Dielectric loss as an indication of the kinetics of the ferroelectric phase transition

The dependences tanδ( f, T ) for triglycine sulfate and diglycine nitrate single crystals are investigated in the frequency range f = 1−2 × 10 7 Hz at temperatures from −150 to 50°C for triglycine sulfate and from −150 to −60°C for diglycine nitrate. The results are discussed in the framework of the model according to which two or more types of media with different dielectric properties are formed in the ferroelectric phase. The polar volumes of domains themselves and the volumes of domain walls with different symmetries are treated as individual media. The dependences tanδ( f, T ) make it possible to separate the contribution of a particular medium and to trace its evolution with temperature. The results of the analysis of the relaxation properties confirm that the phase transitions lead to the formation of two media (the polar medium and domain walls) in triglycine sulfate and three media (the polar medium and two types of domain walls) in diglycine nitrate. It is demonstrated that the relaxation properties are not steady-state characteristics of the samples but depend on their prehistory.