PMN-PT crystal of less defects and more uniformity

3 inch lead magnesium niobate - lead titanate (PMN-PT) crystal ingots are successfully prepared using Vertical Gradient Freeze (VGF) method. Compared with the traditional Bridgman method, VGF method is expected to give higher yield and lower defects due to sufficient agitation and less thermal shock. As a result, [001] grown and poled PMN-PT crystals typically have electromechanical coupling coefficient k₃₃ higher than 0.91, suitable for medical ultrasound imaging applications. Rhombohedral-tetragonal phase transition temperature is measured around 90°C and Curie temperature is measured over 125°C as typical imaging-grade crystals. Adequate agitation during growth also enhances in-wafer property uniformity. Variation coefficients for in-wafer free relative permittivity and electromechanical coupling coefficient k_t is measured at 2% and 1%, respectively.