Relaxor-based Ferroelectric Single Crystals Research Articles

Multi-type nanoscale domain switching dynamics in tetragonal PIN-PMN-PT single crystal under electrical bias

Domain switching coupled with polarization reorientation allows ferroelectrics to exhibit high potential for use in nonvolatile memories, electro-optic devices, and nanoelectronics. Although several studies have elucidated domain switching, the research on switching dynamics of complex nanoscale domain structures in relaxor-based ferroelectric materials has been lacking. Herein, the domain structure and domain switching dynamics in tetragonal PIMN-PT single crystals were systemically studied via piezoresponse force microscopy. An interlocking multi-type domain pattern comprising irregular 180° ferroelectric domains and regular 90° ferroelastic domains was observed and its formation mechanism was explored. Different domain switching dynamics of field-dependent responses were investigated. The results indicate that T-phase PIMN-PT single crystals exhibit a hierarchical domain switching process. Under a low electrical-bias stimuli (<10 V), the nucleation and growth of 180° domains dominate the switching process. By increasing the electrical bias from 10 V to 80 V, 90° domain switching was gradually completed and the sample achieved a single-domain state. The nucleation and growth mechanism of ferroelectric domains under electrical-bias stimuli were also discussed. Overall, our results deepened the understanding of ferroelectric switching in complex nanoscale domain structures and facilitate the use of precise domain tailoring technology for fabricating T-phase relaxor-based ferroelectric single crystals.

Bridgman Growth and Photoelectronic Property of Relaxor-Based Ferroelectric Single Crystal Pb(Sm1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3

A relaxor-based ferroelectric single crystal with the nominal composition of xPb(Sm0.5Nb0.5)O3-(0.7‒x) Pb(Mg1/3Nb1/3)O3-0.3PbTiO3 (x = 0.01, 0.02, and 0.03) was grown by the vertical Bridgman process. The electrical properties and the ferroelectric domains, as well as the luminescent characteristics of the single crystals, were investigated systematically. The piezoelectric coefficient d33 of the single crystals are slightly higher than that of the undoped PMN-PT single crystal under direct current polarization, while the crystal wafers gain a much higher d33 value upon being polarized with alternating current voltage. The single crystals possess a decreased phase transition temperature of around 60 °C and a decreased Curie temperature of 92~116 °C compared with the undoped PMN-PT single crystal. The crystal wafers polarized with alternating current voltage exhibited a desirable optical transmittance, which is associated with the domain structure changes inside the crystal medium. The domain density of the crystal wafers under alternating current polarization was significantly decreased compared with the direct current polarized crystal wafers. The luminescent spectra of the crystal wafers exhibit the typical emission peaks corresponding to the characteristic transition of Sm3+ ions in the crystal lattice.

Temperature dependence of the transverse piezoelectric properties in the [001]-poled 0.25Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystal with alternating current treatment

In this work, the transverse piezoelectric properties of the pre-direct current poled (DCP) 0.25Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (0.25PIN-0.42PMN-0.33PT) single crystals were enhanced by the alternating current treatment (ACT) of 10 kVp/cm (5.8 kVrms/cm), 50 Hz, and 20 cycles. The transverse piezoelectric constant d31 of −1560 pC/N and electromechanical coupling coefficient k31 of 0.92 at room temperature were achieved in the DCP-ACT crystal, which were, respectively, 80% and 11% higher than those of the DCP crystal (d31=−870pC/N,k31=0.83) . Meanwhile, the elastic compliance constant S11E and dielectric permittivity ε33T/ε0 of the DCP-ACT crystal were, respectively, 78% and 46% higher than those of the DCP crystal. Based on the temperature dependence of dielectric properties and resonance curves, the d31, ε33T/ε0, and S11E of the DCP-ACT crystal were higher than those of the DCP crystal in the R phase region. The DCP-ACT crystal also showed a higher TFerro (110 °C) than the DCP crystal (96 °C), which was related to the intermediate phase induced by ACT. The d31 at Tferro of the DCP-ACT crystal can be −3810 pC/N, which was 2.3 times that of the DCP crystal (−1680 pC/N). In the T phase region, the DCP-ACT crystal presented a high ε33T/ε0 and attenuated impedance resonance. Moreover, ACT also affected the ferroelectric to paraelectric phase transition. This could be related to the nanoscale heterogeneous polar region induced by ACT, which enhanced the inhomogeneous state in the relaxor-based ferroelectric single crystal. ACT is a potential way for improving the transverse piezoelectric properties of the PIN-PMN-PT single crystal.

Phase stability and Landau phenomenological model of relaxor ferroelectric single crystals 0.78Pb(Mg1/3Nb2/3)O3-0.22PbTiO3

Relaxor-based ferroelectric single crystal with lower PbTiO3 content has complex phase transitions and mixed ferroelectric and relaxor characteristics, making it very challenging for the construction of Landau free energy expansion crucially used for theoretical investigation of this system. In this work, relaxor behavior in 0.78Pb(Mg1/3Nb2/3)O3-0.22PbTiO3 (PMN-0.22PT) single crystals was well suppressed through careful experimental design, leaving preserved single domain state for the Landau parameter extraction in this rhombohedral-phase composition. Using these extracted Landau free energy expansion parameters, energy profile and phase coexistence were theoretically studied and compared with those of PMN-0.30PT and PMN-0.36PT single crystals. Results show that rhombohedral phase dominates in PMN-0.22PT, and tetragonal phase dominates in PMN-0.36PT around room temperature. While, rhombohedral phase and tetragonal phase coexist in MPB composition PMN-0.30PT with small discrepancy of both free energies and polarization vectors.

Investigation of High-Power Properties of PIN-PMN-PT Relaxor-Based Ferroelectric Single Crystals and PZT-4 Piezoelectric Ceramics.

We developed a high-power piezoelectric characterization system that was used to study the high-field properties of (1-x-y)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3) O3-xPbTiO3 (PIN-PMN-PT) relaxor ferroelectric single crystals and PZT-4 piezoelectric ceramics. The impedance spectrum of 31 modes was measured under constant voltage by the high-power piezoelectric system. From measuring the resonance and antiresonance frequencies, the high-field behaviors of the electromechanical coupling coefficients, elastic compliances, and piezoelectric coefficients of the PIN-PMN-PT crystals were determined and compared with commercial PZT ceramics. By fitting the equivalent circuit parameters under large electric fields, the mechanical quality factors of the PIN-PMN-PT single crystals and PZT-4 ceramics were calculated as well. The results showed that the mechanical quality factor of the PZT-4 is higher than that of PIN-PMN-PT, and the mechanical quality factors of the PZT-4 and PIN-PMN-PT both decrease sharply first and then decrease slowly with increasing the electric field. The tensile strengths of PIN-PMN-PT crystals and PZT-4 ceramics were also determined by the impedance method, where we found that the tensile strengths of PIN-PMN-PT crystal and PZT-4 ceramic were 19.6 and 76.4 MPa, respectively. The 31-mode vibrators of PIN-PMN-PT crystals and PZT-4 ceramics can be driven by the largest electric field of 33 and 65 V/mm under resonance frequency, respectively.

Hydrogenated graphene oxide (H-G-SiO2) Janus structure: experimental and computational study of strong piezo-electricity response

We have investigated the piezoelectric response of the hydrogenated graphene oxide (H-G-SiO2) stacks both experimentally and theoretically. The piezoresponse force microscopy method and density-functional theory (DFT) calculations were used to study the piezoresponse effect of this structure from both experimental and computational point of views. A mono-layer graphene, made by chemical vapour deposition method, is deposited on Si/SiO2 substrate and its surface is then functionalized with hydrogen atoms. The vertical piezoresponse, observed by piezoresponse force microscopy, is measured to be about 2146 pC N−1, that is comparable to the reported state of the art piezoelectric materials such as relaxor-based ferroelectric single crystals. In order to carry out the DFT modelling, a H-Graphene-O Janus structure has been adopted, where graphene is modified by oxygen atoms adsorbed on one side while hydrogen atoms are placed on the other side. Through modelling by DFT calculations, it is revealed that, by applying out-of-plane compressive uniaxial strain, the structure preforms different piezoelectric behaviours, up to three orders of magnitude alteration by the applied strain. The demonstrated approach for enhancing the piezo-response of graphene paves the way for realizing graphene-based nanoscale sensors, actuators and transducers.

Depolarization field in relaxor-based ferroelectric single crystals under one-cycle bipolar pulse drive**Project supported by the National Natural Science Foundation of China (Grant No. 11674270), the Fundamental Research Funds for Xiamen University, China (Grant No. 20720180113), the Education and Scientific Research Project for Young and Middle-aged Teachers of Fujian Province, China (Grant No. JAT170036), the Opening Fund of Acoustics Science and

The [001]c-polarized (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN−PT) single crystals are widely used in ultrasonic detection transducers and underwater acoustic sensors. However, the relatively small coercive field (∼ 2 kV/cm) of such crystals restricts their application at high frequencies because the driving field will exceed the coercive field. The depolarization field can be considerably larger in an antiparallel direction than in a parallel direction with respect to polarization when the bipolar driving cycle starts. Thus, if the direction of the sine wave signal in the first half cycle is opposite to the polarization direction, then the depolarized domains can be repolarized in the second half of the sine cycle. However, if the direction of the sine wave signal in the first half of the cycle is along the polarization direction, then the change is negligible, and the domains switched in the second half of the sine cycle cannot be recovered. The design of electric driving method needs to allow the use of a large applied field to emit strong enough signals and produce good images. This phenomenon combined with the coercive field increases with the driving frequency, thereby making the PMN−PT single crystals usable for high-frequency applications. As such, the applied field can be considerably larger than the conventionally defined coercive field.

Temperature-dependent phase transition in [001]-oriented 0.72Pb(MgNb)O-0.28PbTiO single crystals

Abstract Temperature-dependent dielectricity and polarization of [001]C-oriented 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 relaxor-based ferroelectric single crystals were studied by using a combined method of the X-ray diffraction, dielectric spectrum, polarization-electric (P-E) field hysteresis loops, and the Landau-phenomenological theory. Results show that the room-temperature rhombohedral phase experiences a rhombohedral-monoclinic-tetragonal coexisting state, then transforms to tetragonal phase, and finally to cubic phase during the zero-field-heating process. The six-order Landau-type thermal expansion parameters for the tetragonal phase were determined by using the typical characteristics at the cubic-tetragonal phase transition in the temperature range from 91 °C to 113 °C. The calculated dielectric curve, polarizations, and P-E loops fit well with the experimental results. The phase stability and piezoelectricity are further studied and compared with those of the PMN-0.36PT single crystal. The provided methods and obtained Landau parameters can be used for further studies on the relaxor-based ferroelectric single crystals.

Long-range fluctuation of polar nanoregions in relaxor-based (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ferroelectric single crystals

The long-range fluctuations of polar nanoregions (PNRs) in relaxor-based ferroelectric single crystals (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with x = 0.29 and 0.33 were investigated by using photon correlation spectroscopy (PCS). Dual relaxation processes for the long-range fluctuation of PNRs were observed in both samples. The relaxation-times cover the range of 6–30 μs and 13–100 μs for the two relaxations which are attributed to the flipping and boundary fluctuation of PNRs, respectively. The temperature dependence of relaxation time for the slow fluctuations varies with similar trend to that for dielectric response. The flipping process of PNRs is deduced to responsible for the large dielectric response.

Integration of Oxide Semiconductor Thin Films with Relaxor-Based Ferroelectric Single Crystals with Large Reversible and Nonvolatile Modulation of Electronic Properties.

We report the fabrication of 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT)-based ferroelectric field effect transistors (FeFETs) by the epitaxial growth of cobalt-doped tin dioxide (SnO2) semiconductor thin films on PMN-0.29PT single crystals. Using such FeFETs we realized in situ, reversible, and nonvolatile manipulation of the electron carrier density and achieved a large nonvolatile modulation of the resistance (∼330%) of the SnO2:Co films through the polarization switching of PMN-0.29PT at 300 K. Particularly, combining the ferroelectric gating with piezoresponse force microscopy, X-ray diffraction, Hall effect, and magnetoresistance (MR), we rigorously disclose that both sign and magnitude of the MR are intrinsically determined by the electron carrier density, which could modify the s-d exchange interaction of the SnO2:Co films. Furthermore, we realized multilevel resistance states of the SnO2:Co films by combining the ferroelectric gating with ultraviolet light illumination, demonstrating that the FeFETs have potential applications in multistate resistive memories and electro-optical devices.

Origin of Improvement in Mechanical Quality Factor in Acceptor-Doped Relaxor-Based Ferroelectric Single Crystals

Ferroelectric materials with high mechanical quality factors ${Q}_{m}$ are used in high-power electromechanical devices, but the physical mechanism of ${Q}_{m}$ enhancement is not well understood. This study uses Rayleigh analysis to quantitatively investigate the pinning effect in acceptor-doped relaxor ferroelectric crystals. Enhancement of the longitudinal factor ${Q}_{33}$ is attributed to restricted polarization rotation, while that of the shear factor ${Q}_{15}$ is ascribed to both polarization rotation and clamped domain-wall motion. This insight into the underlying physics will guide the material optimization of device performance in $e.g.$ transducers and sensors.

Temperature and frequency dependence of the coercive field of 0.71PbMb1/3Nb2/3O3–0.29PbTiO3 relaxor-based ferroelectric single crystal

The hysteresis loop of ferroelectric materials becomes narrower with the increase in temperature due to energy barrier reduction, while the coercive field level increases with frequency due to the inertia of polarization reversal. These two competing effects determine the limiting operation field of medical imaging transducers at high frequencies. We have measured the coercive field of the 0.71PbMb1/3Nb2/3O3–0.29PbTiO3 single crystal as functions of both temperature and frequency. It was found that the coercive field linearly decreases with temperature at all frequencies. Related theoretical analysis was also performed to understand the physics behind the observed phenomena.

Relaxor-based ferroelectric single crystals grown by top-seeded solution growth method

Compared to conventional Pb(Zr1– x Ti x )O3 (PZT) polycrystalline ceramics, relaxor-based (relaxor-PT) ferroelectric single crystals have excellent performance with ultrahigh electromechanical coupling factor and piezoelectric coefficient. For example, the typical relaxor-PT ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), have electromechanical coupling factors k 33> 0.9 and piezoelectric coefficients d 33> 2000 pC/N, making them as candidate materials for the next generation of piezoelectric devices, such as piezoelectric transducers, sensors and actuators. But the difficulties for the relaxor-PT single crystals application is the preparation technique. The crystal growth technique, including high-temperature solution (flux) growth, the vertical Bridgman growth and top-seeded solution growth (TSSG) method were used for preparation of relaxor-PT single crystals. TSSG offers some advantages for growth of relaxor-PT single crystals. Therefore, in this article, recent major advances in the development of relaxor-PT single crystals are reviewed in terms of crystal growth using top-seeded solution growth method.

Phase coexistence and Landau expansion parameters for a 0.70Pb(Mg1/3Nb2/3)O3−0.30PbTiO3 single crystal

Multidomain relaxor-based ferroelectric single crystals $(1\text{\ensuremath{-}}x)\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}x\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-PT) have extraordinarily large electromechanical properties, but the origin of their giant piezoelectric properties is still not well understood. The Landau-like phenomenological theory is a feasible tool to study domain structures and their correlation with piezoelectric effects, but so far no expansion coefficients have been measured due to the phase mixture complication involved. In this work, the Landau free-energy expansion parameters for $0.70\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\text{\ensuremath{-}}0.30\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-0.30PT) single crystal were determined from the temperature-dependent polarization-electric field $(P\text{\ensuremath{-}}E)$ hysteresis loops along ${[001]}_{\mathrm{C}}$ and ${[011]}_{\mathrm{C}}$ directions, and the rhombohedral $(R)$ to tetragonal $(T)$ phase-transition temperature. Using the obtained parameters, ferroelectric and dielectric properties were quantitatively calculated and compared with experiments. Good agreement was achieved in the temperature regions of $T$ and $R$ phases, but deviations were found in the cubic-phase temperature region since the contribution of polar nanoregions was not considered. In the phase-coexistence region from 73 to $93{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, the polarization and dielectric constant can be quantitatively explained with the volume fractions of the coexisting $R$ and $T$ phases predicted by the canonical distribution. These obtained parameters can help theoretical studies and simulations of these relaxor-based ferroelectric single crystals to reveal the correlation between domain microstructures and the origin of giant electromechanical properties of multidomain PMN-PT single crystals.

Domain configuration evolution, dielectric, ferroelectric and piezoelectric properties of 0.32PIN–0.345PMN–0.335PT single crystals

Domain configuration evolution with temperature of the unpoled [001]C-oriented 0.32Pb(In1/2Nb1/2)O3–0.345Pb(Mg1/3Nb2/3)O3–0.335PbTiO3 (0.32PIN–0.345PMN–0.335PT) single crystals was studied by the polarized light microscopy (PLM). The optical observation of the domain structures reveals the coexistence of polymorphic ferroelectric phases with mainly ferroelectric monoclinic phase at room temperature and the irreversible domain evolution upon thermal cycling, which induce the high piezoelectric response in such relaxor-based ferroelectric single crystals with the morphotropic phase boundary compositions combined with polarization rotation. The temperature dependent domain evolution and dielectric behavior demonstrate the successive temperature-induced second-order ferroelectric M phase to ferroelectric tetragonal (T) phase (FEM–FET) and first-order ferroelectric T phase to paraelectric cubic (C) phase (FET–PC) ferroelectric phase transitions in the unpoled 0.32PIN–0.345PMN–0.335PT single crystals. Two dielectric loss anomalies were detected around the dielectric anomaly below 100 °C in the poled 0.32PIN–0.345PMN–0.335PT single crystals, indicating that the FEM–FET phase transition can be correlated with two different ferroelectric phase transitions, one is MA–MC, and the other is MC–T phase transition. The FEM–FET phase transition was confirmed further by the energy density measurement. The temperature dependent piezoelectric properties proved that the working temperature of the 0.32PIN–0.345PMN–0.335PT single crystals can reach 130 °C, higher around 50 °C than the Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals, indicating their promising applications in transducers used at elevated temperatures.

Local twin domains and tip-voltage-induced domain switching of monoclinicMCphase inPb(Mg1/3Nb2/3)O3−0.34PbTiO3single crystal revealed by piezoresponse force microscopy

The monoclinic (M) phases in high-performance relaxor-based ferroelectric single crystals have been recognized to be a vital structural factor for the outstanding piezoelectric property. However, due to the complexity of the structure in M phases, the understanding about it is still limited. In this paper, the local twin domains and tip-voltage-induced domain switching of the ${\mathrm{M}}_{C}$ phase in $\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}\ensuremath{-}0.34\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-0.34PT) single crystal have been intensively investigated by piezoresponse force microscopy (PFM). By theoretically analyzing the experimental patterns of domain walls on the ${(001)}_{C}$ face, the specific ${\mathrm{M}}_{C}$ twin domains in the initial annealed state of a selected area have been clarified, and the polarization orientation of the ${\mathrm{M}}_{C}$ phase in this sample is determined to be at an angle of ${29}^{\ensuremath{\circ}}$ to the ${\ensuremath{\langle}001\ensuremath{\rangle}}_{C}$ directions. In addition, based on the evolution of domains and the motion of domain walls under the step-increased PFM tip dc voltage (${V}_{\mathrm{dc}}$), the switching process and features of different types of ${\mathrm{M}}_{C}$ domain variants are visually revealed.

Determination of 60° polarization nanodomains in a relaxor-based ferroelectric single crystal

Here, we report a determination of monoclinic nanodomains in PMN-xPT with x = 31%PT by using scanning convergent beam electron diffraction (SCBED). We show the presence of 60 ± α degree nanodomains with Cm-like symmetry as well as significant variations (α) in local polarization directions across lengths of ∼10 nm. The principle of our technique is general and can be applied for the determination of polarization domains in other ferroelectric materials of different symmetry.

Fabrication of a PMN-PT single crystal-based transcranial Doppler transducer and the power regulation of its detection system.

Doppler sonographic measurement of flow velocity in the basal cerebral arteries through the intact skull was developed using a pulsed Doppler technique and 2 MHz emitting frequency. Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) were chosen to be the piezoelectric transducer material due to their ultrahigh piezoelectric coefficients, high electromechanical coupling coefficients and low dielectric loss. The pulse-echo response of the transducer was measured using the conventional pulse-echo method in a water bath at room temperature. The −6 dB bandwidth of the transducer is 68.4% and the sensitivity is −17.4 dB. In order to get a good match between transducer and detection system, different transmission powers have been regulated by changing the impedance of the transmitting electric circuit. In the middle cerebral artery (MCA) measurement photograph results, as the transmission power is increasing, the detection results become clearer and clearer. A comparison at the same transmission power for different transducers shows that the detection photograph obtained by the crystal transducer was clearer than that obtained with a commercial transducer, which should make it easier for doctors to find the cerebral arteries.

Electric-field-controlled interface strain coupling and non-volatile resistance switching of La1-xBaxMnO3 thin films epitaxially grown on relaxor-based ferroelectric single crystals

We have fabricated magnetoelectric heterostructures by growing ferromagnetic La1-xBaxMnO3 (x = 0.2, 0.4) thin films on (001)-, (110)-, and (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb1/2)O3-0.34PbTiO3 (PINT) ferroelectric single-crystal substrates. Upon poling along the [001], [110], or [111] crystal direction, the electric-field-induced non-180° domain switching gives rise to a decrease in the resistance and an enhancement of the metal-to-insulator transition temperature TC of the films. By taking advantage of the 180° ferroelectric domain switching, we identify that such changes in the resistance and TC are caused by domain switching-induced strain but not domain switching-induced accumulation or depletion of charge carriers at the interface. Further, we found that the domain switching-induced strain effects can be efficiently controlled by a magnetic field, mediated by the electronic phase separation. Moreover, we determined the evolution of the strength of the electronic phase separation against temperature and magnetic field by recording the strain-tunability of the resistance [(ΔR/R)strain] under magnetic fields. Additionally, opposing effects of domain switching-induced strain on ferromagnetism above and below 197 K for the La0.8Ba0.2MnO3 film and 150 K for the La0.6Ba0.4MnO3 film, respectively, were observed and explained by the magnetoelastic effect through adjusting the magnetic anisotropy. Finally, using the reversible ferroelastic domain switching of the PINT, we realized non-volatile resistance switching of the films at room temperature, implying potential applications of the magnetoelectric heterostructure in non-volatile memory devices.

High performance relaxor-based ferroelectric single crystals for ultrasonic transducer applications.

Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d33∼2000 pC/N, kt∼60%) near the morphotropic phase boundary (MPB). Ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals also possess outstanding performance comparable with PMN-PT single crystals, but have higher phase transition temperatures (rhombohedral to tetragonal Trt, and tetragonal to cubic Tc) and larger coercive field Ec. Therefore, these relaxor-based single crystals have been extensively employed for ultrasonic transducer applications. In this paper, an overview of our work and perspectives on using PMN-PT and PIN-PMN-PT single crystals for ultrasonic transducer applications is presented. Various types of single-element ultrasonic transducers, including endoscopic transducers, intravascular transducers, high-frequency and high-temperature transducers fabricated using the PMN-PT and PIN-PMN-PT crystals and their 2-2 and 1-3 composites are reported. Besides, the fabrication and characterization of the array transducers, such as phased array, cylindrical shaped linear array, high-temperature linear array, radial endoscopic array, and annular array, are also addressed.