Heat Transfer in Polar Crystals

Thermal conductivity is very important technical parameter of electronics materials, which include polar crystals. Heat transfer in them is provided by short lattice waves with low velocity, so polar crystals looks like turbid medium. It was found that phonons interaction is determined polar-sensitive bonds, which is commensurable with crystal lattice parameter. Polar-sensitive (mixed ionic-covalent) bonds strongly affect the processes of heat transfer of crystals: their thermal conductivity is much less than that in the purely-ionic or purely-covalent crystals. Anomalies of thermal diffusion in the vicinity of ferroelectric phase transitions are also studied, when ordered polar structure spontaneously changes to disordered non-polar structure. In ordered phase the thermal diffusion coefficient increases; this fact indicates that disordering of polar-sensitive bonds hinders diffusion of heat.