Advances in Manufacturing Relaxor Piezoelectric Single Crystals

Relaxor piezoelectric single crystal, lead magnesium niobate-lead titanate (PMN-PT), has potential to greatly improve both piezoelectric actuator and transducer applications. High-quality PMN-PT single crystals with the diameter over 50 mm have been successfully grown along different crystallographic directions by the Bridgman technique at TRS. As a solid solution system, PMN-PT inevitably exhibits an inhomogeneous composition distribution along the boule in conventional Bridgman growth, which results in the variation of dielectric and piezoelectric properties along the growth direction and limits the useful portion in each crystal boule. Zone melting growth technique has been developed to further increase the composition uniformity in solid solution PMN-PT crystal. By using zone-melting growth technique, PMN-PT crystals with 22-25 mm in diameter and 150 mm long have been grown at TRS. This paper reviews the progress in Bridgman and zone-melting growth of PMN-PT with the emphasis on uniformity improvement. In addition, TRS recently developed new piezoelectric crystals with modified PMN-PT compositions, which have expanded operating temperature ranges to 120degC and coercive field to 5 kV/cm. Since these new materials were grown directly from the melt by the Bridgman technique, commercialization is achievable by applying the well established crystal growth process for PMN-PT.