Thermal diffusivity and critical behaviour of uniaxial ferroelectric Sn2P2S6

The anisotropy in the thermal diffusivity of uniaxial ferroelectric Sn2P2S6 has been measured as a function of temperature using ac photopyroelectric calorimetry. The second-order ferroelectric transition has been studied in order to ascertain the mechanisms which could explain the anomaly in specific heat through the study of the inverse of the thermal diffusivity. Landau model, as well as critical models considering the different roles of fluctuations of the order parameter and crystalline defects, are considered. Though in the ferroelectric phase the Landau model can mainly explain the anomaly in the physical properties, the fittings for the paraelectric phase show that it is necessary to take into account the influence of both fluctuations and defects to account for the results.