Blair Tuttle

Keyword(s):

Amorphous Silicon ◽

First Principles ◽

Molecular Hydrogen ◽

Hydrogen Exchange ◽

Defect Formation ◽

Exchange Process ◽

Current Understanding ◽

First Principles Calculations ◽

Microscopic Mechanism ◽

Enhanced Stability

AbstractWe present an overview of recent results for hydrogen interactions with amorphous silicon (a-Si), based on first- principles calculations. We review the current understanding regarding molecular hydrogen, and show that H2 molecules are far less inert than previously assumed. We then discuss results for motion of hydrogen through the material, as relating to diffusion and defect formation. We present a microscopic mechanism for hydrogen-hydrogen exchange, and examine the metastable ≠ SiH2 complex formed during the exchange process. We also discuss the enhanced stability of Si-D compared to Si-H bonds, which may provide a means of suppressing light-induced defect generation.

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