[en] There are several ultrasonic techniques to measure the sound velocity, for example, the pulse-echo method. In such method, the size of transducer used to measure the sound velocity must be in the same order of the sample size. If not, the incompatibility of sizes becomes an error source of the sound velocity measurement. In this work, the Laser Induced Pressure Pulse (LIPP) method is used as ultrasonic method. This method has been very useful for studying the spatial distribution of charges and polarization in dielectrics. We take advantage of the fact that the method allows the sound velocity measurement, to study its variation as function of polarization state in (PZT) ceramics. In a sample with a known thickness e, the sound velocity ν is deduced from the measurement of the transit time T. The sound velocity depends on the elastic constants which in turn they depend on poling conditions. Thus, the variation of the sound velocity is related to the direction and the amplitude of the polarization.

[en] Usually to study the polarization reversal phenomenon, the applied field is varied gradually and the polarization is measured which give the hysteresis P–E loop. In many applications, such as in memory components, a fast switching (less than 100 ns) is required. For a fast switching the applied field must generally be of order 2E_C, where E_c is the coercive field. In this case the polarization is balanced between saturation polarizations + p_s and − P_s very quickly. Thus it is difficult to study the polarization reversal evolution. In this paper we have chosen to apply on poled PZT ceramic samples a depolarizing field slightly greater than the coercive field which permits a low polarization switching.