Thermal studies of the IV-III phase transition in CsZnPO₄

The single crystal of CsZnPO₄ (CZP) was synthesized by flux method, and the heat capacity was measured using an adiabatic calorimeter in the temperature range from 6 to 300 K. A heat capacity anomaly due to the IV-III phase transition was found around 220 K. The heat capacity anomaly becomes larger when the sample is cooled down to lower temperature, and annealed for longer time below the transition temperature. At 195 K, it takes about more than 100 h to transform the supercooled phase III into the low-temperature phase IV. The results of annealing experiments suggest that the III→IV phase transition proceeds with heterogeneous nucleation process.