First-principles calculations to investigate third-order elastic constant, anharmonicity and temperature dependent second elastic constant of thermoelectric materials Cu3MSe4(M = V and Nb)

The research on material‘s mechanics is critical in thermoelectric. Herein, we study the second(Cij), third(Cijk) order elastic constants, anisotropic and pressure and temperature dependent elasticity of Cu3MSe4(M = V and Nb) utilizing density functional theory. The elasticity of Cu3MSe4(M = V and Nb) is anisotropic. In addition, the calculated Cij suggests that these materials show relatively weak mechanical properties as thermoelectric device, and the ratio of bulk modulus(B) versus shear modulus(G) suggest that they are brittle. Cijk and pressure induced Cij reveal that Cu3NbSe4 has stronger anharmonic strength than that of Cu3VSe4. Finally, the thermal expansions are evaluated via quasi-harmonic approximation, and the temperature dependent elastic constants Cij indicate that Cu3NbSe4 has weak temperature dependent than that of Cu3VSe4. This research is dedicated to the design of thermoelectric devices and discovering novel thermoelectric materials with high performance in view of mechanical properties.