Abstract
We present results of first-principles local-density-functional calculations of the structural and elastic properties of Mo 5Si 3. Among the three different structures (D8 m, D8 8, and D8 l ), the D8 m structure (referred to as the T1 phase) has the greatest binding with a high heat of formation of −3.8 eV/formula unit. The bonding in Mo 5Si 3 is found to have pronounced covalent components, characterized by the planar Mo–Si–Mo triangular bonding units on the (001) plane and by the unusually short Mo–Mo bonds directly along the c-axis. The calculated six elastic constants of the D8 m structure are in excellent agreement with the experimental values. While the bonding in the (001) basal plane is stronger than the bonding along the [001] direction (i.e. C 11+ C 12> C 33 and C 66> C 44), the crystal anharmonicity is found to be higher along the [001] direction. The implication of our results on the anisotropy of thermal expansion coefficients is briefly discussed.
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