Effect of Processing on the Microstructure and Properties of Lead Magnesium Niobate-Lead Titanate Single Crystals Grown by Seeded Polycrystal Conversion

Adam M. Scotch*, Ceramics Division, Materials Science and Engineering Laboratory
Martin P. Harmer and Helen M. Chan, Department of Materials Science and Engineering, Lehigh University

Recent measurements have demonstrated that single crystal ferroelectrics exhibit dramatic improvements in the electromechanical properties compared to their conventional polycrystalline ceramic counterparts. For example, single crystals of the relaxors Pb(Mg1/3Nb2/3)O3 (PMN) or Pb(Zn1/3Nb2/3)O3 (PZN) with PbTiO3 (PT) in solid solution possess electric-field induced strains > 0.6 %, longitudinal coupling coefficients k33 > 90 %, piezoelectric coefficients d33 > 1200 pC/N, and dielectric constants from 1000 to 5000 with low dielectric loss.  Consequently, there exists great potential for these single crystal materials to be incorporated into existing devices such as ultrasonic transducers and actuators.  The single crystal properties can be exploited for a broad range of applications including naval sonar and medical ultrasonics.

Single crystals of PMN-PT have been produced via the Seeded Polycrystal Conversion [SPC] technique. Polycrystalline precursors of PMN-PT are converted to single crystals by inducing the boundary of a seed crystal to migrate through a polycrystalline matrix. The quality of PMN-PT single crystals grown by SPC is directly influenced by the microstructure of the polycrystalline precursor. The goal of this work was to examine the factors that controlled the final microstructure of the matrix and grown single crystals and to characterize their effects on properties. Specifically, the roles of sintering atmosphere, PbO liquid phase, and seed crystal orientation will be presented. It will be shown that by optimizing the processing parameters of the SPC process, transparent single crystals can be produced with maximum strain values of 0.72 % at 46 kV/cm, d33 = 2180 pC/N, and room temperature dielectric constants of about 5300 for poled <001> oriented crystals of PMN with 30 % mole fraction PT.