Pressure Dependence of Interatomic Separation and Thermal Expansivity for Alkali Halides and Periclase (MgO)

Abstract

In this paper, a new isothermal equation of state is developed based on an approximation for the volume dependence of the Anderson{Gruneisen parameter -T along isotherm. The values of interatomic separation r with the change of pressure for nine alkali halides and periclase were investigated with the help of the new isotherm equation of state. The compression data are used to predict the pressure dependence of the coe-cient of volume thermal expansion. The results are compared with the available experimental data and other theoretical results. The isothermal equation of state (EOS) gives us valu- able information about the change in volume under the in∞uence of pressure at a flxed temperature and is thus re- lated to the compression of solids. The theoretical studies of EOS at high pressure are of wide importance because they help us in planning future high pressure experiments and are also important in comparing static high pressure experiments with shock wave experiments. If we have a phenomenological form of EOS, we can predict the high- -pressure properties and compression behavior of solids with a little efiort by determining the parameters from theoretical calculations or experimental data. Various forms of the isothermal EOS (1{5) have been made to predict correctly high-pressure behaviors, irrespective of the material. In this paper, we derive a new phenomenological EOS based on the approximation for the volume dependence of the Anderson{Gruneisen parameter -T along isotherm (6, 7). At the same time, we use it to calculate the values of interatomic separation r with the change of pressure. The compression data obtained in the present work have also been used to calculate the pressure dependence of the volume thermal expansion coe-cient. In order to examine the validity of presented isothermal EOS under study, we make a comparison of the calculated values and available experimental data as well as earlier theoretical investigations in the case of alkali halides and periclase. The method of analysis is given in Sect. 2. The sys- tematic comparison and discussion of the result are given in Sect. 3.