Thermodynamic properties of calcium ferrite-type MgAl2O4: A first principles study

Abstract

The diamond anvil cell experiments have revealed that the calcium ferrite (CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt (MORB) in the lower mantle. In this study, we have performed first principles lattice dynamics calculations for the MgAl2O4 end-member of the aluminous phase based on density functional perturbation theory using two functionals within the local density approximation (LDA) and generalized gradient approximation (GGA) for bracketing the calculated properties at their lower and upper limits, respectively. A simple empirical pressure correction at zero temperature has been applied to both LDA and GGA. The results of room-temperature equation of state (EOS) and zero-pressure thermal expansion calculated by GGA with pressure correction have shown the best agreement with available experimental data. The high-pressure and temperature thermodynamic properties have been obtained using the GGA with correction method. The pressure-volume relations are fitted with a third-order high-temperature Birch-Murnaghan EOS. The isobaric heat capacity, the coefficient of thermal expansion and isothermal bulk modulus are fitted with polynomials and their coefficients are reported in the range of 0–40 GPa and 300–2000 K. The density profile of MORB estimated using the computational thermo-elastic constants supports the hypothesis that the subducted oceanic slabs could gain enough downwelling forces into the lower mantle.