Evaluation of pressure and bulk modulus for alkali halides under high pressure and temperature using different EOS

Abstract

In the present work, the non-inverted (isothermal) type equations of state (EOS) which are based on interionic potential such as Vinet–Rydberg EOS, Shanker EOS, Bardeen EOS as well as Kumar isothermal EOS are used to study the variation of relative compression volumes in range 1–0.5 and the isothermal bulk modulus with high pressure at temperature T = 300 K for four alkali halides (NaF, NaCl, NaBr and NaI). The results for relative compression volume obtained from the four EOS have been compared with experimental data which indicated that up to 15 GPa they are in good agreement. But beyond this, the results which have been obtained from the Vinet–Rydberg EOS Shanker EOS and Bardeen EOS as well as from the experimental data showed that they are also in good agreement in the wide range of high pressure. While results obtained from Kumar isothermal EOS showed that beyond 15 GPa they deviated from the other EOS. Moreover the results of isothermal compressibility have shown that at the value 0.5, the calculated high pressures are equal to (170, 90, 78 and 60) GPa for NaF, NaCl, NaBr and NaI respectively. The results for the isothermal bulk modulus (KT) have been compared with four EOS and showed that the bulk modulus increases continuously with increase in pressure. The results indicated that up to 1 GPa are found to be in good convergence, but beyond this range, the results do diverge from each other for the four EOS. Finally, the variations of non-isothermal compression (inverted) and non-isothermal bulk modulus with high pressure have been investigated by using a non-isothermal Kumar EOS (Kumar General EOS).