Analysis of the Specific Heat and the Free Energy of [N(Ch 3 ) 4 ] 2 Znbr 4 Close to the Ferro-Paraelastic Phase Transition

Abstract

A power-law formula deduced from the Ising model was used to analyze the temperature dependence of the specific heat C p and the Gibbs free energy G of [N(CH 3 ) 4 ] 2 ZnBr 4 compound in the vicinity of the phase transition temperature of T C = 287.2 K. Obtained values of the critical exponents α from the Gibbs free energy were consistent with that predicted from 2-d potts model (α = 0.3), while obtained values of α from the specific heat in both ferroelastic and paraelastic phases were consistent with that predicted from the mean field theory (α = 0) in the vicinity of the phase transition temperature. This is an indication of that [N(CH 3 ) 4 ] 2 ZnBr 4 compound undergoes a second order type phase transition. Also, the enthalpy (H) and the entropy (S) of this crystal were calculated in terms of the extracted values of the critical exponent in both ferroelastic and paraelastic phases.