IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, . 58, . 9, SEPTEMBER 2011 1874 0885–3010/$25.00 © 2011 IEEE Electric-Field and Stress Effects on Depoling and Overpoling Phenomena in [001]-Poled Transverse Mode Pb(Zn 1/3 Nb 2/3 )O 3 - (6–7)%PbTiO 3 Single Crystal of [110] Length Cut Rahul Shukla, Leong-Chew Lim, and Prasanna Gandhi Abstract—Solid-solution Pb(Zn 1/3 Nb 2/3 )O 3 -PbTiO 3 (PZN- PT) single crystals, touted as next-generation piezoelectric materials, have been studied extensively in the past decade. This work addresses the advantages and limitations of trans- ducers made of transverse mode PZN-(6–7)%PT single crys- tals of [110] L × [001] T (P) cut. This cut exhibits superior elec- tromechanical properties, with k 31 ≈ 0.85 and d 31 ≈ -1450 pC/N, and an extremely high d s E 31 11 / value of >35 C/ m 2 . It also has relatively high overpoling, i.e., rhombohedral- to-tetragonal phase transformation, field of ≈2 kV/mm. This overpoling field further decreases with increase in axial com- pressive stress. Despite these good attributes, this crystal cut has a low depoling field of ≤ 0.3 kV/mm, a result of low coer- cive fields of [001]-poled relaxor-based single crystals, which decreases further with increasing axial compressive stress, lim- iting its bipolar drive capability. The axial compressive stress required to cause overpoling via rhombohedral-to-tetragonal phase transformation of relevant domain variants in the crystal is found to be >90 MPa. In contrast, this crystal cut depolar- izes at comparatively low axial tensile stress of ≈15 MPa, the magnitude of which is not significantly affected by the moder- ate forward field applied. I. I R  ferroelectric single crystals, notably Pb(Zn 1/3 Nb 2/3 )O 3 -PbTiO 3 [PZN-PT] and Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT), exhibit excep- tionally high dielectric and electromechanical properties with minimum hysteresis even when driven at relatively high applied electric fields compared with state-of-the-art lead zirconate titanate (PZT) ceramics [1], [2]. The prop- erties of these piezoelectric single crystals depend on both crystal composition and orientation. For instance, PZN- (6–7)%PT single crystals of [110] L × [001] T cut not only exhibit superior electromechanical properties, with k 31 ≈0.85 and d 31 ≈ -1425 pC/N, but also high d s E 31 11 / value of >35 C/m 2 [3]–[6], making it a suitable material for high-performance transducer applications. Note that d s E 31 11 / is a piezoelectric material parameter used in the blocking force expression of transverse (d 31 ) mode piezo- electric actuators [7]. During actual applications the piezo single crystals may experience an electric field, a mechanical stress, or a com- bination of both. The maximum applied electric field and mechanical stress are limited by the phase transformation and depoling characteristics of the single crystals. For ex- ample, the low coercive field of PZN-PT and PMN-PT single crystals is responsible for the low depoling field and limits its bipolar driving capability [8]. Phase transforma- tions in the relaxor single crystals have been reported at sufficiently high electric field and/or mechanical strains in variously oriented PMN-PT [9]–[15] and PZN-PT [12], [16]–[21] single crystals. The earlier works [9]–[21] were mainly concentrated on the effect of electric field and com- pressive stress on both longitudinal (d 33 ) and transverse (d 31 ) mode samples. The obvious reasons of interest in the compressive stress effect were the requirements for vari- ous applications, mainly under-water acoustic transduc- ers, and higher compressive strengths of the ceramics and single crystals. Furthermore, keeping longitudinal samples under high tension was either never required or quite im- practical for many of the applications. The current uses of transverse mode piezoelectric materials span from uni- morph actuators to the application of energy harvesting from ambient vibration, in which both high compressive and tensile stresses can be generated during the operation. This becomes more critical for ultra-sensitive PZN-PT single crystals. In this work, the effect of applied electric field and mechanical loading on the behavior of transverse mode PZN-(6–7)%PT single crystals of [110] L × [001] T cut have been investigated. Manuscript received December 31, 2010; accepted March 3, 2011. This work is supported by research grants received from the Ministry of Edu- cation (Singapore) and National University of Singapore, via research grant nos. R-265-000-221-112, R-265-000-257-112, R-265-000-257-731, and R-265-000-261-123/490. R. Shukla acknowledges the research schol- arship and technical support received from IIT Bombay and NUS for him to pursue his Ph.D. research. R. Shukla is with the Suman Mashruwala Advanced Microengineering Laboratory, Department of Mechanical Engineering, Indian Institute of Technology, Bombay, Mumbai, India, and the Department of Mechani- cal Engineering, National University of Singapore, Singapore. He is cur- rently with the Institute for Materials Research, School of Process Envi- ronmental and Materials Engineering, Faculty of Engineering, University of Leeds, Leeds, UK (e-mail: R.Shukla@leeds.ac.uk). L.-C. Lim is with the Department of Mechanical Engineering, National University of Singapore, Singapore, and Microfine Materials Technolo- gies Pte. Ltd., Singapore. P. Gandhi is with the Suman Mashruwala Advanced Microengineering Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, India. Digital Object Identifier 10.1109/TUFFC.2011.2026