Calculation of the Specific Heat for the II-III and II-IV Phase Transitions in NH4Br

H. Yurtseven；A. Mertoglu

Chinese Journal of Physics

39卷4期（2001 / 08 / 01）

349 - 356

英文

The specific heat CV I is calculated in this study using the prediction of an Ising model for the II-III phase transition at 0.05 GPa and for the II-IV phase transition at the pressures of 0.19, 0.99 and 2.1 GPa close to TC for the NH4Br crystal. The values of the critical exponent for the specific heat of NH4Br which we determine from our analysis, are close to the predicted values of 1/16 (T ＜ TC) and 1/8 (T ＞ TC) obtained from the 3d Ising model. Our calculated specific heat CV I agrees well with the experimental CP below TC in the antiferro-ordered (phase III) and ferro-ordered (phase IV) phases of NH4Br. Above TC (disordered phase II) there occur discrepancies between our calculated CV I and the observed CP for NH4Br.