Thermodynamic Properties Of XTiO₃and XZrO₃（X=Ca、Sr And Ba） By The Ortical Calculations

The lattice constants, elastic constants, electronic structures and thermophysical properties of perovskite XTiO3and XZrO3(X=Ca、S、Ba)have been investigated using first-principles calculations based on the density function theory. The calculated lattice constants agree well with the experimental value and other theoretical calculations. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and anisotropic ratio are also evaluated from the calculated single crystal elastic constants. The calculated results indicate that SrTiO3, BaTiO3and BaZrO3with perovskite are brittle and CaTiO3, CaZrO3and SrZrO3are ductility according to the value of B/G And CaZrO3is ductility than others; BaTiO3is more brittle than others. The calculated band structures indicate that perovskite XTiO3and XZrO3(X=Ca、 Sr and Ba) are indirect semiconductors. The results show that the energy band gaps decrease with increasing cation mass. The heat capacity and thermal expansion vary with temperature and pressures are also obtained using quasi-harmonic Debye model. For all the XTiO3and XZrO3, the heat capacity, bulk modulus, thermal expansion coefficient, Gibbs free energy and volume vary with temperature and pressures similarly. The heat capacities increase quickly with the change of the temperature and pressure in the range from0K to500K; the coefficients of thermal expansion increase quickly with pressures at high temperature. Gibbs free energy, bulk modulus B and volume increase quickly with pressures at low temperature.