Electronic structure and point defect concentrations of C11b MoSi2 by first-principles calculations

Abstract

The electronic structure and point defect concentrations of C11b MoSi2 were studied systematically by the first-principles calculations based on density functional theory. Mo vacancy-induced charge density shows strong directional covalent bonds caused by hybridization of Mo-4d and Si-3p orbitals, which indicates that MoSi2 has low fracture toughness at room temperature. Combining with Wagner–Schottky model, these point defect concentrations of C11b MoSi2 at 2173, 1673, 1223, 773K as function of composition were also investigated. It is found that the point defect concentrations change drastically for off-stoichiometric compounds. The main structural defects are preferably Mo vacancies or Si anti-structure atoms on the Mo sublattices in Si-rich alloy, and Mo anti-site in Mo-rich alloy, respectively. According to the calculated effective formation enthalpies of point defects, the effective formation enthalpies from big to small in sequence are Mo anti-site, Si anti-site and vacancy (Mo and Si). This result suggests that the vacancy, especially for Si vacancy, is a main type of point defect in C11b MoSi2 system.