Piezoelectric Single Crystals Research Articles

Poling-free relaxor-PbTiO3 single crystals

Relaxor-PbTiO3 ferroelectric single crystals have drawn attention aiming at high-end piezoelectric applications thanks to their excellent piezoelectric properties. Like all the other ferroelectrics, relaxor-PbTiO3 single crystals can only be piezoelectrically active upon being electrically poled. However, this poled state is thermally unstable, limiting their uses because of their relatively low depolarization temperature. Here, we show that a non-destructible permanent poled state can be realized in relaxor-PbTiO3 single crystals by forming a 0–3 composite in the presence of charged mobile point defects. We demonstrate this on solid-state grown 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals doped with Mn (Mn-PMNT) as a donor with well-aligned and dispersed boron-rich MgO-based inclusions (MBIs). Mn-PMNTMBI sharing [001] axis with arrayed MBIs were spontaneously polarized during cooling across the Curie temperature without an external electric field. The piezoelectric coefficient and dielectric permittivity of self-poled Mn-PMNTMBI crystals were as large as 90 % of that achieved by a direct-current poling treatment at room temperature, and such poled state was reproducible against repeated thermal cycles. We expect that the poling-free high-performance piezoelectric relaxor-PbTiO3 single crystals offer an avenue for piezoelectric-based devices by removing the working temperature limit as one of the inherent fundamental limitations.

Precise evaluation of the material constants of [011]-poled mangan-doped 0.32Pb(In1/2Nb1/2)O3-0.39Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals

Recently, there has been a surge of interest in [011]-poled Mn: PIN-PMN-PT piezoelectric single crystals for high-power transducers. These crystals boast impressive electromechanical coupling coefficients, piezoelectric constants in the transverse mode, and excellent heat resistance due to their high mechanical quality factor. To effectively design transducers using these crystals, understanding their material constants is crucial. Our study focused on determining these constants by employing the resonance method. We created eleven different resonators, analyzed their impedance spectra, and derived seventeen elastic compliance, piezoelectric, and dielectric constants. The precision of the obtained material constants was enhanced by minimizing the difference between the impedance spectra found through finite element analyses and actual measurements of each resonator. The accuracy of these derived constants was validated by comparing the impedance spectra obtained from analysis with those measured experimentally. This novel approach demonstrated a capability to derive more precise material constants than prior studies. These refined material constants hold the potential to enable more precise and effective design of acoustic transducers constructed from the single crystals.

A single crystal row–column-array for 3D ultrasound imaging

In vivo 3D ultrasound imaging with 2D-array transducers is of great importance for both clinical application and biomedical research, but it is complicated in fabrication and also very expensive in hardware due to thousands of electronic channels. In this work, we demonstrate a new fabrication process of 7-MHz 128 + 128 elements row-column-array (RCA) transducer with relaxor ferroelectric PMN-0.28PT single crystal. With piezoelectric single crystal and improved acoustic matching, the optimized performance of −6 dB bandwidth of ∼82 % and insertion loss of −44.6 dB is achieved. The axial and lateral imaging resolutions at different depth of the RCA transducer are quantified by the point spread function (PSF), and the results are respectively 0.20 mm and 0.41 mm at the depth of 7.7 mm, and 0.22 mm and 0.47 mm at the depth of 16.7 mm. The transducer is validated experimentally on a hyperechoic phantom, and 3D view and slices of B-mode images are obtained. The experimental results indicate that our developed RCA transducer can obtain high-quality 3D ultrasound images, demonstrating great potential on ultrafast 3D and functional imaging.

Shear Horizontal Guided Wave Sensors Based on CTGS Piezoelectric Crystal for High‐Temperature Structural Health Monitoring

AbstractThe development of ultrasonic‐guided wave sensors is of great significance for structural health monitoring (SHM). In this work, a shear horizontal (SH) ultrasonic guided wave sensor based on the Ca3TaGa3Si2O14 (CTGS) piezoelectric single crystal is demonstrated. The findings reveal that the CTGS‐based ultrasonic guided wave sensor is proficient in transmitting and receiving pure fundamental SH wave (SH0 wave) along two orthogonal main directions (0° and 90°) over a wide frequency range (100–350 kHz), exhibiting strong response to the SH0 wave. Under the driving voltage of 100 V, the peak‐to‐peak values of the sensor output are 110.8 and 8.0 mV at room temperature and high temperature of 600 °C, respectively. Additionally, the signal‐to‐noise ratio (SNR) of the CTGS‐based SH0 sensor is evaluated to be >18.9 dB even at the elevated temperature of 600 °C. Moreover, the CTGS‐based SH0 sensor showcases its reasonable defect localization ability at temperatures up to 600 °C, demonstrating its great potential for application in the high temperature in‐situ SHM.

Mechanically flexible piezoelectric organic single crystals for electrical energy harvesting

Mechanically flexible piezoelectric organic single crystals for electrical energy harvesting

Simulation and structural design of 2–2 PIMNT/epoxy piezoelectric composites

Piezoelectric materials are commonly used in transducers to convert electromechanical signals due to their energy conversion characteristics. We designed a PIMNT/epoxy 2–2 composite to take full advantage of the excellent beam-mode piezoelectric and acoustic features of PIMNT single crystals. Following the approach used for piezoelectric ceramic composites, we selected PIMNT piezoelectric single crystal and EPO-TEK301-2 epoxy resin for the composite, and combined finite element analysis with experimental preparation. We prepared, tested and analyzed 2–2 piezoelectric single crystal composites with varying volume fractions, which showed high electromechanical coupling properties ([Formula: see text]%) and low acoustic impedance ([Formula: see text][Formula: see text]MRayl). These encouraging findings suggest the possibility of devising high-performance ultrasonic transducers utilizing the PIMNT/epoxy 2–2 composite.

Ductile mode machining of piezoelectric single crystal by laser-assisted diamond turning process

Piezoelectric single crystals are multifunctional materials used in advanced ultrasound devices owing to their exceptional piezoelectric properties. Nevertheless, machining methods for these single crystals have been limited due to their brittle nature and material deterioration issues. Herein, we established a ductile machining process of piezoelectric single crystal based on a laser-assisted diamond turning process through comprehensive analysis. In order to achieve defect-free surfaces, we analyzed the cutting behavior of softened piezoelectric single crystals concerning crystal orientation and machining direction. The experimental studies examined the effects of processing parameters on mechanical, chemical, crystallographic, and piezoelectric properties. The cutting status was characterized by measuring acoustic emission signals and analyzing the cutting chip formation. By optimizing the process and establishing a ductile mode of diamond turning mechanisms of piezoelectric material, we machined the brittle single crystal into various shapes, such as double-sided and multi-scale microstructure, without showing any defects all over the crystal orientation. We also demonstrated the validity of the machining process for piezoelectric material through an ultrasound characteristic test, which showed that the fabricated ultrasound transducers with machined single crystal maintained ultrasonic performance without deterioration in underwater experiments.

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.

Organic-inorganic piezoelectric single-crystal TMCM-2CdCl3 with high piezoelectric properties

Organic-inorganic piezoelectric material is a kind of composite material with piezoelectricity, flexibility and plasticity. The crystals grown at room temperature can be shaped arbitrarily without polarization, and have unique advantages in shaped devices and wearable systems. In this paper, organic–inorganic piezoelectric single crystals TMCM-2CdCl3 with a perovskite molecular structure have been prepared by solution evaporation growth using trimethylammonium halide as the organic part and CdCl3 as the inorganic part. It has a monoclinic structure, and the space group is P21/n. The piezoelectric coefficient of unpolarized piezoelectric single crystals can reach 213 pC/N, making this material a competitive candidate in medical, micromechanical, and biomechanical applications.

Self‐Powered Smart Proximity‐Detection System Based on a Hybrid Magneto‐Mechano‐Electric Generator

A hybrid magneto‐mechano‐electric (H‐MME) generator that combines a Mn‐doped Pb(Mg1/3Nb2/3)O3‐Pb(Zr,Ti)O3 piezoelectric single crystal and an electromagnetic induction coil is demonstrated to convert stray magnetic noise of 60 Hz into useful electrical energy. The authors optimize the design of the piezoelectric cantilever, the weight of the magnetic mass, and the distance between the magnet and coil through theoretical simulation and experiments to maximize each contribution for the H‐MME generator. The total root mean square output power of the H‐MME generator is 28.35 mW with a power density of 0.042 mW cm−3 Oe2 in a 5 Oe magnetic field of 60 Hz, which is sufficient for driving multiple functional Internet of Things sensors that detect temperature, humidity, light, UV radiation, air pressure, and sound. In addition, a self‐powered smart proximity‐detection system (including a microcontroller unit, an ultrasonic sensor module, a piezo speaker, and a Bluetooth module) is demonstrated by rectifying the output of the H‐MME generator and controlling it using a power management circuit. The superior output power of the H‐MME generator exceeds simple sensing functions and presents the possibility of achieving battery‐free self‐powered smart devices and systems.

Relationship between crystal structure and acoustic physical properties of Ca3B(Ga,Al)3Si2O14 [B = Nb, Ta] piezoelectric single crystals

The crystal structures of Ca3Nb(Ga,Al)3Si2O14 (CNGAS) and Ca3Ta(Ga,Al)3Si2O14 (CTGAS) single crystals are investigated in this study to reveal the relationship between their crystal structures and acoustic physical properties. The positional parameters of each element for the CNGAS and CTGAS single crystals are determined with high accuracy, whereas the bond lengths and bond angles are calculated using the positional parameters. Analysis results of the crystal structures suggest that the increase of bond angles, O2-Si-O2 and Si-O2-(Ga,Al), in the O2-Si-O2-(Ga,Al) line causes the increase of their anisotropy of crystal structures. Elastic constants related to the z-axis, i.e., cE33 and cE44, increase significantly after Al substitution, which is attributed to the increase in the anisotropy of the crystal structures.

Conformally Large-Area Single-Crystal Piezocomposites with High Performance for Acoustic Transducers.

Large-area and conformal piezoelectric elements are highly desired for acoustic transducers to possess a large power source level and wide detecting range. To date, single-crystal piezocomposites attract much attention on enhancing the power source level and bandwidth for next-generation acoustic transducers, owing to their higher piezoelectric and electromechanical coupling properties compared to traditional piezocomposites. Unfortunately, it is still challenging to achieve large-area and conformal single-crystal piezocomposites because of the fragile nature, large anisotropy, and the limited grown size of piezoelectric single crystals. Here, we successfully fabricate the conformally large-area single-crystal piezocomposite with an area of 160 × 50 mm2 and a bending angle of 162° by a modified 3D-printing-assisted inserting method. The single-crystal piezocomposite exhibits a high thickness electromechanical coupling factor kt of 85% and a large piezoelectric coefficient d33 of 1150 pC/N, surpassing those of the reported large-area piezocomposites. The influence of the volume fraction and curvature radius of single-crystal PCs and acoustic transducers was investigated. Furthermore, we designed an acoustic transducer based on the conformal single-crystal piezocomposite. Benefiting from the excellent piezoelectric and electromechanical properties of the single-crystal piezocomposite, the transducer indicates a high maximum transmitting voltage response of 171.8 dB. Especially, its bandwidth (-3 dB) achieves 60 kHz with a resonant frequency of 292 kHz, which is about 1.8 times superior to the conformal acoustic transducer based on the ceramic piezocomposite with a similar resonant frequency. This work may benefit the future design and fabrication of high-performance and complex-shape piezoelectric composites as key materials for next-generation transducers.

Application of Odd Harmonic Resonances of a Single Crystal to Generation and Reception of Superharmonic Waves for Sensitive Monitoring of Heat-Treated Materials.

In nonlinear ultrasonic testing, the quadratic and more recently cubic nonlinearity parameters are frequently measured as a quantitative indicator of damaged material state. Application of higher-order harmonics can improve the sensitivity of detection and monitoring for damages and microstructures due to their higher values of nonlinearity parameters. The excitation and reception of higher-order harmonics, so-called superharmonics, which use the third to fifth harmonics arising from nonlinear wave propagation, is not sufficiently investigated and applied. The purpose of this communication is to develop a highly sensitive superharmonic nondestructive technique that efficiently generates and receives third- and fifth-order harmonics using the odd harmonic resonances of a single piezoelectric crystal. The method focuses on the measurement of fifth harmonic generation and reception, and the calculation of the relative quintic nonlinearity parameter (δ'). The method also addresses the issue of source nonlinearity that may be contained in the measured fifth harmonic amplitude. The measurement results of δ' for a series of precipitation heat-treated samples clearly show a much better sensitivity than the results of the cubic nonlinearity parameter (γ'). The proposed method enables a highly sensitive and true pulse-echo mode nonlinear ultrasound testing.

Macro- and microstructure of lead perovskite ternary piezoelectric single crystals after direct current and alternating current poling

Macro- and microstructure of lead perovskite ternary piezoelectric single crystals after direct current and alternating current poling

Giant Electrostrain in Lead-Free Textured Piezoceramics by Defect Dipole Design.

By converting electrical signal into mechanical displacement, piezoelectric actuators are widely used in many applications due to their precise displacement, fast response, and small size. The unipolar electrostrain values larger than 1% reported so far are from lead-based single crystals or ceramics, which brings environmental concerns. Herein, a giant unipolar electrostrain of 1.6% with good fatigue resistance and low hysteresis in Sr/Nb-doped Bi0.5 (Na0.82 K0.18 )0.5 TiO3 lead-free textured piezoceramics by defect dipole design is reported, which is comparable to or even higher than state-of-the-art lead-based piezoelectric single crystals. The engineered defect dipoles in ergodic relaxor ferroelectrics can introduce a large internal bias field along the poling direction, where the 〈111〉-oriented defect dipoles with large polarizability aligning along the 〈111〉-oriented spontaneous polarizations of the electric-field-induced ferroelectric phase greatly benefit the reversible phase-transition process of the 〈00l〉-textured ceramic. In-depth microstructural studies reveal that the greatly enhanced electrostrain is realized by the synergistic contributions from the reversible electric-field-induced phase transition, grain orientation engineering, and most importantly, defect dipole engineering. The present research provides a general strategy for the design of piezoceramics with high electrostrain, which is expected to be promising alternative to lead-based piezoelectric actuators.

Centimeter-Sized Piezoelectric Single Crystal of Chiral Bismuth-Based Hybrid Halide with Superior Electrostrictive Coefficient.

The lead-free hybrid perovskite piezoelectrics possess advantages of easy processing, light weight, and low-toxicity over inorganic ceramics. However, the lack of understanding in structure-property relationships hinders exploration of new molecular piezoelectric crystals with excellent performances. Herein, by introducing chiral α-phenylethylammonium (α-PEA+ ) cations into bismuth-based hybrid halides, centimeter-sized (R-α-PEA)4 Bi2 I10 and (S-α-PEA)4 Bi2 I10 single crystals with a superior piezoelectric voltage coefficient g22 of 309mV m N-1 , are obtained. Structural rigidity in crystals leads to a remarkable electrostrictive coefficient Q22 of 25.8 m4 C-2 , nearly 20 times higher than that of poly(vinylidene fluoride) (PVDF), which is beneficial to improve piezoelectricity with the synergistic effect of chirality. Moreover, the as-grown crystals show outstanding phase stability from 173 K to ≈470 K. This work suggests a design strategy based on rigidity and chirality to exploit novel piezoelectrics among hybrid metal halides.

Magnetoelectric MEMS Magnetic Field Sensor Based on a Laminated Heterostructure of Bidomain Lithium Niobate and Metglas.

Non-contact mapping of magnetic fields produced by the human heart muscle requires the application of arrays of miniature and highly sensitive magnetic field sensors. In this article, we describe a MEMS technology of laminated magnetoelectric heterostructures comprising a thin piezoelectric lithium niobate single crystal and a film of magnetostrictive metglas. In the former, a ferroelectric bidomain structure is created using a technique developed by the authors. A cantilever is formed by microblasting inside the lithium niobate crystal. Metglas layers are deposited by magnetron sputtering. The quality of the metglas layers was assessed by XPS depth profiling and TEM. Detailed measurements of the magnetoelectric effect in the quasistatic and dynamic modes were performed. The magnetoelectric coefficient |α32| reaches a value of 492 V/(cm·Oe) at bending resonance. The quality factor of the structure was Q = 520. The average phase amounted to 93.4° ± 2.7° for the magnetic field amplitude ranging from 12 to 100 pT. An AC magnetic field detection limit of 12 pT at a resonance frequency of 3065 Hz was achieved which exceeds by a factor of 5 the best value for magnetoelectric MEMS lead-free composites reported in the literature. The noise level of the magnetoelectric signal was 0.47 µV/Hz1/2. Ways to improve the sensitivity of the developed sensors to the magnetic field for biomedical applications are indicated.

Piezoelectric property optimization for piezoelectric single crystals using parametric estimation

ABSTRACT The piezoelectric properties of a piezoelectric single crystal are typically determined using a resonance method. However, it is challenging to evaluate these properties in single crystals owing to their high sensitivity and property variations. In this study, to accurately determine the piezoelectric properties, initial values were obtained using two types of samples (TE and TS modes). Impedance spectrum tendency analysis was performed according to the variables to develop a property estimation method. To determine the reliability of this method, the piezoelectric single crystal properties were evaluated and compared using the resonance method. Hence, it was confirmed that high-accuracy piezoelectric properties were obtained in a cost effective and timeous manner.

Broadband Piezoelectric Energy Harvester Based on Coupling Resonance Frequency Tuning.

The bandwidth of piezoelectric energy harvesters (PEHs) can be broadened by resonance-based frequency tuning approaches, including mechanical tuning and electrical tuning. In this work, a new coupling tuning mechanism for regulating the near-open-circuit resonance frequency by changing the effective electrode coverage (EEC) is presented. A linear model of a bimorph piezoelectric cantilever with segmented electrodes is used to evaluate the power harvesting behavior near the open-circuit resonance frequency when EEC changes from 0 to 100%. According to the theoretical analysis, it is found that the variation of EEC brings about the change in coupling strength, which is positively associated with the near-open-circuit resonance frequency of PEH. Two cantilever PEHs with segmented electrodes based on PZT and PZT-PT are constructed for validation of the coupling tuning mechanism. The analytical and experimental results illustrate remarkable improvements in both bandwidth and average power through the coupling resonance frequency tuning method. In addition, adopting extraordinary piezoelectric single crystals and optimizing the proof mass and piezoelectric layer dimensions were theoretically shown to be effective methods for further improvement of bandwidth.

Comparing Different Electrodes of Piezoelectric Single Crystal Composites for Underwater Acoustic Transducers

Electrodes are critical to piezoelectric single crystal composites (PSCCs) as they directly determine the efficiency and reliability of piezoelectric devices. Currently, a comprehensive comparison of the major properties of different electrodes on PSCCs, particularly their adhesive performance, is highly needed because the cross-linked structure and large surface-displacement fluctuations of PSCCs likely cause the peeling and failure of electrodes. Herein, we compared electronic conductivity and adhesive performance of different electrodes for PSCCs including magnetron sputtering Au (MS Au), electron beam evaporation Au (BE Au), and low-temperature silver paste (LTSP) electrodes. The results demonstrate that the LTSP electrodes exhibited the highest adhesion strength of 3.5 MPa compared to MS Au (2.1 MPa) and BE Au (0.9 MPa) electrodes on PSCCs. In addition, the adhesion strength of electrodes on PSCCs was lower than that on piezoelectric single crystals owing to the existence of the polymer phase. In terms of electrical conductivity, the LTSP electrodes displayed the highest resistivity of 2.25 × 10–6 Ω·m, and MS Au and BE Au electrodes showed similar resistivities of 6.8 × 10–8 and 7.6 × 10–8 Ω·m, respectively. This work provides important information in choosing electrodes for PSCCs, thus benefiting the design for underwater acoustic transducers.