Low temperature behavior of heat capacity and thermal conductivity in crystalline ferroelectric materials

There is a great deal of confusion as to the very low temperature behavior (below = 5 K) of the heat capacity and thermal conductivity in ferroelectric materials. We show that actually they fall into two classes: Those with crystal-like (Debye-like) thermal properties and those that display glass-like excitations. Furthermore, there is an exact correspondence between the materials with glass-like excitations at low temperature and those that display both a diffuse ferroelectric transition at Tc and anomalous index of refraction, n(T), above Tc. © 1985 The Japan Society of Applied Physics.