Specific heat study at the commensurate - incommensurate transition of K2ZnCl4

Abstract

The heat capacity of the K2ZnCl4 single crystal was measured for the first time using adiabatic calorimetry [1] between 330 K and 415 K. A distinct anomaly with H = 9.99 J . mol(-1) and S = 0.025 J . K-1. mol(-1) showed up at 403.643 +/- 0.001 K revealing the commensurate - incommensurate (C - INC) transition so-called lock-in transition. Due to small change of the entropy around this transition no anomaly in the heat capacity was measured by a.c. calorimetry [2]. The anomaly of the heat capacity due to lock-in transition shows a sharp increase below T-C, and decreases gradually above T-C, whose shape is consistent with one of the discommensuration picture of the phase soliton. We also discuss the prospective relationship between the transition enthalpy and the temperature range of INC phase.