Relaxor Ferroelectric Single Crystals Research Articles

Mesophase induced by alternating-current poling in relaxor ferroelectric single crystals

Alternating-current poling (AC-Poling) has attracted wide interests in enhancing piezoelectric performance of ferroelectric single crystals. However, the mechanism of phase transformations and domain morphology underlying AC-Poling has not been thoroughly investigated. In this work, we have systematically studied the AC-poling effect on domain structures and piezoelectric properties in the relaxor ferroelectric single crystals of 0.24Pb(In1/2Nb1/2)O3–0.44Pb(Mg1/3Nb2/3)O3–0.32PbTiO3. It is shown that the piezoelectric constant (d33) and permittivity (ε33) are greatly enhanced via [001]-AC-poling compared to DC-poling, related to the presence of modified domain configurations as indicated previously. For [110]-oriented specimens, the piezoelectricity through AC-poling is only half as that for the DC-poled single crystals. We attribute this to the transition from the monoclinic-B phase to an orthorhombic phase under AC-poling, confirmed by synchrotron radiation X-ray diffraction and piezo-response force microscopy. The transition to the orthorhombic phase is likely a consequence of lower Gibbs energy. This study on orientation-dependent characteristics of AC-poling for PIN-PMN-PT single crystals will guide the development of AC-poling technology in applications.

Piezoelectricity and up-conversion photoluminescence of Er3+-doped Pb(Zn1/3Nb2/3)O3- PbTiO3 single crystals

Pure Pb(Zn1/3Nb2/3)O3-11mol%PbTiO3 (PZN-11PT) and Er3+-doped Pb(Zn1/3Nb2/3)O3-11 mol%PbTiO3 (PZN-11PT-Er) relaxor ferroelectric single crystals were grown by large gradient high-temperature flux method. The phase structure, electrical properties, and up-conversion photoluminescence (UC PL) of the single crystal were studied systematically. The results show that PZN-11PT-Er has a pure perovskite structure with the coexistence of rhombohedral and tetragonal phases. The piezoelectric coefficient (d33) with the Er3+ dope increases to 1550 pC/N from 854 pC/N than without dopant. However, the coercive electric field (EC) is maintained constant in spite that the remnant polarization (Pr) is increased from 25 μC/cm2 to 51 μC/cm2. The dielectric relaxation behavior of PZN-11PT was absolutely enhanced by rare Er3+-doped. In addition, UC PL was successfully achieved for PZN-11PT-Er. Optical temperature sensing property of PZN-11PT-Er was studied based on the fluorescence intensity ratio technique, showing its potential for use in a wide temperature region. These results indicate that the PZN-11PT-Er relaxor ferroelectric single crystals are suitable for applications in electromechanical coupling devices and optical temperature sensing, simultaneously.

Huge piezoelectricity and electro-optic effects in rhombohedral relaxor ferroelectric single crystals by Sm3+ doping

In recent years, relaxor ferroelectric single crystals have attracted people's attention and research because of their excellent piezoelectric properties at morphotropic phase boundary(MPB). The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) crystals have higher Curie temperature and coercive field, which have the opportunity to be applied in high-temperature devices. The crystals of the rhombohedral phase have better stability, but their performance is not as good as that of the MPB component crystals. In this paper, the piezoelectric properties of rhombohedral PIN-PMN-28PT single crystals are improved by Sm3+ doping. The piezoelectric coefficient d33 after AC polarization along [001] direction can reach 3125pC/N, which is 60% higher than that of undoped crystals. Meanwhile, the crystal exhibits excellent optical performance after DC polarization along [110] direction. The crystal has an effective electro-optic coefficient of 386 pm/V at room temperature and a stable frequency-dependent characteristic, which is expected to be an ideal material for electro-optic devices.

Research on low-frequency bender disk transducer driven by multiple relaxor ferroelectric single crystal disks

In this paper, we investigate the low-frequency bender disk transducer designed by the relaxor ferroelectric single crystal. First, we introduce the principle of the bender disk transducer, and use multiple single crystal disks as driving materials to excite the bending vibration mode of the metal plate, which reduces the operating frequency of the transducer. Then we establish the three-dimensional finite element model of the bender disk transducer driven by multiple single crystal disks, analyze the influence of the number and position distribution of single crystal disks on the transducer performance, and compare with that of the piezoelectric ceramic transducer with the same structure. Finally, we manufacture the proposed relaxor ferroelectric single crystal, piezoelectric ceramic transducers and the conventional piezoelectric ceramic bender disk transducer respectively, and carry out the experimental measurement in an anechoic water tank. The experimental results show that for the proposed single crystal transducer, its measured maximum transmitting voltage response (TVR) is 126.2 dB at 1.1 kHz, which is 13.4 dB higher than that of the proposed piezoelectric ceramic transducer, and its frequency corresponding to the maximum TVR is reduced by 700 Hz compared with the conventional piezoelectric ceramic bender disk transducer.

Thermal expansion properties of three-dimensional relaxor ferroelectric single crystals

Large-size Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals have been successfully produced. Nevertheless, the susceptibility of these crystals to cracking substantially hampers their application. This study investigates the thermal expansion characteristics of PMN-PT and PIN-PMN-PT crystals oriented along the 〈100〉, 〈110〉, and 〈111〉 directions, revealing no significant anisotropy. The average thermal expansion coefficients for the PMN-PT and PIN-PMN-PT crystals range from 7.77 to 8.21 × 10−6 K−1 and from 6.59 to 6.79 × 10−6 K−1, respectively, within the temperature range of 20 to 600 °C. Interestingly, the PMN-PT and PIN-PMN-PT crystals demonstrate unusual thermal expansion behavior around the phase transition temperature. The magnitudes of their thermal expansion coefficients are comparable to those of certain commercial crystals but are lower than that of platinum. The main causes inferred for crystal cracking include the pressure exerted by the platinum crucible and the abnormal thermal expansion behavior around the phase transition temperature.

Growth of large-sized relaxor ferroelectric PZN-PT single crystals by modified flux growth method

A novel bottom-cooling high-temperature solution growth technique is developed for growing large-sized relaxor ferroelectric 0.91Pb(Zn1/3Nb2/3O3)-0.09PbTiO3 (PZN-PT) single crystals. During the growth, an inverse temperature gradient is maintained in the crucible base by flowing air at a controlled rate. This method restricts the number of spontaneously nucleated crystals at crucible bottom, reduces loss of volatile PbO component and favours the growth of large-sized PZN-PT single crystals. Large-sized PZN-PT single crystals of dimensions ∼ 22 × 20 × 14 mm3 are reproducibly grown by the proposed method. The electrical characteristics of the PZN-PT wafers oriented along the 〈100〉, 〈010〉 and 〈001〉 directions are investigated. PZN-PT wafers oriented along the 〈001〉 direction exhibited superior piezoelectric coefficient (d33) of ∼ 2221 pm/V. The homogeneity of the physical parameters is analysed by preparing 10 elements with dimensions of ∼ 5 × 2.5 × 2.5 mm3 which were cut from single wafer oriented along the 〈001〉 direction. The ferro-, piezo- and dielectric characteristics of these wafers were found to be highly uniform with small standard deviation. The observation of d33 value with less than 2 % deviation from mean value confirms the growth of highly quality PZN-PT single crystals.

Mechanically induced reversible/irreversible phase transition in PMN–0.3PT single crystal: A phase-field simulation

Relaxor ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) have outstanding electromechanical properties in the linear regime. When operated across a phase transition, these properties are significantly enhanced. Understanding the phase transition mechanism under electromechanical external fields is crucial for the new application of PMN–PT that takes advantage of this phase transition. In the present study, the phase transition of PMN–0.3PT single crystals subjected to a mechanical loading/unloading process and the effects of electric field on the phase transition and electromechanical responses of PMN–0.3PT single crystal under coupled mechanical-electrical loading were systematically investigated using a thermodynamics-based phase-field model. The roles the different energy terms play in the evolution of domain and phase structures were assessed. These findings have important implications for both understanding of the phase transition of relaxor ferroelectric single crystal PMN–0.3PT and applications that take advantage of phase transitions in these materials. The model results for the reversible/irreversible phase transition of PMN–0.3PT during the mechanical loading/unloading process are qualitatively consistent with experimental results.

A single crystal Lamb wave sensing array

This paper reports on a multi-element relaxor ferroelectric single crystal (RFSC) based acoustic emission (AE) sensor called LAMDA (linear array for modal decomposition and analysis). This sensor is being developed foracoustic-signature detection applications, including for AE-based damage detection on space-based and undersea platforms. RFSC [011] Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (or PIN-PMN-PT) was machined into 200 μm thick × 1 mm long × 4 mm wide elements, with 16 of these elements arranged on a flexible-polyimide-carrier to form a LAMDA. This sensor was bonded to a 1.6 mm thick aluminium plate with dimensions 600 mm x 600 mm. Acoustic emissions consisting of Lamb waves (e.g., A0, S0) were generated in the plate using both piezoceramic (Pz26) disk-actuators and pencil lead breaks (PLBs). LAMDA measurements and one-dimensional laser-vibrometry were undertaken on the plate and compared with two-dimensional multi-physics model predictions. The plane-strain model geometry comprised a rectangular-section 1.6 mm thick and 600 mm long with a LAMDA located centrally. An AE, being a 5.5-cycle Hann-windowed function with centre-frequencies 300–1000 kHz, was introduced 150 mm from the LAMDA via point loading perpendicular to the surface. The Lamb wave dispersion-curves generated from the model showed good agreement with the experimental curves determined from LAMDA and laser-vibrometry.

Enhanced piezoelectric and optical properties of tetragonal Sm‐doped Pb(In1/2Nb1/2)–Pb(Mg1/3Nb2/3)–PbTiO3 crystals

AbstractRelaxor ferroelectric single crystal Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) has received extensive research and attention due to its excellent piezoelectric, electromechanical, and other properties. In particular, tetragonal relaxor ferroelectric single crystals have shown greater application potential in high‐temperature devices due to their higher Curie temperature and better stability. However, the low piezoelectric performance of tetragonal crystals also greatly limits its application, and research on its optical properties is not sufficient. In this paper, the tetragonal phase Sm–PIN–PMN–PT single crystal was obtained by the Bridgman method, and its piezoelectric and electro‐optical properties are studied. At the same time, we gave a complete set of piezoelectric, dielectric, and elastic coefficient matrices. The results show that the crystal has excellent piezoelectric and electromechanical properties. The piezoelectric coefficient can reach 905pC/N, the electromechanical coupling coefficient k33 is 85%, and the kt is 72%. The transmittance of the sample polarized along [001] direction can reach 66%. The effective electro‐optical coefficient γc is 60 pm/V at room temperature and can reach 86 pm/V at 70°C. It has a wide operating temperature range and stable performance with frequency variation, which has certain reference significance for application in new electro‐optical devices.

Time-resolved nanobeam X-ray diffraction of a relaxor ferroelectric single crystal under an alternating electric field

Time-resolved nanobeam X-ray diffraction of a relaxor ferroelectric single crystal under an alternating electric field

Orientation effects, hydrostatic response, and figures of merit in 2–2-type composites based on relaxor-ferroelectric single crystals

The article reports new results on the hydrostatic performance of laminar piezo-active composites based on domain-engineered relaxor-ferroelectric single crystals (SCs) with the perovskite-type structure. Layers of the composites are either single-crystal poled along [011] (where rotations of the main crystallographic axes around two co-ordinate axes are considered) or porous polymer, with aligned spheroidal pores. These composites are described by 2–2–0 connectivity. An influence of the rotation of the main crystallographic axes and porosity is analyzed, and maxima of the hydrostatic piezoelectric coefficient figure of merit and electromechanical coupling factor of the composites are found as functions of a few parameters. New diagrams are built to show regions of the large (over 1000 pC/N) at variations of two rotation angles in the single-crystal layers. Large values of the hydrostatic figure of merit ∼ (10−10 – 10−9) Pa−1 and electromechanical coupling factor are achieved in specific volume-fraction and rotation-angle ranges. These and other large values of the hydrostatic parameters of the studied 2–2-type composites are important for effective hydroacoustic applications.

Fabrication of titanium in-diffusion waveguide in the PIN-PMN-PT single crystal

Fabrication of the optical waveguide is essential for the application of high-performance relaxor ferroelectric single crystals in broadband integrated electro-optic devices. Here, a multimode titanium in-diffusion planar waveguide is demonstrated in a rhombohedral phase Pb(In1/2Nb2/3)O3–Pb(In1/2Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystal. Influences of titanium in-diffusion on the crystalline phase and composition were carefully studied. Guided modes in the planar waveguide were characterized by prism couple measurements. Using the inverse Wentzel-Krames-Brillouin method, the refractive index profile in the waveguide was constructed. The results show that the PIN-PMN-PT crystal retains its single crystal structure and excellent electro-optic response after titanium in-diffusion. The mode refractive index change between the diffused layer and substrate crystal is approximately 3%, which is sufficient to constrain the energy of transmitted light. Moreover, the titanium-diffused PIN-PMN-PT waveguide is confirmed to be a graded optical waveguide with a Gaussian index profile. Our work indicates that the titanium in-diffusion is a feasible way to fabricate waveguides in PIN-PMN-PT crystals, which is of great significance for their application in integrated photonic devices.

Pure- and Pseudo-Lateral-Field-Excitation Characteristics of Relaxor Ferroelectric Single Crystal PMN-PT.

The relaxor ferroelectric single crystal (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) has high piezoelectric constants, and thus has a good application prospect in the field of highly sensitive piezoelectric sensors. In this paper, for relaxor ferroelectric single crystal PMN-PT, the bulk acoustic wave characteristics on pure- and pseudo-lateral-field-excitation (pure- and pseudo-LFE) modes are investigated. LFE piezoelectric coupling coefficients and acoustic wave phase velocities for PMN-PT crystals in different cuts and electric field directions are calculated. On this basis, the optimal cuts of pure-LFE and pseudo-LFE modes of relaxor ferroelectric single crystal PMN-PT are obtained, namely, (zxt)45° and (zxtl)90°/90°, respectively. Finally, finite element simulations are carried out to verify the cuts of pure-LFE and pseudo-LFE modes. The simulation results show that the PMN-PT acoustic wave devices in pure-LFE mode have good energy-trapping effects. For PMN-PT acoustic wave devices in pseudo-LFE mode, when the device is in air, no obvious energy-trapping emerges; when the water (as a virtual electrode) is added to the surface of the crystal plate, an obvious resonance peak and the energy-trapping effect appears. Therefore, the PMN-PT pure-LFE device is suitable for gas-phase detections. While the PMN-PT pseudo-LFE device is suitable for liquid-phase detections. The above results verify the correctness of the cuts of the two modes. The research results provide an important basis for the development of highly sensitive LFE piezoelectric sensors based on relaxor ferroelectric single crystal PMN-PT.

Giant piezoelectric response in Ho-doped PbMg1/3Nb2/3TiO3 relaxor ferroelectric single crystals via in-situ neutron scattering

The complex chemical and structural heterogeneity of relaxor ferroelectrics has made the origins of the giant piezoresponse extremely difficult to understand. Here, we successfully grew Ho-doped Pb(Mg1/3Nb2/3)O3–PbTiO3 (Ho-PMNT) single crystals with even higher d33, S33 and dielectric constant ε33/ε0 values of 3900 pC N−1, 0.34% and 15,000. We employed the in situ neutron diffraction to identify that the giant piezoelectric response of the Ho-PMNT originates from the composition near the tricritical triple point of a cubic paraelectric phase (C), ferroelectric monoclinic (M), and tetragonal (T) phases. It leads to a nearly polarization isotropy and thus facilitates polarization rotation between different ferroelectric states. The results of the neutron pair distribution function combined with aberration-corrected scanning transmission electron microscopy qualitatively analyze the angstrom-nanoscaled heterogeneities and their connection to local polarization. The Pb2+ displacement direction of <110> is connected to the A site ordered polarization. There were also observed the different separation distances between the B-site atoms and the neighboring O atoms. It identifies the giant piezoelectric properties arise that the Ho-dopant immensely disrupt long-range polarization and enhance the local structural heterogeneity in the tricritical triple point.

The first 2D organic-inorganic hybrid relaxor-ferroelectric single crystal

The first 2D organic-inorganic hybrid relaxor-ferroelectric single crystal

Research and Experimental Verification of a Flextensional Disk Transducer Based on Relaxor Ferroelectric Single Crystals

In this article, the electroacoustic properties of the flextensional disk transducer based on relaxor ferroelectric single crystals are studied. First, the transducer structure, consisting of relaxor ferroelectric single crystals, metal plates, and air cavity, and an operating principle are introduced. Then, we investigate, by finite element modeling, the influence of different air cavity sizes on the transducer behavior. Furthermore, we optimize the size of the air cavity and analyze the performance of flextensional disk transducers based on relaxor ferroelectric single crystals and piezoelectric ceramics, such as the resonant frequency and transmitting voltage response (TVR). Finally, transducers of the same size are manufactured using the two kinds of materials, and the experimental measurements are carried out in an anechoic water tank. The measured maximum TVR of the single-crystal transducer is 141.04 dB at 22.2 kHz. Compared with the piezoelectric ceramic transducer, the maximum TVR of the single-crystal transducer is increased by 12.51 dB, and the corresponding resonant frequency is reduced by 4.8 kHz, which extends the working frequency.

Enhanced piezoelectric properties and domain morphology under alternating current electric field poled in [001]-oriented PIN-PMN-PT single crystal

The piezoelectric and dielectric properties of PMN-PT single crystals were significantly enhanced by alternating current electric field poling (ACP). In this work, to investigate the mechanisms of piezoelectric performance enhancement in relaxor ferroelectric single crystals by ACP, a [001]-oriented PIN-PMN-PT single crystal with a diameter of 3 in was grown by the modified Bridgman method, and a series of single crystal samples within 100 mm of the height of the crystal boule were prepared. Compared with their direct current electric field poling (DCP) counterparts, the electrical properties of single crystal samples at different heights by ACP were regularly enhanced. The piezoelectric coefficient d33 and the dielectric constant ɛ33 of the rhombohedral samples both increased by nearly 20%. Based on the results of polarized light microscopy, the domain wall in [001]-poled ACP samples could not be observed along the [001] direction. The brightness of polarized light propagating along the [010] orientation was enhanced after ACP. The domain images of {100} in the DCP and ACP samples were observed by piezoelectric force microscopy. The results showed that the domain size of ACP samples increased. The existence of layered domains can be clearly found in the scanning electron microscopy results of the stress fracture surface of the ACP sample. According to the analysis, the improvement of the piezoelectric performance in ACP samples comes from the elimination of the 71° domain walls. This work demonstrates that certain ACPs can regulate the domain structure and steadily improve the piezoelectric properties of R-phase PIN-PMN-PT single crystals.

Boosting the piezoelectric property of relaxor ferroelectric single crystal via active manipulation of defect dipole polarization

To further enhance the property of piezoelectric materials is of great significance to improve the overall performance of electro-mechanical devices. Here in this work, we propose a thermal annealing and high temperature poling approach to achieve significantly enhanced piezoelectricity in Pb(In1/2Nb1/2)O3Pb(Mg1/3Nb2/3)O3PbTiO3 (PIN-PMN-PT) crystals with a morphotropic phase boundary (MPB) composition. The main idea of our approach is to realize a more sufficiently polarized crystal via active manipulation of defects and orientation of defect polarization. Manipulation of defect dipoles by the high temperature poling is proved by the piezo-response force microscopy. Finally, a d33 of 3 300 pC/N and a SE of 0.25% are obtained, nearly 60% higher than that of conventionally poled crystals. Moreover, such a boosting of piezoelectric property is obtained under a maintained Curie temperature. Our research not only reveals the active control of defect dipole via modified poling method in the PIN-PMN-PT crystal, but also provides a feasible strategy to further improve the property of piezoelectric materials.

Ultrahigh focal sensitivity in a relaxor ferroelectric crystal-based piezoelectric adaptive lens

Traditional piezoelectric adaptive lenses (ALENS) are fabricated by piezoceramics with transparent liquids as the filling media. However, it is challenging to achieve high focal sensitivity and long-time robustness because of the low piezoelectricity of ceramics as well as the evaporation and leakage of the liquids. To overcome the above-mentioned issues, we design a piezoelectric lens based on a radial extension-arching mode by using polydimethylsiloxane films and Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) relaxor ferroelectric single crystals to replace the transparent liquids and Pb(Zr, Ti)O3 (PZT) ceramics, respectively. Due to the ultrahigh piezoelectric properties (d33 ∼ 1500 pC N−1 and d31 ∼ 730 pC N−1) of the PIMNT crystals and the optimized radial extension-arching structure, an ultrahigh focal sensitivity (8.5 cm V−1 and a fast response time (∼102 μs) is achieved, outperforming conventional ALENS based on piezoceramic actuators (∼103 μs and ∼10−1 cm V−1) and dielectric elastomer actuators (∼105 μs and ∼10−2 cm V−1). The largest output displacement of our designed ALENS is up to 53.6 μm at 4.2 kHz under 80 Vpp, and its focus is in the range of 57.44 cm to ∞. Furthermore, its performance remains unchanged after 4 × 107 vibration cycles, indicating its long-time robustness. This work sheds light on the design of advanced adaptive optical systems, where an ultrahigh focal sensitivity and a fast response are required.

Exploration of the mechanisms enabling high performance in relaxor ferroelectric crystals

<p indent="0mm">Relaxor ferroelectric single crystals, exhibiting excellent dielectric, piezoelectric, electro-optic, and pyroelectric properties, are important functional dielectric materials in electronic technology. Since the 1990s, relaxor ferroelectric crystals have attracted considerable attention in the ferroelectric and piezoelectric research fields and improved the performance of numerous piezoelectric devices, especially medical ultrasonic imaging transducers. In this paper, we briefly introduce the history of relaxor ferroelectric crystals and then focus on the research progress of our group in recent years, as listed below. (1) To elucidate the contribution of polar nanoregions (PNRs)<italic> </italic>to piezoelectricity, we performed closely integrated experimental and computational studies on relaxor ferroelectric crystals. In this work, we obtained key experimental evidence (low-temperature dielectric relaxation) for the contribution of PNRs to the piezoelectric activity in relaxor-PbTiO₃ (PT) crystals via cryogenic measurements, and more importantly, for the first time, we quantified the contribution of PNRs accounting for 50%–80% of the room-temperature dielectric and piezoelectric properties. Based on the phase-field simulations, we proposed a mesoscale mechanism wherein the PNRs are aligned in a ferroelectric matrix facilitating the polarization rotation, which successfully explains the contribution of PNRs to dielectric/piezoelectric properties. This work opens up a new material design paradigm that introduces local heterogeneities to achieve enhanced macroscopic responses. (2) Based on the origin of high piezoelectric activity in relaxor ferroelectric crystals, we proposed a theoretical approach, i.e., judiciously introducing local structure heterogeneity, to engineer the interfacial energies, thereby increasing the piezoelectricity of ferroelectric materials. According to this method, we designed and fabricated a series of rare earth element-doped relaxor ferroelectric crystals with piezoelectric coefficients <italic>d</italic>₃₃ in the 3400–4100 pC/N, double the values of the undoped counterparts. The newly developed piezoelectric materials offer potential benefits for piezoelectric devices, especially high-frequency medical transducers, where ultrahigh clamped dielectric constant (~3000) improves the electrical impedance matching of the transducers, thereby increasing the sensitivity and decreasing the insertion loss in the ultracompact transducers. (3) Using phase-field simulations and experimental measurements, we transformed the originally opaque [001]-poled rhombohedral PMN-PT crystals into a transparent one by using an AC electric field to engineer the domain structure. These crystals possess ultrahigh piezoelectric coefficient <italic>d</italic>₃₃ (&gt;2100 pC/N), outstanding electromechanical coupling factor <italic>k</italic>₃₃ (~94%), and large electro-optical coefficient <italic>γ</italic>₃₃<sc>(~220 pm/V),</sc> far beyond the performance of the state-of-the-art transparent ferroelectric crystal LiNbO₃, showing great potential in various hybrid device applications, including photoacoustic medical transducers and self-energy-harvesting touchscreens. Furthermore, we discovered that the larger domain sizes lead to higher piezoelectricity in [001]-poled rhombohedral perovskite ferroelectric crystals, opposing the long-standing belief that a smaller domain size always results in higher piezoelectricity in ferroelectric crystals. This observation may benefit the future design of piezoelectric materials. Finally, the applications of our newly designed relaxor ferroelectric crystals in electromechanical and electro-optical devices are introduced, and the future perspectives of relaxor ferroelectric crystals are discussed.