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

• The point defects of C11b MoSi2 were studied systematically.
• MoSi2 is semimetallic with strong directional covalent bonds.
• Some rules of the point defect concentrations were revealed.
• Vacancy is a main type of point defect in MoSi2.

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, 773 K 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.