Measurements Along the Growth Direction of PMN-PT Crystals: Dielectric, Piezoelectric, and Elastic Properties

Property measurements are reported for Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) single crystals grown along (001) by a seeded-melt method. Chemical segregation occurs during crystal growth, leading to property changes along the growth direction. Variations in dielectric, piezoelectric, and elastic properties were evaluated for specimens selected from the crystals. Room-temperature data are correlated with T_C and composition that ranged from 27 to 32% PT, i.e., in the vicinity of the morphotropic phase boundary (MPB). While there was little change in the high electromechanical coupling factor k₃₃ (0.87-0.92), both the piezoelectric charge coefficient d₃₃ (1100-1800 pC/N) and the free dielectric constant K₃₃ ^T (4400-7000) were found to vary significantly with position. Increases in d₃₃ and K₃₃ ^T were relatively offsetting in that the ratio yielded a relatively stable piezoelectric voltage coefficient g₃₃ (27-31 times 10^-3 Vm/N). Values are also reported for the elastic compliance (3.3-6.3 times 10^-11 m²/N) determined from resonance measurements. Enhancements in d₃₃ and K₃₃ ^T were associated with lattice softening (increasing s₃₃ ^E) as the composition approached the MPB. Details are reported for the piezoelectric, dielectric, and elastic properties as a function of growth direction, T_C, and composition. The results are useful for an understanding of properties in PMN-PT crystals and for the design of piezoelectric devices.