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

Taking Mo-Si compounds as model systems, we show that the coefficients of t hermal expansion (CTEs) of complex structures can be calculated precisely f rom first principles by incorporating the Debye model for acoustic response . Specifically, we obtain a nearly isotropic CTE in MoSi2 but a highly anis otropic CTE in Mo5Si3. The CTE anisotropy in Mo5Si3 is due to an elasticall y more rigid basal plane and a higher anharmonicity along the c axis. As th e structure of 5-3 compounds is modified from D8(m) to D8(l) by boron subst itutions (Mo5SiB2), we predict a significant decrease in the CTE anisotropy , which is confirmed by experiments.