Growth and Property Characterization of Relaxor Ferroelectric PZN-PT Single Crystals

Abstract

Relaxor ferroelectric single crystals Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) are touted as the next generation materials for high-performance piezo devices and systems including underwater acoustic sensors/actuators, ultrasound medical imaging probes, force/pressure sensors etc. Compared to state-of-the-art lead zirconate titanate (PZT) ceramics, these single crystals exhibit superior dielectric and piezoelectric properties, with dielectric constant: KT a?Y 5000, piezoelectric coefficients: d33 = 2000 pC/N, and electromechanical coupling factors: k33 a?Y 0.94. In this project, an improved high-temperature flux growth technique was used to grow PZN-PT single crystals. The results show that by controlling the isotherms in the solution, high homogeneity single crystals can be produced. The effect of crystal composition, orientation, domain structures, and the poling conditions on dielectric, piezoelectric and electromechanical properties of PZN-PT single crystals are investigated. It is observed that for [001]-poled crystals, the dielectric and piezoelectric properties are sensitive to the composition whereas it is not so for the coupling factors. The results further show that [011]-poled single crystals exhibit exceptionally large transverse piezoelectric coefficients with d32 a?? -(3000-4000) pC/N for the composition close to the MPB. This is due to poling induced monoclinic and/or orthorhombic phases which, when exist in appropriate quantity, are responsible for the superior dielectric and electromechanical properties observed. However, when present in sufficient quantities, they cause abrupt property degradation; a phenomena known as a??Overpolinga??. This work also presents the detailed characterization of transverse, longitudinal and shear properties of [111]-poled single-domain, [001] and [011] multi-domain PZN-PT single crystals using the resonance technique. Using coordinates transformation, the single-domain data of [111]-poled single crystals are used to deduce the material constants of [001] and [011]-poled multi-domain crystals. The discrepancy between the measured and deduced values of multi-domain crystals are compared and discussed. Finally, based on the findings of the present work, possible reasons for large scatters in the reported properties of these relaxor single crystals are discussed. The property matrices generated for differently poled PZN-PT single crystals in the present work can be directly used for the device design.