Piezoelectric Single Crystals Research Articles

Determination of the complex material constants of PMN–28%PT piezoelectric single crystals

The accurate characterization of piezoelectric crystals should include the loss properties of the materials, which are represented as the imaginary parts of the material constants. The full complex properties of PMN–PT single crystals have never been evaluated. This paper proposes an automated iterative method to determine the complex material constants of PMN–28%PT single crystals. The PMN–28%PT single crystals were grown using the Bridgman method and were poled along the [001] direction to have 4mm effective symmetry. Five different resonators suitable for 4mm symmetry were used to analyze the impedance and admittance spectra of the distinctive resonant modes. The complex material constants were determined by the nonlinear regression of the impedance and admittance spectrum equations for each resonator through the iteration process to fit the measured spectra of the corresponding modes. The efficacy of the characterization method and the accuracy of the complex material constants determined using this method were verified by a comparison of the immittance spectra from the measurements with those from the calculation using the complex constants.

Growth and properties of Li, Ta modified (K,Na)NbO3 lead-free piezoelectric single crystals.

Li, Ta modified (K,Na)NbO3 single crystals with the size of 18 mm × 18 mm × 10 mm were successfully grown by top-seeded solution growth method, with orthorhombic-tetragonal phase transition temperature ~79 °C and Curie temperature ~276 °C. The electromechanical coupling factors k33 and kt were found to be ~88% and ~65%, respectively. The piezoelectric coefficient d33 for the [001]c poled crystals reached 255 pC/N. In addition, the electromechanical coupling factor exhibited high stability over the temperature range of -50 °C to 70 °C, making these lead free crystals good candidates for electromechanical applications.

Growth of (K0.5Na0.5)NbO3–SrTiO3 lead-free piezoelectric single crystals by the solid state crystal growth method and their characterization

Lead zirconate titanate (PZT) piezoelectric ceramics are commonly used in various applications, e.g. gas igniters, high-voltage generators and microbalances. However, due to increasing health and environmental concerns over their high lead content, lead-free piezoelectric ceramics are being developed. Lead-free piezoelectric single crystals offer superior performance over their polycrystalline counterparts but are difficult to grow by conventional methods. In this paper, (K0.5Na0.5)NbO3–SrTiO3 (KNN–ST) single crystals are grown for the first time by the solid state crystal growth (SSCG) method. 〈100〉 KTaO3 single crystal seeds are buried in the center of pellets of pressed KNN-ST powder. The single crystal grows from the seed crystal during sintering at 1100°C for 20h. The grown single crystals contain porosity, which is incorporated from the matrix during growth. The effect of SrTiO3 addition on single crystal growth behavior, chemical composition and structure is evaluated.

Dielectric properties in lead-free piezoelectric (Bi0.5Na0.5)TiO3–BaTiO3 single crystals and ceramics

The 0.93(Bi0.5Na0.5)TiO3–0.07BaTiO3 (BNB7T) piezoelectric single crystals and ceramics have been grown respectively by using the self-flux and solid-state-reaction methods. The real (ε′) and imaginary (ε″) parts of the dielectric permittivity of BNB7T crystals and ceramics were investigated with and without an electric (E) poling as functions of temperature and frequency. The BNB7T crystal shows a stronger dielectric maximum at Tm~240°C than the ceramic at Tm~300°C. The dielectric permittivity of BNB7T ceramic shows an extra peak after poling at an electric field E=40kV/cm in the region of 80–100°C designated as the depolarization temperature (Td). A wide-range dielectric thermal hysteresis was observed in BNB7T crystal and ceramic, suggesting a first-order-like phase transition. The dielectric permittivity ε′ obeys the Curie–Weiss equation, ε′=C/(T−To), above 500°C, which is considered as the Burns temperature (TB), below which polar nanoregions begin to develop and attenuate dielectric responses.

Complete set of material constants of 0.95(Na0.5Bi0.5)TiO3-0.05BaTiO3 lead-free piezoelectric single crystal and the delineation of extrinsic contributions

Lead-free piezoelectric single crystal 0.95(Na0.5Bi0.5)TiO3 (NBT)-0.05BaTiO3 was grown by top-seeded solution growth method, which has rhombohedral symmetry with composition near morphotropic phase boundary. Full set of dielectric, piezoelectric, and elastic constants for [001]c poled domain-engineered single crystal was determined. Excellent electromechanical properties and low dielectric loss (d33 = 360 pC/N, d31 = −113 pC/N, d15 = 162 pC/N, k33 = 0.720, kt = 0.540, and tan δ = 1.1%) make it a good candidate to replace lead-based piezoelectric materials. The depolarization temperature (Td = 135 °C) is the highest among all NBT-based materials and its electromechanical coupling properties are very stable below Td. Extrinsic contributions to piezoelectric properties were investigated by Rayleigh analysis.

Growth and Characterization of Ca2Al2SiO7 Piezoelectric Single Crystals for High-Temperature Sensor Applications

The electrical properties of a piezoelectric single crystal of calcium aluminate silicate Ca2Al2SiO7 (CAS) were studied at elevated temperatures and its applicability to high-temperature pressure sensors was investigated. The CAS bulk single crystal was grown by the Czochralski method. The piezoelectric d14 and d36 constants were respectively evaluated as 6.04 and 4.04 pC/N by the resonance and antiresonance method. The temperature dependence of the piezoelectric constant was investigated at temperatures up to 500 °C. The electrical resistivity at 800 °C was on the order of 108 Ω·cm along both the crystallographic a- and c-axes. The measurement of direct piezoelectric response at 700 °C demonstrated that the CAS crystal could detect a pseudo-combustion pressure change of an automobile engine. Our observations suggest that CAS crystals are superior candidates for sensing pressure at high temperatures.

Radiation from 20 MeV electrons in piezoelectric single crystals in the presence of external acoustic fields

The radiation from electrons interacting with piezoelectric single crystals and the influence of acoustic fields on the frequency-temporal parameters of characteristic energy yields have been investigated experimentally. The experiments were carried out on the extracted 20 MeV electron beam of the linear accelerator LEA-50 of the Alikhanian National Scientific Laboratory. The energy distributions of specific yields of the electron radiation in quartz single crystal were obtained. The amplification of intensity and the shift of energy yields under the influence of hypersonic vibrations were observed.

1.75D 초음파 트랜스듀서의 설계 및 제작

In this paper, a channel 1.75D ultrasonic transducer made of piezoelectric single crystals was designed, fabricated, and evaluated. First, a structure of the transducer was selected to be suitable for wiring on a planar array, and components were fabricated to correspond to the structure. Detailed structure of the transducer was designed through finite element analyses. As main performance factors, the crosstalk between neighboring elements was reduced through the control of kerf width and material, and desired frequency bandwidth of the transducer was achieved by designing the optimal thicknesses of the piezoelectric single crystal and matching layers. An experimental prototype of the transducer was fabricated following the design, and its performance was measured. Then the experimental results were compared with those of the finite element analysis, which led to the evaluation of the transducer developed in this work.

Ultra-low frequency underwater acoustic projectors: Present status and future trends

Ultra-low frequency (ULF) underwater transducers, used in the 10–400 Hz frequency range, have usually radiating surfaces the dimensions of which are small with respect to the acoustic wavelength. To radiate a high acoustic power with a monopolar ULF transducer, a large volume velocity is required to counterbalance the low radiation resistance. Three transduction technologies are available to realize compact high power ULF transducers: hydroacoustic, electromagnetic, and active material-based. In the latter case, piezoelectric ceramics and magnetostrictive rare-earth alloys are often associated to flexural vibration such as found in flextensional transducers. Compared to these materials, piezoelectric single crystals, which exhibit lower stiffnesses and produce higher strains together with higher energy densities, are potential active materials for future ULF underwater transducers. In this work, ULF transducers are analyzed in terms of their working frequencies, acoustic powers, and masses. Thirty-two ULF underwater projectors build during the last 25 years are considered. For single crystal transducers, prototypes working at higher frequencies as well as transducers modeled with finite element method are taken into account. Using these data and classical scaling laws, abacuses displaying acoustic power-frequency curves for given masses are constructed for each technology. They show that single crystals transducers could provide more compact and powerful solutions for frequencies above 40 Hz.

Apparatus for measurement of acoustic wave propagation under uniaxial loading with application to measurement of third-order elastic constants of piezoelectric single crystals

We describe an apparatus for the measurement of acoustic wave propagation under uniaxial loading featuring a special mechanism designed to assure a uniform mechanical load on a cube-shaped sample of piezoelectric material. We demonstrate the utility of the apparatus by determining the effects of stresses on acoustic wave speed, which forms a foundation for the final determination of the third-order elastic constants of langasite and langatate single crystals. The transit time method is used to determine changes in acoustic wave velocity as the loading is varied. In order to minimize error and improve the accuracy of the wave speed measurements, the cross correlation method is used to determine the small changes in the time of flight. Typical experimental results are presented and discussed.

Plastic deformation of piezoelectric lanthanum-gallium tantalate crystals during cyclic mechanical actions

The microstructure of piezoelectric lanthanum-gallium tantalite single crystals is shown to change substantially during cyclic mechanical actions at room temperature and during thermal shock: the dislocation density increases, twinning takes place, and a mesostructure forms. This effect is related to the appearance of piezoelectric fields, which significantly decrease the temperature of the onset of plastic deformation of these brittle single crystals, during mechanical actions.

Design and Fabrication of a 2D Array Ultrasonic Transducer

본 논문에서는 <TEX>$48{\times}64$</TEX> 채널로 이루어진 압전단결정 2D 배열형 초음파 트랜스듀서의 설계, 제작 및 평가를 하였다. 전기적 연결이 용이한 평면배열 구조를 선정한 후, 그에 맞게 구성소자를 제작하였다. 유한요소 해석을 통하여 트랜스듀서의 세부 구조를 설계하였다. 트랜스듀서의 성능을 향상시키기 위해 치폭의 너비와 재료를 조절하여 소자간 상호간섭을 저감하고, 압전단결정 및 정합층의 최적 두께를 설계하여 목표 주파수 대역폭을 구현하였다. 설계에 따라 트랜스듀서의 시작품을 제작하고 그 특성을 측정한 후, 측정된 결과를 유한요소 해석 결과와 비교하여 개발된 트랜스듀서의 성능을 평가하였다. In this paper, a <TEX>$48{\times}64$</TEX> channel 2D array ultrasonic transducer with piezoelectric single crystals was designed, fabricated, and evaluated. Structure of the transducer was chosen to facilitate the electric connection on the planar array, and then components were fabricated in accordance with the structure. Detailed structure of the transducer was designed through finite element analyses. In order to improve the performance of the transducer, the crosstalk between adjacent elements was reduced through the control of kerf width and material, and the target frequency bandwidth was achieved through optimal design of the thickness of the single crystal and matching layers. After fabricating a prototype of the transducer according to the design and measuring its characteristics, the results were compared with those of finite element analyses to evaluate the performance of the developed transducer.

Large size lead-free (Na,K)(Nb,Ta)O3 piezoelectric single crystal: growth and full tensor properties

Environmental friendly piezoelectric single crystal, Ta-modified (K,Na)NbO3 with the size of 12 × 11 × 11 mm3, has been successfully grown using the top seeded solution growth technique. This orthorhombic phase (K,Na)(Nb,Ta)O3 single crystal is the largest size to date in KNN-based crystals with homogeneous composition. The large size allowed us to apply the domain engineering technique to further enhance its piezoelectric properties. In addition, a self-consistent complete set of elastic, dielectric and piezoelectric constants for the [001]c poled domain engineered crystal has been measured, which is urgently needed for theoretical studies and simulation designs of electromechanical devices using this lead-free piezoelectric material. The electromechanical coupling factors are very high (k33 = 0.827, kt = 0.646) and the dielectric loss tangent is as low as 0.004 for this lead-free piezoelectric crystal. Such excellent properties make this crystal an excellent candidate to replace lead-containing piezoelectric materials in electromechanical devices.

Medical Applications of Piezoelectric Microelectromechanical Systems

Bulk piezoelectric ceramics and single crystals are widely used in medical applications, including medical ultrasonic imaging, therapeutic ultrasound, and drug delivery. This paper reviews possibilities for thin film micromachined components as alternatives to the bulk devices. Particular emphasis is placed on the development of a CMOS-compatible ultrasound system. For this purpose, a piezoelectric ultrasound system on a Si substrate was fabricated using a diaphragm geometry transducer with PZT films. A 1-D array of 8 elements was designed and fabricated using 4 photolithography steps. Cavities under the resonating elements were obtained by XeF2 etching from the top-side of the wafer. Capacitance and admittance spectra showed a resonance at ∼ 42 MHz for the fabricated structures with a quality factor of 2.1, this resonance was higher than the one predicted by the natural frequency equation for circular plate. Catch- and pitch-mode tests were performed in water. Sensing and actuating functionalities were demonstrated for the fabricated devices, with collected signals of 40 mV peak-to-peak at a distance of 7.2 mm during the catch-mode test and amplitudes as high as 15 mV peak-to-peak at a distance of 7.4 mm during the pitch-mode test. A bandwidth of 83% was calculated during pitch-mode test.

Evaluation of All the Material Constants of PMN-28%PT Piezoelectric Single Crystals for Acoustic Transducers

Evaluation of All the Material Constants of PMN-28%PT Piezoelectric Single Crystals for Acoustic Transducers

Crystal structure, dielectric properties of (K0.5Na0.5)NbO3 single crystal grown by flux method using B2O3 flux

AbstractLead free piezoelectric single crystals of sodium potassium niobate (K0.5Na0.5)NbO3 (KNN) were grown by high‐temperature solution method using two different fluxes; one with a mixture of NaF and KF and other with addition of B2O3 along with the mixture. In the present study, the growth of KNN crystals without B2O3 flux and the same with B2O3 flux were compared. It was found that additions of small amounts of B2O3 lowered the melting temperature of the solid solution and enabled better dielectric properties. Phase analysis showed that all samples were crystallized in pure orthorhombic perovskite phase. AFM morphological studies showed that the addition of B2O3 flux increased the roughness of the grown crystal. Further, addition of B2O3 flux slightly decreased the orthorhombic to tetragonal phase transition temperature T(O—T) and the Curie temperature TC. The ferroelectric behaviour of KNN single crystal has been investigated at room temperature. The crystal grown using B2O3 flux exhibited a remanent polarization (Pr) ∼ 32 μC/cm2 and coercive field (Ec) of ∼11.8 kV/cm whereas the crystal grown without the use of B2O3 flux had a remanent polarization (Pr) ∼ 36 μC/cm2 and coercive field (Ec) of ∼14.6 kV/cm.

Electrically Tunable Resonator for Microwave Applications Based on Hexaferrite-Piezoelectrc Layered Structure

An electrically tunable micro wave resonator based on bilayers with single crystal Zn2Y-type hexaferrite and piezoelectrics of Lead Zirconate Titanate or Lead Magnesium Niobate - Lead Titanate is investigated. The resonator was positioned in a microstripline antenna structure based on alumina substrate. Resonance profiles were obtained for electric field E=0-12 kV/cm; bias magnetic fields H was parallel to the basal plane of hexaferrite. The magnetic and electric tunings of the resonator has been measured. Experimental and theoretical data of research are presented in the frequency range 5-25 GHz.

Growth of column-shaped and plate-like langasite-type piezoelectric single crystals and their physical properties

Column-shaped Ca3TaGa3Si2O14 (CTGS) and plate-like Ca3NbGa3Si2O14 (CNGS) single crystals were grown by micro-pulling-down method using crucibles of original shape. The column-shaped CTGS crystals oriented along a- and c-axes were produced using the seeds of corresponding orientations. The plate-like CNGS crystal was grown along a-axis from the crucible equipped with a plate-shaped die at the bottom. The X-ray diffraction patterns of the grown CTGS and CNGS crystals corresponded to langasite-type structure and the lattice parameters were consistent with those of the crystals grown by Czochralski (Cz) method. The X-ray rocking curve analysis indicated that structural perfection of the grown CTGS and CNGS shaped crystals was comparable to that of the crystals produced by Cz method. The central part of the CTGS crystal was single phase material and had excess of Ca and Si with corresponding deficit of Ta and Ga. However, peripheral parts of the crystal contained secondary phase of calcium tantalate. In the transmission spectrum, two broad absorption peaks around 360 and 490nm were observed that was associated with the color centers relevant to the oxygen content in the crystal.

Effect of B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Flux on the Crystal Structure, Dielectric Properties of (K &lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;)NbO&lt;sub&gt;3&lt;/sub&gt; Single Crystal Grown by Flux Method

Lead free piezoelectric single crystals of sodium potassium niobate (K 0.5Na0.5)NbO3 single crystals were grown by high-temperature solution method using B2O3 flux The KNN crystals grown by without B2O3 flux and with B2O3 flux are referred to as samples A and B respectively. It was found that additions of small amounts of boron oxide B2O3 further lower the melting temperature of the eutectic mixture and exhibits excellent dielectric properties. Phase analysis showed that all samples crystallized in pure orthorhombic perovskite phase. AFM morphological studies show that the root mean square (rms) roughness values were measured to be, 5.3nm and 6.96nm for the sample A and sample B crystal respectively. A slight decrease in the orthorhombic to tetragonal phase transition temperature TOT&gt; and Curie temperature Tc has been observed in sample B when compared with sample A.

Growth and electrical properties of 0.88Na0.5Bi0.5TiO3–0.12K0.5Bi0.5TiO3 lead-free piezoelectric single crystal

A large-size 0.88Na0.5Bi0.5TiO3–0.12K0.5Bi0.5TiO3 lead-free piezoelectric single crystal with dimensions of ∅30 mm ×10 mm was successfully grown by the top-seeded solution growth method. X-ray powder diffraction measurement showed that the as-grown crystal possesses a rhombohedral perovskite structure at room temperature. The temperature dependence of dielectric constant and loss, polarization hysteresis loop, electric-field-induced strain, and the electromechanical coupling property were investigated for the -oriented as-grown crystal. The remanent polarization Pr, the piezoelectric constant d33, and the electromechanical coupling coefficient kt at room temperature are 13.8 pC/cm2, 205 pC/N, and 51 %, respectively. The maximum strain of 0.23 % was obtained under 30 kV/cm. The temperature dependence of kt demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 20–150 °C.