Influence of cyclic phase transitions on some properties of the ferroelectric perovskites

The results of investigations of the influence of cyclic phase transitions on certain properties of the ferroelectric perovskites are presented. The materials were PZT-type ceramics obtained either by hot-pressing or by classical ceramic technology. It has been found that a close relationship exists between the concentration of linear defects and the stability of the resonant frequency as a function of temperature and time. The investigated samples can be divided into two groups: samples with high initial stability of resonance frequency and samples with low initial temperature stability. Our investigations show that in this two cases it is possible to distinguish three ranges of numbers of thermocycles, but the dependencies in the two cases differ one from the other. The change of concentration of defects and their distribution inside the crystallites lead to changes of temperature stability of resonant frequency. After 5–6 thermocycles the stability increases, but if the initial stability of the resonant frequency is high the changes are too small for practical applications.