Thermal expansion coefficients of Mo-Si compounds by first-principles calculations

Taking Mo-Si compounds as model systems, we show that the coefficients of thermal expansion (CTEs) of complex structures can be calculated precisely from first principles by incorporating the Debye model for acoustic response. Specifically, we obtain a nearly isotropic CTE in MoSi₂ but a highly anisotropic CTE in Mo₅Si₃. The CTE anisotropy in Mo₅Si₃ is due to an elastically more rigid basal plane and a higher anharmonicity along the c axis. As the structure of 5-3 compounds is modified from D8_m to D8_l by boron substitutions (Mo₅SiB₂), we predict a significant decrease in the CTE anisotropy, which is confirmed by experiments.