Static and kinetic thermal properties of ferroelectrics in the phase transition region

Department of Physics, Moscow State University, Moscow 119899, Russia

We shall report the recent results of the comparative study of thermal properties (specific heat and heat conductivity) for a set of crystals with ferroelectric phase transitions. The general approach to the analysis of the specific heat anomalies in proper (DTGSe, LaBGeO₅), pseudoproper (Li₂Ge₇O₁₅, TSCC, DSP), incommensurate ((NH₄)₂BeF₄, Rb₂ZnCl₄, TMATC-Zn) and isomorphous ((CH₃NH₄)₅Bi₂Cl₁₁) phase transitions will be discussed including effects associated with inborn impurities and radiation-induced defectness.

Surprisingly the heat conductivity coefficient (HCC) peculiarities expose a great variety of anomalous behaviors at the transition point region. The available data for the most representative crystals will be analyzed and compared with our recent results obtained with a high resolution by the steady heat flow method. The diffused and sharp negative and positive anomalies were found at the transition point region as well as step-like and combination of them. It was shown that HCC anomalies are closely related to the nature of the phase transition (order-disorder or displacive), and the suitable interpretation for the experimentally observed HCC anomalies will be given. The qualitative description of the HCC behavior for the crystals with the displacive (soft mode) type transitions and new experimental data for the crystals with incommensurate phase will be presented and discussed.