The Strain Response of Lead Zinc Niobate-Lead Titanate Piezocrystals: Phase Transitions and Non-Linear Effects

Abstract

Single crystals of Pb(Zn 1/3 Nb 2/3 )O 3 -PbTiO 3 (PZN-PT) produce high levels of strains with large electromechanical coupling coefficients and they exhibit high dielectric permittivity. These properties make PZN-PT single crystals promising materials for transducer and actuator applications. The large strains in these materials are partly due to electric-field-induced rhombohedral–tetragonal phase transitions that are temperature dependent. We have studied the phase transitions in ⟨001⟩ oriented Pb(Zn 1/3 Nb 2/3 )O 3 -xPbTiO 3 single crystals for x = 4.5% and x = 8% by measuring the piezoelectric strains of the crystals as a function of applied electric field and temperature. We have used laser Doppler interferometry to make direct measurements of the strain responses of the two types of ⟨001⟩ and ⟨111⟩ oriented PZN-PT single crystals in the rhombohedral phase as a function of AC electric fields and DC bias fields. When the applied electric field exceeds a threshold value, the dielectric and piezoelectric constants become a function of the applied field, and hysteresis loops are observed. Our results show that a positive DC bias stabilizes the domain configuration in the crystals and increases the range of AC voltages over which the response is linear. The threshold field, at the onset of non-linearity, is found to have a linear relation with DC bias field in the field range investigated. Very large shear strains have been observed for crystals poled in the pseudocubic ⟨111⟩ direction with d 15 values in the neighbourhood of ∼5500 pC/N for PZN-4.5%PT and ∼7500 pC/N for PZN-8%PT.