Analysis of thermoelastic properties of NaF and MgO at high pressures and high temperatures

We present an analysis of thermoelastic properties such as thermal expansivity , isothermal bulk modulus, its pressure derivative and Anderson-Grüneisen parameter for NaF and MgO solids at high pressures and high temperatures. The Holzapfel adapted polynomial of second order (AP2) equation of state (EOS) has been used to predict pressure-volume-temperature (P-V-T) relationships, and for the solids under study up to their phase transition pressures. Volume dependence of has been considered to be similar to that for the Grüneisen parameter formulated by Burakovsky and Preston (B-P). The results for and have been obtained using the B-P model at different values of volumes and pressures along isotherms at selected temperatures. The results for and are found to compare well with the available experimental data. Values of decrease rapidly in the lower pressure region and become virtually constant at high pressures and high temperatures. We have discussed the role of anharmonic character of solids responsible for this behaviour. Variations of the product with P and T are also estimated and interpreted using a thermodynamic identity. It is found that the assumption for constant used in previous studies is only approximately correct.