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

Abstract

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 D8m to D8l by boron substitutions (Mo5SiB2), we predict a significant decrease in the CTE anisotropy, which is confirmed by experiments.