High-Performance Piezoelectric Single Crystals of Complex Perovskite Solid Solutions
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Piezoelectric Single Crystals of Complex Perovskite Solid Solutions Zuo-Guang Ye
Abstract Relaxor-based single crystals of complex perovskite solid solutions, Pb(Mg1/3Nb2/3)O3 –PbTiO3 [PMN–PT] and Pb(Zn1/3Nb2/3)O3–PbTiO3 [PZN–PT], exhibit extraordinary piezoelectric performance, with extremely high piezoelectric coefficients, very large electromechanical coupling factors, and exceptionally high strain levels. These materials outperform the currently used Pb(Zr1−xTix)O3 [PZT] ceramics, making them the materials of choice for the next generation of electromechanical transducers for a broad range of advanced applications. In this article, recent major advances in the development of piezocrystals are reviewed in terms of crystal growth, piezoelectric properties, crystal chemistry, domain structure, and device applications.
Introduction Piezoelectrics can sense environmental mechanical forces by giving out electric signals and can generate mechanical responses when driven by electric forces. They have found applications in a wide range of electromechanical sensors, actuators, and transducers that are important in various fields, such as medical ultrasonic imaging, diagnostics and therapy, sonar, industrial and laboratory process control, micro-/nano-positioning, environmental monitoring, information processing, and telecommunication. As the range of applications continues to grow, so does the demand for new materials with improved piezoelectric properties. The performance of a piezoelectric is mainly measured by its (1) piezoelectric coefficients (dij) that relate polarization Pi (or strain) developed with stress σj (or electric field) applied (i.e., Pi = dijσj, [i = 1, 2, 3; j = 1, 2, . . . 6]); (2) electromechanical coupling factors (kij) that measure the efficiency of electromechanical energy conversion; and (3) strain level that determines acoustic source power and actua-
tion strength. Figure 1 depicts the history of the development of piezoelectric materials in terms of piezoelectric coefficient d33 (meaning that the piezoreponse occurs in the same direction as the drive, P3 = d33σ3).1 The piezoelectric coefficient d33 is the most commonly used one in practical applications over the years. The milestones are marked by the discoveries of BaTiO3 in the 1940s and Pb(Zr1−xTix)O3 (PZT) in the 1950s. For almost 50 years, PZT-based systems have been the most widely used piezoelectric materials; however, their piezoelectric performance has only improved slightly over this time. A breakthrough occurred in the late 1990s when Park and Shrout2 reported, following an earlier work by Kuwata et al.3, that single crystals of the solid solutions between relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) or Pb(Zn1/3 Nb2/3)O3 (PZN) and ferroelectric PbTiO3 (PT), (1−x)PMN–xPT (PMN–x100%PT) and (1−x)PZN–xPT (PZN–x100%PT), with compositions near the morphotropic phase boundary (MPB), could exhibit very high
MRS BULLETIN • VOLUME 34 • APRIL 2009 • www.mrs.org/bulletin
piezoelectric coefficients (d33 > 2,000 pC/N), extremely large strain
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