Band Structure Calculations of the High‐Temperature Electronic Structure of Magnesium Oxide

Abstract

The effects of high temperature on the electronic structure of a material consist of two major contributions, thermal lattice expansion and the electron‐phonon interaction. These can produce dramatic changes in the electronic structure and play a critical role in the high‐temperature properties and behavior of ceramics. We have used ab initio pseudofunction band structure methods to calculate the temperature dependence of the electronic structure of MgO from 300 to 1300 K modeling the independent effects of thermal lattice expansion and the electron‐phonon interaction. The band structure calculations were performed self‐consistently on a (MgO)4 supercell using experimental values obtained from high‐temperature X‐ray diffraction to determine the lattice constants up to 1300 K and the root mean square amplitude of phonon displacements. Lattice thermal expansion contributed ‐0.15 meV/K to the band gap temperature dependence. Individual phonon modes, with displacements in the 〈111〉, 〈110〉, and 〈100〉 directions, were modeled using distorted lattice calculations. The electron‐phonon coupling was found to be strongest for the 〈100〉 mode modeled, with strong coupling seen for modes which lead to the smallest decrease in the Mg‐O bond length. The overall magnitude of the electron‐phonon contribution to the band gap temperature dependence for the phonon modes modeled was −0.95 meV/K. The theoretical results account for a band gap temperature dependence in MgO of −1.1 meV/K, which compares well with the temperature dependence of approximately −1 meV/K determined experimentally using vacuum ultraviolet spectroscopy.