关键词: 密度泛函理论, 镁铝尖晶石, 相变, 力学稳定性

Abstract: The equations of state, thermodynamically formed enthalpy and mechanic properties of the three phases of MgAl2O4 oxides under 50 GPa were presented via the pseudowaves plane (PWP) approach based on density functional theory (DFT). The calculated results showed that according to the state equations the transition pressures under which the MgAl2O4 spinel was transformed into CaFe2O4-type MgAl2O4 CF-phase and then into CaTi2O4-type MgAl2O4 CT-phase are 26.79 GPa and 30.19 GPa, respectively, and the differences between the calculated and tested values are +0.79 GPa and -11.81 GPa, respectively. With the thermodynamically formed enthalpy in combination with GGA, the CF-phase transition pressure is 24.52 GPa, while the CT-phase transition pressure is 39.85 GPa if combined with LDA, i.e., the comparative errors are -1.48 GPa and -2.15 GPa, respectively. It was found that the mechanical structure of spinel are unstable under the pressure over 30 GPa. But, in case the spinel phase is under the other two high pressures as above, its mechanical properties are stable if the pressures are in the range that has already been taken into account.