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ezoelectric properties k33 and d33 of 0.67 Pb(Mg1/3Nb2/3)O3–0.33 PbTiO3 single crystals grown by a modified Bridgman method were measured in the temperature range of 20–150 °C. Recoverability of the properties after the samples were heated to 110 °C, above the ferroelectric–ferroelectric (F–F) phase transition temperature of the composition, was found. From 20 to approximately 80 °C, k33 increases slightly, while d33 is almost doubled. Between approximately 90 and 100 °C, k33 decreases sharply to roughly a level of PZT-5 ceramics and d33 decreases to about 700 pC/N. They increase again with further increase of temperature; at 140 °C they attain 0.74 and approximately 1300 pC/N, respectively, and then decrease quickly and approach zero at about 150 °C. When heating to 110 °C followed by cooling to room temperature, the property decay is small. After more than one dozen heating–cooling cycles, k33 and d33 tend to be stable at 0.89 and approximately 1220 pC/N, respectively. The results might be helpful for device design and applications of PMN–PT single crystals.

I. INTRODUCTION

Relaxor-based ferroelectric single crystals Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3– PbTiO3 (PMN–PT) have attracted considerable attention in recent years due to their extremely high piezoelectric properties.1,2 For PMN–PT, it was demonstrated by this group3,4 that large single crystals with high performance can be grown with the Bridgman method, indicating that the crystals can be produced on a certain scale. The high performance and availability of PMN–PT ferroelectric single crystals herald their wide applications for piezoelectric devices, such as ultrasonic transducers and actuators.5,6 Prototype medical ultrasonic probes made of PMN–PT single crystals have been demonstrated to have much wider bandwidth and higher sensitivity7 than corresponding ones made of PZT ceramics. Consequently, relaxor-based ferroelectric single crystals may lead to a “revolutionary improvement” for transducers. However, phase diagram8 and dielectric property studies of the PMN–PT system showed that there is a rhombohedral to tetragonal (R–T) phase transition below approximately 120 °C for PT contents of approximately 25–34 mol%, within which the more PT, the lower the R–T transition temperature. Recently Xu et al.9 found

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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 2, Feb 2003

http://journals.cambridge.org

Downloaded: 13 Mar 2015

that this phase transition is even more complex, for a monoclinic phase coexists with the rhombohedral phase. It is questionable whether or to what extent this phase transition influences the physical properties and applications of PMN–PT crystals. On the other hand, among PMN–PT solid solutions, crystals of 0.67 PMN–0.33 PT (PMN–PT 67/33) possess better dielectric and piezoelectric properties4 than other compositions at room temperature. Meanwhile, the transition temperature from the low-temperature phase to the tetragonal phase (L–T) is about 80 °C, lower