Kazuaki Toyoura

First-principles calculations on slip system activation in the rock salt structure: electronic origin of ductility in silver chloride

Abstract First principles calculations were performed to understand an electronic origin of high ductility in silver chloride (AgCl) with the rock salt structure. From calculations of generalised stacking fault energies for different slip systems, it was found that only the {1u20091u20090} slip system is favourably activated in sodium chloride (NaCl) with the same rock salt structure, whereas AgCl shows three kinds of possible slip systems along the direction on the {0u20090u20091}, {1u20091u20090}, and {1u20091u20091} planes, which is in excellent agreement with experiment. Detailed analyses of the electronic structures across slip planes showed that the more covalent character of bonding of Ag–Cl than Na–Cl tends to make the slip motion energetically favourable. It was also surprising to find out that strong Ag–Ag covalent bonds across the slip plane are formed in the {0u20090u20091}〈1u20091u20090〉 slip system in AgCl, which makes it possible to activate the multiple slip systems in AgCl.

First-principles study of defect equilibria in lithium zinc nitride

First-principles calculations are performed in order to investigate defect equilibria in lithium zinc nitride (LiZnN). The formation energies of native defects and their thermal equilibrium concentrations are evaluated, considering vacancies, interstitials, and cation anti-site defects under relevant conditions of chemical potentials. It is clarified that acceptor-like Li anti-sites are dominant under ordinary pN2–T conditions. The concentrations of donor-like defects, which can compensate the negative charge of ionized Li anti-sites, are much lower. This results in the formation of holes with a high concentration even in undoped LiZnN.

Structural and Optical Properties of LiZnN Prepared by Electrochemical Formation in a LiCl–KCl–Li3N Melt

The structural and optical properties of LiZnN prepared by potentiostatic electrolysis of a Zn electrode at 0.7 V (Li + /Li) in LiCl-KCl-Li 3 N were investigated. An X-ray diffraction analysis clarified that the obtained film consisted of a single-phase LiZnN (lattice constant 0.490 nm, crystallite size 60 nm, film thickness 5 μm for 2 h). Reflectance measurements revealed that LiZnN has a direct bandgap of 1.9 eV at room temperature. Furthermore, a red luminescence has been confirmed by irradiation of 325-nm and 442-nm light at 6-150 K. This luminescence is interpreted to result from electron-hole recombination between conduction and valence bands or shallow levels of defects or impurities, as the luminescence band contains three sub-bands, and all of them correspond to or close to the estimated bandgap energy.

Potential Energy Surface Mapping of Charge Carriers in Ionic Conductors Based on a Gaussian Process Model

The potential energy surface (PES) of a charge carrier in a host crystal is an important concept to fundamentally understand ionic conduction. Such PES evaluations, especially by density functional theory (DFT) calculations, generally require vast computational costs. This chapter introduces a novel selective sampling procedure to preferentially evaluate the partial PES characterizing ionic conduction. This procedure is based on a machine learning method called the Gaussian process (GP), which reduces computational costs for PES evaluations. During the sampling procedure, a statistical model of the PES is constructed and sequentially updated to identify the region of interest characterizing ionic conduction in configuration space. Its efficacy is demonstrated using a model case of proton conduction in a well-known proton-conducting oxide, barium zirconate (BaZrO3) with the cubic perovskite structure. The proposed procedure efficiently evaluates the partial PES in the region of interest that characterizes proton conduction in the host crystal lattice of BaZrO3.

Dislocation at a {2\( \bar{1} \) \( \bar{1} \)0} low-angle grain boundary in LiNbO3

A LiNbO3 bicrystal that contains a {21¯documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}

Optical properties of zinc nitride formed by molten salt electrochemical process

bar{1}

Structural and optical properties of magnesium nitride formed by a novel electrochemical process

end{document}1¯documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}