Thermal properties at the commensurate-incommensurate transition of K2ZnCl4

Abstract

The heat capacity of the K2ZnCl4 single crystal was measured between 330 K and 415 K using an adiabatic calorimeter. A distinct anomaly of the commensurate-incommensurate transition was observed at 403.64 +/- 0.05 K for the first time by the adiabatic calorimetry, where the enthalpy change is Delta H = 9.990 J . mol(-1) and the entropy change is Delta S = 0.025 J . K-1 mol(-1) . The anomaly of the heat capacity is demonstrated by the behavior of the phase soliton or the domain wall near the transition point. The heat capacity was simulated numerically by using the phenomenological Landau theory and compared with the experimental results. The anomaly of the thermal expansion near T-C measured by TMA is related with a structural phase transition accompanied by the entropy change. We discuss the influence of the anomalous change of the thermal expansion compared with the heat capacity near T-C.