Property uniformity and poling behavior of PMN-PT crystal grown by vertical gradient freeze method

Abstract

3-Inch diameter PMN-PT ingots were grown along [001] direction using Vertical Gradient Freeze (VGF) method. Wafers are sliced, sequentially numbered and tested for the study of property distribution along the ingot, and samples from the same wafer were studied for in-wafer uniformity. As a result, [001] grown and poled PMN-PT crystals typically have electromechanical coupling coefficient k33 higher than 0.91, and free relative permittivity between 4,600 and 7,500, varying monotonically along the ingot, due to PT composition segregation. In-wafer free relative permittivity variation coefficient is measured within 2%, due to sufficient agitation during growth. It is also 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). It is thought that over-poling is a field-induced phase transition and such transition is found reversible by annealing at certain elevated temperatures.