The pressure dependence of physical properties of La2Zr2O7: First-principles calculations and Quasi-harmonic Debye approximation

Abstract

The pressure_induced physical properties of La2Zr2O7 pyrochlore were investigated by local density approximation (LDA) theory combining with Quasi-harmonic Debye approximation (QHA). It has been shown that there is a linear increase in the molar Gibbs free energy with the increasing pressure and the value of molar Gibbs free energy is larger than zero when the pressure reaches a particular value. The calculated transformation pressure values are 0.35, 0.65, 1.81 and 3.35 GPa at the temperatures of 300, 500, 1000 and 1500 K, respectively. The calculated results show that the bulk modulus increases with the increasing pressure at a given temperature while decreases with increasing temperature at given pressure. The deviation between constant pressure heat capacity Cp and constant volume heat capacity Cv at different pressure is not sensitive at normal temperature. Analysis shows that lower thermal expansion coefficients at higher pressure results from the strong interaction among the atoms in compound.