Specific heat of crystalline ferroelectrics at low temperatures

The specific heat of various pure, crystalline ferroelectrics—LiNbO3, LiTaO3, NaNO2, BaTiO3, TGS—has been measured between 0.5 K and 40 K. For all samples we observe a pure Debye's T3-dependence of the heat capacity as expected for the low temperature limit (T < θ0D/50). No excess heat capacity could be detected. In contrast to earlier results the calculated Debye temperatures, θ0D, are in excellent agreement with values deduced from elastic constants. Possible origins of previously reported excess heat capacities in numerous ferroelectrics are discussed; it is strongly suggested that these excess heats result from the presence of statistically distributed dipolar defects.