First-principles calculations of group IIA and group IV impurities in α−Al2O3

Abstract

$\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ is widely used for high-temperature structural materials in the form of polycrystals, and the physical and chemical properties are significantly influenced by the impurity types and their concentrations. Although the concentrations of some impurities in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ have been experimentally investigated, there are no detailed reports on the point-defect structures and their charge states. In this study, we systematically investigate the point-defect structures of native defects, group IIA (Be, Mg, Ca, Sr, and Ba) and group IV (C, Si, Ge, Sn, and Pb) impurities by using Heyd-Scuseria-Ernzerhof hybrid functional combined with a finite-size supercell correction. We found that although the favorable defect types in the group IIA impurities are independent of the atmosphere (or oxygen partial pressure), the impurity defects in group IV show a strong dependence on the atmosphere and the impurity types. On the basis of the defect energetics, we calculate the impurity concentrations as a function of temperature for the respective extreme conditions. This could be useful for controlling the properties of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$, especially sintering behaviors.