First principle study on stability of monoclinic and

orthorhombic indium oxide

Arthi D¹, Vasu Veerapandy¹ and Ponniah Vajeeston² 

¹School of Physics, Madurai Kamaraj University, Madurai, India. 

²Center for Materials Science and Nanotechnology, University of Oslo, Norway.

Abstract:

Over the past years, metal oxide semiconductors (MOSs) have drawn tremendous attention to materials scientists due to their widespread applications. Amongst various MOSs, indium oxide (In₂O₃) has been investigated extensively owing to its wide band gap, stability, high electrical conductivity and excellent optoelectronic properties. The crystalline form exists in two phases, the cubic (bixbyite type) and rhombohedral (corundum type). Although pure In₂O₃ is hardly used in technological applications, it is the forerunner of many transparent conducting oxides (TCO) and transparent oxide semiconductor (TOS) systems. The main objective of this study is to explore the other possible stable phases of In₂O₃. The structural, electronic, mechanical, vibrational and thermal properties of 6 low-energy bulk In₂O₃ polytypes are studied using density functional theory. A detailed description of the structural properties and studies on stability is presented. We have performed the calculations using the Vienna ab initio Simulation Package (VASP) based on DFT. Calculated the lattice and positional parameters have been established from structural optimization based on total energy calculations, which are in good match with the available experimental data. The electronic properties were computed by HSE-06 for the polytypes. In₂O₃ has semi-metallic properties, according to electronic band structure investigations. Evaluated the mechanical stability by computing the single-crystal elastic constants and then by linear fitting of the stress-strain curve. The elastic constants reveal the compound's hardness. Calculated Poisson’s and Pugh’s ratio confirms that all stable polytypes are ductile. The VASP code is used for calculating the real space force constants of supercells, and the PHONOPY code is used for calculating the phonon frequencies. The thermal properties including heat capacity and entropy were obtained. Observed that all polytypes have very high thermal capacity. This study reports on a general understanding of the Raman and IR activities of the phonon modes.