Analysis of isothermal equations of state for ionic solids and geophysical minerals at high temperatures

Abstract

We present an analysis of various isothermal equations of state (EOSs) such as the Birch-Murnaghan EOS, the Vinet EOS, the Shanker EOS, and the logarithmic EOS by studying the pressure-volume relationships, the isothermalbulk modulus K T , and its first pressure derivative KT for ionic solids such as NaCl, KCl, MgO, CaO and geophysical minerals such as MgSiO 3 perovskite at temperatures ranging from room temperature up to their melting temperatures under high compressions down to V/V 0 =0.6 where V 0 is the volume V at P=0. The results are compared with the corresponding values derived from the Hama-Suito EOS based on the augmented-plane-wave (APW) method and the quantum statistical model (QSM). The comparison reveals that the Vinet EOS and the Shanker EOS yield the closest agreement with the ab-initio results. At higher temperatures and higher compressions the values of P, K T , and K' T obtained from the Birch-Murnaghan EOS are somewhat higher and those obtained from the logarithmic EOS are lower than the values obtained from the Hama-Suito EOS. The results obtained in the present study compare well with the available experimental P-V-T data for MgO and MgSiO 3 .