Formation Energy Calculations of Native Defects in Alumina and Silica

Abstract

Al₂O₃ and SiO₂ are important protective oxides formed on the metal surface at high temperatures. Information of defect structures is crucial for understanding properties of these oxides and also for designing new alloys with superior protective oxide film. For these purposes, formation energies of various defects in Al₂O₃ and SiO₂ are calculated by using the plane-wave pseudopotential method. Also, the formation energies of Shottky defects and Frenkel defects are evaluated on the basis of these calculations. It is shown that formation energies of these defects are higher in SiO₂ than in Al₂O₃. In other words, less defects are formed in SiO₂ than in Al₂O₃. It is also found that the principal defect is the cation Frenkel defect in Al₂O₃ but the anion Frenkel defect in SiO₂. These results agree with the experimental results that Al ions diffuse mainly in Al₂O₃ but oxygen ions diffuse in SiO₂.