A method has been developed to obtain an equation of state for ionic solids starting from the theory of interionic potentials and using analytical functions for the volume dependence of the short-range force constant. The expressions are also obtained for isothermal bulk modulus and its pressure derivatives. Numerical analysis is presented for a NaCl crystal up to 30 GPa. The results are compared with the available experimental data. The variation of the pressure derivative of bulk modulus with pressure has also been studied using the formulation recently developed by Stacey.

We calculate the variation of thermal expansivity α with pressure for MgO at high temperatures, in the range 300–1800 K, using: (a) the thermodynamic formulation developed by Guillermet within the framework of Murnaghan's approximation, and (b) the Anderson-Isaak equation representing the variation of α with compression along isotherms. The results obtained from the two methods are compared and discussed. The AndersonIsaak equation is found to yield more consistent results.

The Grüneisen theory of thermal expansion as formulated by Born and Huang has been modified by including higher-order terms for the change in volume in the expansion of potential energy. New expressions are obtained for the thermal expansivity and bulk modulus, and used to estimate these quantities for MgO and other minerals in the temperature range 300–1800 K. The results are found to present close agreement with the experimental data.

The Chopelas-Boehler approximation for the volume dependence of the Anderson-Gruneisen parameter and the Anderson formula for the temperature dependence of thermal expansivity have been used to study the pressure-volume-temperature relationship for LiF, NaF and CsCl crystals up to a pressure of 90 kbar and in the temperature range 298–1073 K. The results obtained are found to present close agreement with the available experimental data.