Electromechanical Coupling Factor K33 Research Articles

A high quality lead-free (Li, Ta) modified (K, Na)NbO3single crystal and its complete set of elastic, dielectric and piezoelectric coefficients with macroscopic 4mm symmetry

A high quality orthorhombic (K, Na, Li)(Nb, Ta)O3 single crystal with a large size of 9 × 9 × 11 mm3 was successfully grown using the top-seeded solution growth method. Its large size allowed us to perform comprehensive investigation on this crystal. A complete set of elastic, dielectric and piezoelectric coefficients was determined using combined resonance and ultrasonic methods. The longitudinal piezoelectric coefficient d33 and the transverse piezoelectric coefficient d31 of this lead-free piezoelectric single crystal are as high as 354 pC N−1 and −163 pC N−1, respectively, which are two times higher than those of KNN-TL ceramics and are comparable with those of PZT5. The electromechanical coupling factor k33 is as high as 82%, much higher than those of KNN-TL ceramics and PZT5. The coefficient d33,strain was found to be as high as 672 pm v−1 and the extrinsic contribution (~22%) was investigated by Rayleigh analysis. These high piezoelectric properties make this single crystal a promising candidate for replacing lead-based piezoelectric materials.

Improved thermal stability of [0 0 1]c poled 0.24Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystal with manganese doping

The temperature dependence of dielectric, piezoelectric, and electromechanical coupling properties of 0.5wt.% manganese-doped and undoped [001]c-poled 0.24Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (0.24PIN–0.47PMN–0.29PT) single crystals has been investigated. Compared to the undoped single crystal, the Mn-doped 0.24PIN–0.47PMN–0.29PT demonstrated higher level of coercive field (9.8kV/cm), increased Curie temperature (187°C), improved mechanical quality factor Qm (196), decreased piezoelectric constant d33 and comparable electromechanical coupling factor k33, indicating hardening effects caused by the manganese ion substitution. More importantly, it was found that the Mn substitution significantly enhanced temperature stabilities of k33, d33 and Qm, leading to 30–40°C improvement of the usage temperature range. These results show the application potential of Mn-doped ternary PIN–PMN–PT single crystals for the high-temperature and high-power electromechanical devices.

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.

Comprehensive characterization of surface acoustic wave resonators using relaxor based ferroelectric single crystals

One-port surface acoustic wave resonators (SAW) were fabricated and characterized using Y-cut X propagating relaxor based ferroelectric single crystals of Pb(Mg1/3Nb2/3)O3-33%PbTiO3 and Pb(In1/3Nb2/3)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT). The experimental results demonstrated ultrahigh electromechanical coupling factor K2 of ∼60% for shear horizontal SAW and a relatively strong spurious resonance due to the Rayleigh-type SAW which can be sufficiently suppressed with Au electrode of large thickness. Characteristics of temperature stability, sensitivity to DC bias voltage, and homogeneity for the two resonators were evaluated and compared. The results showed similar instability of domain structure, and PIN-PMN-PT resonators have better temperature stability, but inferior homogeneity compared to that of PMN-33%PT resonators.

Ultrawide-Band Resonators Using Shear Horizontal-Type Plate Wave and Their Application

Currently, mobile or smart phones with multibands and a cognitive radio system require a tunable filter with a wide tunable range to simplify their circuits. An ultrawide-band resonator is an important device to realize the tunable filter. The relative bandwidths (BWs) of 12 to 17% of previously reported surface acoustic wave (SAW) resonators are not sufficient to realize the tunable filter. This time, the authors studied an SH0 mode plate wave in a LiNbO3 plate. As a result, plate wave resonators with a large electro-mechanical coupling factor (k2) of 0.55 (55%), an ultrawide bandwidth of 29%, a high Q of 700, and a large impedance ratio of 98 dB between resonance (fr) and anti-resonance (fa) frequencies were realized for the first time using 27.5–30°YX-LiNbO3 plates. Applying these resonators to a ladder-type tunable filter, a wide tunable range of 19% was obtained.

Comprehensive investigation of elastic and electrical properties of Li/Ta-modified (K,Na)NbO3 lead-free piezoceramics

A full set of elastic and electrical coefficients of (K,Na)NbO3-based lead-free piezoceramics with a nominal composition of Li0.03(K0.48Na0.52)0.97(Nb0.8Ta0.2)O3 (abbreviated as KNNLT) was evaluated by the standard resonance method, and compared to those of K4CuNb8O23 doped (K0.45Na0.55)NbO3 (KNN-KCN) as well as typical Pb(Zr,Ti)O3-based piezoceramics PZT5A. The measurement of intermediate elastic stiffness and compliance coefficients of KNNLT indicated that KNNLT is elastically “softer” than KNN-KCN but “harder” than PZT5A. An extremely high piezoelectric stiffness coefficient h33 = 68.8 × 108 V/m was obtained, due to an especially low clamped dielectric constant ε33S of 361. And a large longitudinal electromechanical coupling factor k33 = 57% was observed in the KNNLT system. Furthermore, the piezoelectric coefficient d33 of KNNLT was characterized via three distinctive methods: the resonance method, the Berlincourt method, and the converse piezoelectric strain measurement; while these three techniques yielded values of 174 pC/N, 195 pC/N, and 308 pm/V, respectively. The difference in d33 values determined by the three methods may be attributed to different measurement frequencies and extrinsic piezoelectric contributions related to domain wall vibration and domain switching. Besides, the piezoelectric performances of KNNLT piezoceramics were found insensitive to frequency but susceptible to temperature and electric field cycling.

Electromechanical properties of relaxor ferroelectric P(VDF-TrFE-CFE)-P(VDF-CTFE) blends

Electromechanical properties of the relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer blended with a small amount of poly(vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] copolymer, which possesses a much higher elastic modulus than that of the neat terpolymer, were investigated. It was observed that the presence of small amount of P(VDF-CTFE) does not affect the microstructure of the crystalline phase. However, the uniaxially stretched blended films show a slight increase in the crystallinity and increased or similar induced polarization at high electric fields compared with the neat terpolymer, likely caused by the interface effect. Consequently, for blends with P(VDF-CTFE) less than 5 wt%, the transverse strains S1 along the stretching direction for uniaxially stretched blended films are nearly the same as those of neat P(VDF-TrFE-CFE), whereas the elastic modulus along the S1-direction increases with the P(VDF-CTFE) content. As a result, the blended films exhibit a higher elastic energy density and electromechanical coupling factor k31 compared with the neat terpolymer.

Nonlinear dielectric response in piezoelectric materials for underwater transducers

SONAR transducers based on single crystal lead magnesium niobate-lead titanate (PMNT) have demonstrated improvements over conventional lead zirconate titanate ceramics. Compositional modifications to PMNT have combined the high piezoelectric coefficient (d33 > 2000 pC/N) and electromechanical coupling factor (k33 > 0.90) with the low mechanical losses (QM > 1000) of “hard” piezoelectric ceramics. The dielectric losses of single crystal PMNT have not been investigated as extensively as the mechanical losses but may significantly affect the performance of a device when water loaded. In this work, nonlinearities in the dielectric permittivity and losses have been investigated as a function of applied electric field, measurement frequency, and temperature. It is shown that electromechanically “hard” single crystals offer greater stability of the dielectric properties while maintaining a high permittivity with respect to conventional lead zirconate titanate ceramics.

Fabrication and Electrical Properties of Mn-Doped KNbO3 Ceramics Synthesized from KHCO3 as a Starting Material

Potassium niobate-based ceramics with 0.1 wt % MnCO3, K(1+x)NbO3+MnCO3 0.1 wt % (KN10000x+Mn, x = 0.0000–0.0010), were fabricated using KHCO3 powder as a starting material. The KN10000x+Mn ceramics were basically fabricated using a conventional ceramic fabrication process and MnCO3 powders were added at the milling stage after the calcination. High density ratios above 95% were prepared for the wide compositional range of excess K amount for KN10000x+Mn ceramics. From these results, Mn ions are thought to act as a sintering aid for KN ceramics. Mn-doped KN10000x ceramics also showed high resisitivities of approximately 1012 Ω cm for the wide variety of x (10000x=0–9). Moreover, the electromechanical coupling factors k33 for KN10000x+Mn had constant values of higher than 0.50.

Calculated Optimal Cuts for SAW Applications of LGS Crystal

Surface acoustic wave(SAW) propagation properties including propagation phase velocity, power flow angle(PFA), anisotropic factor, electromechanical coupling factor(k2) and temperature coefficient of frequency(TCF) are calculated in an optimal region defined by Euler angle (90o,0o~20o,0o~180o) for LGS crystal. It is concluded that the Euler angle (90o, 20o, 122.23o) and (90o, 17.5o, 121.9o) possess superior SAW performance, which have zero PFA, low TCF and moderate k2 simultaneously. We can give priority to these cut-types in the SAW applications at high temperature.

SAW Properties on X,Y,Z-Cut of Sr<sub>3</sub>(Nb,Ta)Ga<sub>3</sub>Si<sub>2</sub>O<sub>14</sub> and Ca<sub>3</sub>(Nb,Ta)Ga<sub>3</sub>Si<sub>2</sub>O<sub>14</sub> Piezoelectric Crystal

We calculate the phase velocity(V), power flow angle(PFA) and electromechanical coupling factor(k2) on X,Y,Z-cut of Sr3NbGa3Si2O14(SNGS),Sr3TaGa3Si2O14 (STGS), Ca3NbGa3Si2O14(CNGS) and Ca3TaGa3Si2O14(CTGS)crystal,. The calculated results are in excellent agreement with the experimental results. As these crystals are denser than quartz, they have lower phase velocity. The results also indicates that they have high k2 and cuts of zero PFA. Taking various SAW properties into consideration, some typical propagation directions like 167.5° of X-cut SNGS ,0 of Y-cut SNGS, 170° of X-cut STGS, 0 of Y-cut STGS,11 of X-cut CNGS, 0 of Y-cut CNGS, 175.0 of X-cut CNGS and 0 of Y-cut CTGS are selected, which can be used in the application of SAW devices.

Engineered domain configuration and piezoelectric energy harvesting in 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals

The performance of cantilever piezoelectric energy harvesters using three types of piezoelectric materials, relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals oriented along the 〈110〉 and 〈001〉 directions, and a PZT-based ceramic, were investigated. The 〈110〉 and 〈001〉 oriented PMN-PT single crystals, which have a rhombohedral phase and spontaneous polarization along the 〈111〉 direction, presented electromechanical coupling factor k31’s of 0.78 and 0.42, respectively. The cantilever-type energy harvester operated by 31 resonance mode generated a larger output power of 1.07 mW for the 〈110〉 oriented PMN-PT single crystal compared to those of the other materials. The effective electromechanical coupling factor of the piezoelectric energy harvester with the 〈110〉 oriented crystal also reached 0.25, not achievable with the other piezoelectric materials. These results demonstrate that the domain engineering of the piezoelectric single crystals can provide higher design flexibility for a tiny energy harvester.

Growth and piezo-/ferroelectric properties of PIN-PMN-PT single crystals

Ternary solid solution crystals of 0.19Pb(In1/2Nb1/2)O3− 0.46Pb(Mg1/3Nb2/3)O3− 0.35PbTiO3 [PIMNT(19/46/35)] with dimensions of 35 × 38 × 15 mm3 were grown by the top-seeded solution growth (TSSG) method. The dielectric, piezo- and ferroelectric properties of the grown crystals were characterized. The ternary piezocrystals exhibit a Curie temperature TC = 190 °C and a tetragonal-rhombohedral phase transition temperature TR-T = 130 °C, which are increased significantly compared with TC ≈ 155 °C and TR-T ≈ 80 °C of PMN-PT crystals. The dielectric constant (ɛ′) and dielectric loss tangent (tan δ) are 4300 and 0.40 at room temperature. The piezoelectric coefficient d33 is found to be 2380 pC/N. The longitudinal electromechanical coupling factor k33 reaches 90% at room temperature. A peak-to-peak bipolar strain value of 0.13% is obtained at E ≈ ± 14 kV/cm. The coercive field Ec and remanent polarization Pr are 5.50 kV/cm and 27.10 μC/cm2, respectively, which are also improved from the vales of PMN-PT crystals.

Ultra-wideband surface acoustic wave resonator employing Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Theoretical analysis showed that high performance surface acoustic wave (SAW) resonator with an extremely large electromechanical coupling factor K2 could be realized on Y cut X propagating Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (YX-PIN-PMN-PT) substrate. A one-port SAW resonator was designed, fabricated, and characterized on Cu-grating/YX-PIN-PMN-PT substrate structure. The experimental results demonstrate that very large K2 of 57.3% is realizable. Such an extremely large K2 makes PIN-PMN-PT single crystal great potential for realizing wideband SAW filters and tunable SAW filters. The influence of inhomogeneity and instability of the domain structure on the fabricated resonators has been discussed thoroughly for further improvement of the devices.

Progress in lead-based ferroelectric and antiferroelectric single crystals: composition modification, crystal growth and properties

Ferroelectric and antiferroelectric materials, with complex perovskite structures, have experienced wide interest due to their peculiar structure and properties. In this highlight, recent advances of these two types of materials are reviewed, with particular emphasis on piezoelectrics/ferroelectric and antiferroelectric single crystals, owing to their ultra-high electric properties for practical application. Relaxor ferroelectric single crystals, represented by Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) at compositions near the morphotropic phase boundary (MPB), possess a high piezoelectric constant d33 (>2000 pC N−1) and electromechanical coupling factors k33 (90–92%). However, a low ferroelectric phase transition temperature Tr-t, far below the Curie temperature Tc restricts its further application in a broad temperature range. Some work on the design of a new pseudo-ternary system of Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMN-PZ-PT) and Pb(Mg1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–PbTiO3 (PMN-PFN-PT) have been demonstrated with emphasis on the composition modification and crystal growth. Moreover, for relaxor antiferroelectrics represented by (Pb,La)(Zr,Sn,Ti)O3 (PLZST) it is very difficult to grow bulk and high quality single crystals because of its incongruent melting. Our recent investigations on the flux growth of PLZST single crystals, especially the flux selection, compositions optimization, and defect analysis of as-grown single crystals are also described in this highlight.

Growth of Pb(Fe1/2Nb1/2)O3–Pb(Yb1/2Nb1/2)O3–PbTiO3 piezo-/ferroelectric crystals for high power and high temperature applications

In order to develop new piezoelectric crystals with high TC and high performance for high-power and high-temperature applications, the Pb(Fe1/2Nb1/2)O3–Pb(Yb1/2Nb1/2)O3–PbTiO3 [PFN–PYN–PT(10/38/52)] ternary piezo-/ferroelectric single crystals have been grown by the flux method for the first time. The crystal structure has been characterized by means of X-ray diffraction technique, showing a perovskite phase with rhombohedral symmetry at room temperature. The as-grown PFN–PYN–PT crystal possesses a high Curie temperature (TC) of 325 °C and a high rhombohedral-tetragonal phase transition temperature (Trt) of 155 °C. Complete electric characterization has revealed the high performance of the ternary crystals, with a dielectric constant e′ = 1620, a piezoelectric coefficient d33 = 1100 pC N−1, a longitudinal electromechanical coupling factor k33 = 70%, a remnant polarization Pr = 25.8 μC cm−2, a coercive field Ec = 10.3 kV cm−1, and a mechanical quality factor Qm = 110 for (001)-oriented crystals at room temperature. These results show that the PFN–PYN–PT crystals are a promising candidate for uses in electromechanical transducers for high-power and high-temperature applications.

Use of fluorine-doped silicon oxide for temperature compensation of radio frequency surface acoustic wave devices

This paper investigates acoustic properties, including the temperature coefficient of elasticity (TCE), of fluorine-doped silicon oxide (SiOF) films and proposes the application of the films to the temperature compensation of RF SAW devices. From Fourier transform infrared spectroscopy (FT-IR), SiOF films were expected to possess good TCE properties. We fabricated a series of SAW devices using the SiOF-overlay/Cu-grating/LiNbO(3)-substrate structure, and evaluated their performance. The experiments showed that the temperature coefficient of frequency (TCF) increases with the fluorine content r, as we expected from the FT-IR measurement. This means that the Si-O-Si atomic structure measurable by the FT-IR governs the TCE behavior of SiO(2)-based films even when the dopant is added. In comparison with pure SiO(2) with the film thickness h of 0.3 wavelengths (λ), TCF was improved by 7.7 ppm/°C without deterioration of the effective electromechanical coupling factor K2 when r = 3.8 atomic % and h = 0.28λ. Fluorine inclusion did not obviously influence the resonators' Q factors when r < 8.8 atomic %.

Design of narrow bandwidth elliptic-type SAW/BAW filters

The passband width obtained in the SAW/BAW filter is inherently limited by the electromechanical coupling factor K2 of piezoelectric substrate. Proposed is a new design technology to flexibly control the passband width without sacrificing insertion loss, out-of-band rejection and steepness of the transition bands. A bandpass LC filter has been designed based on the traditional elliptic filter design. The LC resonators are replaced with SAW/BAW resonators in this filter and the design of the resonators is optimised to suppress passband ripples generated by finite capacitance ratio γ. It revealed that filters with different relative bandwidth are easy to design using one piezoelectric substrate. This technique is applied to the design of a SAW filter fabricated on the Cu-grating/15°YX-LiNbO3 structure.

Hydrostatic Pressure Dependence of Dielectric, Elastic, and Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 Ceramic

The effect of hydrostatic pressure on piezoelectric materials is a crucial factor for underwater device design. In this work, the dielectric, elastic, and piezoelectric properties of Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 [PMNT (67/33)] ceramics were investigated under pressure from 0.1 to 455 MPa. The dielectric permittivity and losses were found to increase under hydrostatic pressure due to enhanced domain wall motion. With increasing hydrostatic pressure, the mechanical losses drastically increased, which can be attributed to the increase of both domain wall motion and the friction between pressure‐transmitting fluid and piezoelectric vibrators. In addition, piezoelectric coefficients (d33, d31) and electromechanical coupling factors (k33, k31) were found to decrease with increasing pressure, owing to the pressure‐induced depolarization for PMNT ceramics.

Elastic, piezoelectric, and dielectric properties of Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3Pb-free ceramic at the morphotropic phase boundary

There is an urgent demand for high performance Pb-free piezoelectrics to substitute for the current workhorse, the lead zirconate titanate (PZT) family. Recently, a triple point (also tricritical point) type morphotropic phase boundary (MPB) in Pb-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 system has been reported that shows equally as excellent piezoelectricity as soft PZT at room temperature (Liu and Ren6). In the present study, we measured a full set of elastic, piezoelectric, and dielectric properties for the MPB composition, Ba(Zr0.2Ti0.8)O3-50(Ba0.7Ca0.3)TiO3 (BZT-50BCT), by using a resonance method. The resonant method gives piezoelectric properties d33 = 546 pC/N, g33 = 15.3 × 10−3 Vm/N, electromechanical coupling factor k33 = 65%, and the elastic constant s33E = 19.7 × 10−12 m2/N, c33E = 11.3 × 1010 N/m2, which are close to the properties of soft PZT (PZT-5A). Furthermore, the piezoelectric coefficients (k33, d33), the ferroelectric properties (coercive field, remnant polarization), and the elastic ...