Calculation of the Specific Heats for the II-III and II-IV Phase Transitions in NH₄I

This study gives our calculation for the specific heats C_VI due to an Ising model using the observed C_p data for the II-III and II-IV phase transitions in NH₄I. By fitting to the C_p data we determine the values of the critical exponent for the pressure of 0.14 GPa (II-III phase transition) and for the pressures of 0.75, 1.35 and 1.97 GPa (II-IV phase transition) in NH₄I. Our exponent values are close to the predicted values of the specific heat in a three-dimensional Ising model. Our calculated C_VI are in good agreement with the experimental C_p for NH₄I in most cases.