Calculations of the High Pressure Phase Transition Point of NaCl, KCl and NaF Crystals

By using the theory of lattice dynamics, the Gibbs free energies of NaCl, KCl and NaF crystals were calculated for both NaCl and CsCl structures. Results show that the large, attractive short-range interaction between the second neigbour ions may play an important role in the explanation of the relative stability of NaCl and CsCl structures. By using the potentials obtained from Gordon-Kim model, the pressure of phase transition and the lattice constants were calculated. Results are satisfactory. The effect of temperature on the phase transition point is also investigated. The result shows that the shift in the transition point is very small when temperature changes.