First Principles Calculations on Elastic, Thermodynamic and Electronic Properties of Co2Zr and Co2Ti at High Temperature and Pressure

Co2Zr and Co2Ti are both cubic crystals with a Cu2Mg-type structure. The elastic, thermodynamic and electronic properties of the intermetallic compounds Co2Zr and Co2Ti are investigated by using ab initio plane-wave pseudopotential density functional theory (PWPDFT) and generalized gradient approximation (GGA) under high temperature and pressure. The partially calculated results are consistent with the available experimental data. The elastic properties of Co2Zr and Co2Ti under high pressure were first studied by first principles calculations. The results indicate that the elastic constants, elastic modulus and Poisson's ratio are functions of pressure, indicating that the effect of pressure on the ductility and anisotropy is significant. The thermodynamic properties are also calculated by the quasi-harmonic Debye model. In the range of 0 similar to 100 GPa pressure and 0 similar to 1500 K temperature, the Debye temperature Theta, the heat capacity C-V and the thermal expansion alpha vary with pressure and temperature. Co2Ti has a higher Debye temperature than Co2Zr under the same pressure. Decreasing temperature and increasing pressure have the same effects on C-V and alpha. The electron density difference and density of states of Co2Zr and Co2Ti are finally investigated. The results show that both Co2Zr and Co2Ti are typically metal crystals but Co2Zr has greater covalence than Co2Ti.