Abstract
We apply first-principles calculations to study the influence of pressure on the structure, elastic modulus, hardness, brittle-or-ductile behavior and melting point of NbSi2. Four NbSi2 phases: C40, C11b, C54 and C49 are considered based on the structural feature. The results show that the calculated formation enthalpy of the four NbSi2 phases is negative within the pressure range of 0–60 GPa, indicating that they are thermodynamically stable in whole pressure. In particular, the calculated formation enthalpy of the C54 NbSi2 is smaller than the other NbSi2 phases, indicating that the C54 NbSi2 is more thermodynamically stable than the other NbSi2 phases. The calculated elastic modulus and Vickers hardness of NbSi2 increase with increasing pressure. Note that the pressure results in brittle-to-ductile transition of the C40 NbSi2, C11b NbSi2 and C54 NbSi2 between 30 GPa and 60 GPa. Naturally, the increasing of mechanical properties is that the pressure enhances the electronic hybridization between Nb and Si, which is demonstrated by the chemical bonding such as Nb–Si bond and Si–Si bond.
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