Experimental study of electric field influence on low-temperature,long-time relaxation in crystalline ferroelectrics

Calorimetric measurements with polycrystalline Pb_0.915La_0.085. (Zr_0.65Ti_0.35)O₃ were performed at liquid helium temperatures in an electric fieldE (0E4.3 kV/cm). Heat released after cooling fromT ₁ (1.3 K<T ₁35 K) toT ₀=1.3 K is very similar to that in amorphous metals and dielectrics. Experimental results disagree with the standard tunneling model. The observed heat release may be explained assuming the existence of a maximum energy _f in the distribution function. The maximum relaxation time _max was found as a function ofT ₁. A similar heat release is observed after switching on or off the electric field, independent ofT for 1.1 KT3 K, proportional toE ² with _maxE. No heat release was observed in the KH₂PO₄ single crystal.On leave of absence from the Technical University, Dresden, German Democratic Republic.On leave of absence from the Institute of Physics, Czechoslovak Academy of Sciences, Prague, Czechoslovakia.On leave of absence from the Central Institute for Solid State Physics and Material Research, Dresden, German Democratic Republic.