Low-temperature calorimetric study of phase transitions in CuCrP2S6

The heat capacities of CuCrP2S6 have been measured at temperatures between 5 and 350 K. Three phase transitions were observed at 30.45, 154.96 and 185.92 K. The normal heat capacity was determined by fitting a model heat capacity function consisting of the Debye and Einstein functions and a correction term for the Cp–Cv difference by nonlinear least squares fitting. The phase transition entropies based on the phonon heat capacity thus determined were 4.1, 2.7 and 6.2 J K−1 mol−1 for the three phase transitions, respectively. The phase transition occurring at 30.45 K is of a magnetic origin arising from the chromium spin and the upper two phase transitions are due to positional disorder of the Cu+ ions. Interpretation of the transition temperatures and transition entropies in terms of atomic interactions is in progress and will be reported in due course.