Sm doped PIN-PMN-PT crystals with diameter of 75mm and 100mm have been successfully grown in <001> orientation for the first time, which produced uniform (001) wafers large enough for medical ultrasound imaging transducer fabrication. Free dielectric permittivity of 75mm-diameter crystals reached 4900 – 6000, starting ~25% higher than the undoped PIN-PMN-PT crystals. The crystals also hold coercive field of 4.8 – 6.0kV/cm, similar to the undoped PIN-PMN-PT crystals, and Trt of 82 - 99°C, similar to PMN-PT crystals. These crystals may be the desirable alternatives to PIN-PMN-PT crystals for the medical ultrasound imaging transducers.

Short-range polar order in the relaxor ferroelectric material PbMg1/3Nb2/3O3-28%PbTiO3 (PMN-28PT) have been studied using neutron diffuse scattering. An external electric field along the [110] direction can affect the diffuse scattering in the low temperature rhombohedral/monoclinic phase. Diffuse scattering intensities associated with [110] short-range polarizations are partially suppressed, while those arising from [11¯0] polarizations are enhanced. On the other hand, short-range polar order along other equivalent 〈110〉 directions, i.e., [101], [101¯], [011], and [011¯] directions, are virtually unaffected by the field. Our results, combined with previous work, strongly suggest that most parts of short-range polar order in PMN-xPT relaxor systems are robust in the low temperature phase, where they couple strongly to ferroelectric polarizations of the surrounding ferroelectric domains, and would only respond to an external field indirectly through ferroelectric domain rotation.

High-performance piezoelectrics benefit transducers and sensors in a variety of electromechanical applications. The materials with the highest piezoelectric charge coefficients (d 33) are relaxor-PbTiO3 crystals, which were discovered two decades ago. We successfully grew Sm-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Sm-PMN-PT) single crystals with even higher d 33 values ranging from 3400 to 4100 picocoulombs per newton, with variation below 20% over the as-grown crystal boule, exhibiting good property uniformity. We characterized the Sm-PMN-PT on the atomic scale with scanning transmission electron microscopy and made first-principles calculations to determine that the giant piezoelectric properties arise from the enhanced local structural heterogeneity introduced by Sm3+ dopants. Rare-earth doping is thus identified as a general strategy for introducing local structural heterogeneity in order to enhance the piezoelectricity of relaxor ferroelectric crystals.

We study the aging and Mn doping effect on third generation lead based relaxor single crystals. We measured the polarization (PE) and strain with applied field on two perpendicular orientations of the rhombohedral pseudocubic [001] poled crystal. To understand these effects along the average dipoles/defect dipoles direction, we adopt a simple model with direction cosine and sine of polarization and strain. We found that when the PE measurement is perpendicular to average defect dipoles, a double loop is observed, and when it is parallel an asymmetric response is observed. We propose that the varied response found in PE measurements depend on the relative direction of average dipoles/defect dipoles to the measurement direction.

Piezoelectric materials are essential parts of the electronics and electrical equipment used for consumer and industrial applications, such as ultrasonic piezoelectric transducers, sensors, actuators, transformers, and resonators. In this review, the development of piezoelectric materials and the figures of merit for various electromechanical applications are surveyed, focusing on piezoelectric crystals, i.e., the high-performance relaxor-PbTiO3-based perovskite ferroelectric crystals and nonferroelectric high-temperature piezoelectric crystals. The uniqueness of these crystals is discussed with respect to different usages. Finally, the existing challenges and perspective for the piezoelectric crystals are discussed, with an emphasis on the temperature-dependent properties, from cryogenic temperatures up to the ultrahigh-temperature usage range.

The development of relaxor ferroelectric single crystal technology is driven by the ability to tailor ferroelectric properties through domain engineering not achievable in polycrystalline materials. In this study, three types of domain-engineered rhombohedral Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals were subjected to transverse high strain rate loading. The experimental results indicate that the domain configuration has a significant effect on the stress-induced depolarization and the associated charge released. A complete depolarization of the single-domain crystals with 3m symmetry is observed, while multidomain crystals with 4mm and mm2 symmetries retain a fraction of their initial remanent polarization. The complete depolarization of single-domain crystals is unique without transition to a non-polar phase, with a stress-induced charge density of 0.48 C/m2. This is up to three times higher than that of the multidomain crystals and PbZrxTi1−xO3 ferroelectric ceramics that are critical for ultrahigh-power transducer applications. The main offering of this work is to propose a detailed mechanism for complete stress-induced depolarization in ferroelectric crystals which does not involve an intermediate transformation to a non-polar phase.

The direct piezoelectric coefficient and permittivity of <001>C–0.26Pb(In1/2Nb1/2)O3-0.47Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 (PIN-PMN-PT) single crystals were simultaneously measured as functions of temperature and uniaxial compressive stress at various frequencies. The results show a nonlinear increase of the piezoelectric coefficient from ∼1300 pC/N at 25 °C to over 8000 pC/N at 99 °C, followed by a sharp decrease and gradual decay to zero. The peak in piezoelectric coefficient coincides with a dielectric anomaly that is associated with a rhombohedral to tetragonal phase transition. An increase of the compressive bias stress reduced the magnitude of the peak in piezoelectric coefficient and shifted it to lower temperatures, revealing an initial increase in the piezoelectric response understood to be due to a stress-induced phase transition. The large-signal macroscopic constitutive behavior was characterized at various compressive stresses from 25 °C to 150 °C. These data are contrasted with the small-signal piezoelectric measurements and show the combined influence of stress and temperature on the electromechanical properties and stress-induced phase transitions in relaxor ferroelectric PIN-PMN-PT single crystals. Implications of the results for the application window of single-crystal PIN-PMN-PT transducers are discussed.

Relaxor ferroelectric single crystals have triggered revolution in electromechanical systems due to their superior piezoelectric properties. Here the results are reported on experimental studies of energy harvested from (1-y-x)Pb(In1/2Nb1/2)O3–(y)Pb(Mg1/3Nb2/3)O3–(x)PbTiO3 (PIN-PMN-PT) crystals under high strain rate loading. Precise control of ferroelectric properties through composition, size and crystallographic orientation of domains made it possible to identify single crystals that release up to three times more electric charge density than that produced by PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5) ferroelectric ceramics under identical loading conditions. The obtained results indicate that PIN-PMN-PT crystals became completely depolarized under 3.9 GPa compression. It was found that the energy density generated in the crystals during depolarization in the high voltage mode is four times higher than that for PZT 52/48 and 95/5. The obtained results promise new single crystal applications in ultrahigh-power transducers that are capable of producing hundreds kilovolt pulses and gigawatt-peak power microwave radiation.

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric properties is in the range of 50-80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.

The electromechanical properties of [111]-oriented tetragonal Pb(In1/2Nb1/2O3)-Pb(Mg1/3Nb2/3O3)-PbTiO3 (PIN-PMN-PT) crystals were investigated for potential high frequency ultrasonic transducers. The domain-engineered tetragonal crystals exhibit an ultrahigh free dielectric permittivity ε33T > 10 000 with a moderate electromechanical coupling factor k33 ∼ 0.79, leading to a high clamped dielectric permittivity ε33S of 2800, significantly higher than those of the rhombohedral relaxor-PT crystals and high-K (dielectric permittivity) piezoelectric ceramics. Of particular significance is that the [111]-oriented tetragonal crystals were found to possess high elastic stiffness, with frequency constant N33 of ∼2400 Hz m, allowing relatively easy fabrication of high-frequency transducers. In addition, no scaling effect of piezoelectric and dielectric properties was observed down to thickness of 0.1 mm, corresponding to an operational frequency of ∼24 MHz. These advantages of [111]-oriented tetragonal PIN-PMN-PT crystals will benefit high-frequency ultrasonic array transducers, allowing for high sensitivity, broad bandwidth, and reduced noise/crosstalk.

Unique properties have been obtained by defect dipole engineering in relaxor-PT single crystals.

Relaxor-PbTiO3 (PT) based ferroelectric crystals with the perovskite structure have been investigated over the last few decades due to their ultrahigh piezoelectric coefficients (d33 > 1500 pC/N) and electromechanical coupling factors (k33 > 90%), far outperforming state-of-the-art ferroelectric polycrystalline Pb(Zr,Ti)O3 ceramics, and are at the forefront of advanced electroacoustic applications. In this review, the performance merits of relaxor-PT crystals in various electroacoustic devices are presented from a piezoelectric material viewpoint. Opportunities come from not only the ultrahigh properties, specifically coupling and piezoelectric coefficients, but through novel vibration modes and crystallographic/domain engineering. Figure of merits (FOMs) of crystals with various compositions and phases were established for various applications, including medical ultrasonic transducers, underwater transducers, acoustic sensors and tweezers. For each device application, recent developments in relaxor-PT ferroelectric crystals were surveyed and compared with state-of-the-art polycrystalline piezoelectrics, with an emphasis on their strong anisotropic features and crystallographic uniqueness, including engineered domain–property relationships. This review starts with an introduction on electroacoustic transducers and the history of piezoelectric materials. The development of the high performance relaxor-PT single crystals, with a focus on their uniqueness in transducer applications, is then discussed. In the third part, various FOMs of piezoelectric materials for a wide range of ultrasound applications, including diagnostic ultrasound, therapeutic ultrasound, underwater acoustic and passive sensors, tactile sensors, acoustic tweezers and ultrasonic motors, are evaluated to provide a thorough understanding of the materials’ behavior under operational conditions. Structure–property–performance relationships are then established. Finally, the impacts and challenges of relaxor-PT crystals are summarized to guide on-going and future research in the development of relaxor-PT crystals for the next generation electroacoustic transducers.

Compared to Pb(Zr1−xTix)O3 (PZT) polycrystalline ceramics, relaxor-PT single crystals offer significantly improved performance with extremely high electromechanical coupling and piezoelectric coefficients, making them promising materials for piezoelectric transducers, sensors and actuators. The recent advances in crystal growth and characterization of relaxor-PT-based ferroelectric single crystals are reviewed in this paper with emphases on the following topics: (1) the large crystal growth of binary and ternary relaxor-PT-based ferroelectric crystals for commercialization; (2) the composition segregation in the crystals grown from such a solid-solution system and possible solutions to reduce it; (3) the crystal growth from new binary and ternary compositions to expand the operating temperature and electric field; (4) the crystallographic orientation dependence and anisotropic behaviors of relaxor-PT-based ferroelectriccrystals; and (5) the characterization of the dielectric, elastic and piezoelectric properties of the relaxor-PT-based ferroelectriccrystals under small and large electric fields.

In this work, crystal growth and characterization of PIN–PMN–PT (29–59% PIN and 28–35% PT) were conducted to understand how PIN ratio in the PIN–PMN–PT system impacts its phase stability during crystallization. High-quality PIN–PMN–PT crystals with 36% PIN were obtained using the self-seeded Bridgman process, even though the cubic phase In2O3 formed at the very beginning of solidification. The melt became more unstable when the PIN ratio in the PIN–PMN–PT system increased to 49% and above, which affected the composition and quality of the as-grown crystals significantly. By increasing the PIN to 36% in PIN–PMN–PT crystal, the rhombohedral-to-tetragonal phase transition temperatures and the coercive field reached 115–135°C and 4.5~5.6 kV/cm, respectively, that greatly expanded the operation domains compared to PMN–PT crystals.

The hydrostatic piezoelectric properties of [011] poled Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) crystals and corresponding 2-2 crystal/epoxy composites were investigated. The crystal volume ratio and compositional dependencies of the hydrostatic charge and voltage coefficients (dh and gh ) and hydrostatic figure of merit (FOM) dh  × gh were determined, where large FOM value of 3.2 pm2/N with high stability as a function of hydrostatic pressure was achieved for rhombohedral crystal composites. In addition, the stress amplification effects of the face-plate and different epoxy matrixes were investigated, with maximum FOM value being on the order of 92 pm2/N, indicating that 2-2 crystal/epoxy composites are promising materials for hydrostatic applications.

To minimize pyroelectric effects while keeping high piezoelectric effects in relaxor-PbTiO3 single crystals, the crystallographic orientation dependence of the pyroelectric and piezoelectric coefficients were investigated for binary (1 - x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PMN-PT), ternary (1 - x - y)Pb(In1/2Nb1/2)O-3-yPb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PIN-PMN-PT) and Mn-doped PIN-PMN-PT single crystals with the "4R" multidomain state. The secondary pyroelectric coefficients were calculated from the thermodynamic inter-relationship between the piezoelectric, elastic, and thermal expansion coefficients, being on the order of (1.16-1.23) x 10(-4) C m(-2) K-1 for binary crystals and (0.97-2.03) x 10(-4) C m(-2) K-1 for ternary ones. The primary pyroelectric coefficients were -(6.73-6.84) x 10(-4) C m(-2) K-1 and -(5.44-6.43) x 10(-4) C m(-2) K-1 for binary and ternary crystals, respectively. The pyroelectric coefficients could be reduced by matrix rotation, but at the cost of decreasing longitudinal piezoelectric coefficients d(33). Of particular interest is that the maximum piezoelectric coefficients d(24)(*) at theta = +/- 55 degrees and d(34)(*) at theta = +/- 35 degrees by a counterclockwise rotation of theta about the X axis (theta is the rotation angle about the coordinate axes), or d(15)(*) at theta = +/- 55 degrees, and d(35)(*) at theta = +/- 35 degrees by a counterclockwise rotation the Y axis, were found on the order of 3000 pC N-1. The corresponding pyroelectric coefficients could be reduced by similar to 20%. The reduced pyroelectric coefficients that can contribute to decrease undesirable output signals, together with the high piezoelectric coefficients, enable relaxor-PT crystals as favorable candidates for high-sensitivity piezoelectric sensors. (C) 2014 Elsevier B.V. All rights reserved.