POLARIZATION CHANGES IN THE FERROELECTRIC RELAXOR LEAD MAGNESIUM NIOBATE

A study is reported of the polarization and depolarization processes i n the model ferroelectric relaxer, lead magnesium niobate (PMN), in pu lsed and sine electric fields applied along the pseudocubic direction (001) above T-d (T-d is the phase transition temperature between the i nduced macrodomain ferroelectric and the nonpolar phases). The study w as made by the electroluminescence and polarization-switching current hysteresis techniques. Pulsed electric-field measurements revealed the influence of pulse duration on electroluminescence intensity under po larization and depolarization of a sample, as well as a decrease of de lay in the onset of depolarization for pulses shorter than the time re quired for the polarization to set in. A delay of depolarization in a sine electric field was observed to exist within a certain instantaneo us field-strength interval. A study has also been made of the increase of the depolarization delay induced by simultaneous application of a sine electric field and a de bias, or of;ln axial mechanical stress va rying in phase with the electric held. The results obtained indicate t he onset and persistence of held-induced local ferroelectric regions w ithin a certain interval of instantaneous electric-held strengths. The effect of domain and domain-like processes on these phenomena is disc ussed.