Specific heat of NH4Br and NH4BrxCl1−x crystals close to the antiferroelectric transition

Abstract

We calculate the specific heat CVI of NH4Br and mixed crystals of NH4BrxCl1−x using the Ising model for the transition between the disordered (D) and antiferro- (AF) electric phases in these crystalline systems. Our CVI values, which we calculated for xBr=1, 0.26, and 0.51 are in good agreement, both below and above TC, with the observed CP data from the literature. Our value of ɑ≅0.1 (T<TC and T>TC) for the critical exponent of the specific heat agrees with the value of 0.125 predicted by a three-dimensional Ising model.