An Isothermal Three-Parameter Equation of State Applied to Alkali Halide Crystals under High Pressures

From the definition of isothermal bulk modulus and an assumption of its relationship with the pressure, an isothermal three-parameter equation of state has been proposed, which is found to be applicable at high pressure. The proposed equation of state has been used to compute the pressure-volume behavior of NaCl crystal in the pressure range 0~30 GPa and CsCl crystal in the pressure range 0~40 GPa. The isothermal bulk modulus in the pressure range 0~30 GPa of NaCl crystal were also calculated. The results are in very good agreement with the experimental data. The pressure dependence of the isothermal bulk modulus BT and its first- and second-order pressure derivative are discussed, and the bulk modulus increases continuously with the increasing pressure and has a finite value as p.