Electromechanical properties of high- coupling (1-ξ)Pb(Zn1/3Nb2/3)O3-(ξ)PbTiO3 single crystals for sound projectors

Isothermal weak field frequency sweeps were conducted over the temperature range 30 to 140°C on multidomain, oriented, and poled (1-x)Pb(Zn_1/3Nb_2/3)O₃-xPbTiO₃ (PZN-PT) single crystals with x = 0.045, 0.06, 0.07, and 0.08 near the ferroelectric rhombohedral (F_R)-ferroelectric tetragonal (F_T) morphotropic phase boundary (MPB). The temperature dependencies of the small-signal 33-mode electromechanical properties were derived from the isothermal frequency sweeps. Morphotropic compositions with x = 0.06 and 0.07 PT were found to exhibit the largest electromechanical coupling and piezoelectric coefficient, with k₃₃ > 0.90 and d₃₃ ~2300 pC/N, and the lowest short-circuit Young´s modulus of ~9 GPa. Reversible zero-field elastic instability attributable to a F_R-F_O transition was observed under isothermal compression-decompression of a 0.94PZN-0.06PT single crystal. The application of a dc bias field enhanced the F_R stability under compression. The large-signal, dc biased, 33-mode electromechanical response was measured under mechanical compressions similar to those used in sound projectors. The remarkable small-signal electromechanical properties are in a good agreement with the large-signal response. The crystal response to thermal, electrical, and mechanical variable is discussed in terms of high-coupling single crystal models.