Heat Transfer in Ferroelectrics

By measuring the thermal conductivity and thermal diffusivity of ferroelectrics, the processes of polar bonds self-ordering and changing in this ordering by the bias electrical field have been studied. In polar crystals, the transfer of thermal energy is significantly hindered, since the acoustic phonons, responsible for thermal energy transfer, interact with the optical phonons. As a rule, such an interaction retards heat transfer due to additional contribution to phonon scattering process, which is revealed by the deep minimum of diffusivity. However, it was found that the optical-acoustic interaction can increase thermal diffusion, which is expressed as a large and sharp maximum diffusivity in the antiferroelectrics, in which the soft phonon mode disappears in the middle of the Brillouin zone, since their phase transition occurs with a multiplication of lattice unit cell. In this case, therefore, the optical phonons are actively mixed with acoustic ones, participating in heat transfer.