HEAT-DIFFUSION CENTRAL PEAK IN THE DIELECTRIC SUSCEPTIBILITY OF FERROELECTRIC MATERIALS

Recently, low-frequency measurements (0.1-Hz region) of the elastic su sceptibility in KSCN near the order disorder phase transition at T-c=4 10 K revealed a relaxation that could be explained by entropy fluctuat ions. We present a phenomenological theory describing the heat-diffusi on central peak in the macroscopic (q=0) dielectric susceptibility. It results from the Landau free energy and the heat-diffusion equation. The model predicts a relaxation in the ferroelectric phase at low freq uencies that depends on sample size. It does not follow a simple Debye behavior, but reveals a long high-frequency tail.