Over-poling Study of PMN-PT and PIN-PMN-PT Crystal Grown by Vertical Gradient Freeze Method

3 inch Lead magnesium niobate - lead titanate (PMN-PT) crystal was grown by Vertical Gradient Freeze (VGF) method. Poling reactions of [001]-poled PMN-0.29PT and PMN-0.31PT were studied. DC field 50 similar to 1500 V/mm were used to pole along [001] direction, dielectric constant, plate mode coupling coefficient and dielectric loss were recorded. It is shown that piezoelectric properties saturate around 350 kV/mm for PMN-0.29PT and 250 kV/mm for PMN-0.31PT, respectively. Both PMN-0.29PT and PMN-0.31PT experience property degradation due to over-poling over 1300 kV/mm, and PMN-0.31PT is more susceptible to over-poling due to closer vicinity to the Morphotropic Phase Boundary (MPB). The mechanism of over-poling is analyzed by observing dielectric constant against temperature in zero field heating (ZFH) environment. Compared to optimized poled samples, over-poled samples lack rhombohedral-to-tetragonal phase transition, which confirms that over-poling is a field-induced phase transition. Furthermore, over-poling is found reversible by annealing at elevated temperatures. In the case of PMN-0.29PT, over-poling could be reversed by annealing at 300 degrees C for 1 hr. Such discovery could serve as potential remedy for over-poled PMN-PT crystals, although a more comprehensive study must be carried out to verify microscopic phase change and macroscopic property restoration before and after annealing. Above all, it is recommended to impose a DC poling limit of 1000 V/mm anytime for [001] oriented PMN-PT to avoid over-poling. Similar study is to be carried out on PIN-PMN-PT tertiary crystal system.