High-temperature emissivity of silica, zirconia and samaria from ab initio simulations: role of defects and disorder

Abstract

Understanding and eventually controlling the high-temperature spectral emissivity of ceramic materials is important for a range of applications, including thermal barrier coatings. In this paper, we use ab initio density functional theory simulations to predict the emissivity of silica, zirconia and rare-earth oxides. High-temperature emissivity is dominated by processes with energies lower than the band gap of these materials and we focus on how dynamic and static features in the atomic structure of these materials (including defects, glasses and thermal fluctuations) enable transitions with desired energies. We find that neutral oxygen vacancies contribute significantly to the high emissivity of ZrO2. On the other hand, neutral point defects in α and amorphous silica fail to provide transitions with energies significantly below the band gap, explaining the low emissivity of this material. In the case of Sm2O3, we find that transitions between localized f-electron states as well as point defects contribute to its high emissivity. Interestingly, dynamical changes in electronic structure in samples taken from molecular dynamics simulations of molten materials lead to a significant increase in their emissivity.