Phase stability, electronic structure, and optical properties of indium oxide polytypes

TLDR

The authors used first‑principles density‑functional calculations to study phase stability, electronic structure, optical properties, high‑pressure behavior, and carrier effective masses of In₂O₃ polytypes in the I2₁3, Ia¯3, and R¯3 space groups. Structural optimization reproduces experimental lattice parameters, with the I2₁3 phase converging to Ia¯3; Ia¯3 undergoes a pressure‑induced transition to R¯3 near 3.8 GPa; band‑structure analysis shows I2₁3 and R¯3 are indirect band‑gap semiconductors while Ia¯3 is direct‑gap; charge‑density analysis reveals predominantly ionic bonding with some covalent In–O interaction, and Ia¯3 and R¯3 exhibit low absorption and reflection below 5 eV, indicating transparency.

Abstract

Structural phase stability, electronic structure, optical properties, and high-pressure behavior of polytypes of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ in three space group symmetries $I{2}_{1}3$, $Ia\overline{3}$, and $R\overline{3}$ are studied by first-principles density-functional calculations. From structural optimization based on total energy calculations, lattice and positional parameters have been established, which are found to be in good agreement with the corresponding experimental data except for $I{2}_{1}3$, where the symmetry analysis for optimized structure indicates that it arrived at the $Ia\overline{3}$ phase. ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ of space group symmetry $Ia\overline{3}$ is found to undergo a pressure-induced phase transition to the $R\overline{3}$ phase at pressures around $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. From the analysis of band structure coming out from the calculations within the local density and generalized gradient approximations, it is found that ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ of space group symmetry $I{2}_{1}3$ and $R\overline{3}$ are indirect band gap semiconductors, while the other phase of space group $Ia\overline{3}$ is having direct band gap. The calculated carrier effective masses for all these three phases are compared with available experimental and theoretical values. From charge-density and electron localization function analysis, it is found that these phases have dominant ionic bonding with noticeable covalent interaction between indium and oxygen. The magnitudes of the absorption and reflection coefficients for ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ with space groups $Ia\overline{3}$ and $R\overline{3}$ are small in the energy range $0--5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, indicating that these phases can be regarded and classified as transparent.