Showing papers on "Piezoelectricity published in 2009"

A Strain-Driven Morphotropic Phase Boundary in BiFeO3

Abstract: Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.

Dielectric and Piezoelectric Properties in Mn‐Modified (1−x)BiFeO3–xBaTiO3 Ceramics

Abstract: In the current work, the bulk (1−x)BiFeO3–xBaTiO3 system has been studied as a potential lead-free piezoelectric material. Barium titanate (BaTiO3) in solid solution with bismuth ferrite (BiFeO3) is observed to stabilize the perovskite structure and improve switching behavior. Samples with various content of BaTiO3 were prepared via solid-state route, and pure perovskite phase was confirmed by X-ray diffraction. Modification of the BaTiO3–BiFeO3 material with Mn improved DC resistivity by one to five orders of magnitude (7.6 × 1012 vs. 2.7 × 107Ω·m for 25 mol% BaTiO3 at room temperature) and polarization hysteresis measurements indicated “hard” ferroelectric behavior with the highest strain response at 33 mol% BaTiO3. Finally, low-field piezoelectric d33 coefficient of 116 pC/N and ferroelectric transition temperature above 450°C are reported for 25 mol% BaTiO3 composition.

Electric-field-induced phase transformation at a lead-free morphotropic phase boundary: Case study in a 93%(Bi0.5Na0.5)TiO3–7% BaTiO3 piezoelectric ceramic

Abstract: The electric-field-induced strain in 93%(Bi0.5Na0.5)TiO3–7%BaTiO3 polycrystalline ceramic is shown to be the result of an electric-field-induced phase transformation from a pseudocubic to tetragonal symmetry. High-energy x-ray diffraction is used to illustrate the microstructural nature of the transformation. A combination of induced unit cell volumetric changes, domain texture, and anisotropic lattice strains are responsible for the observed macroscopic strain. This strain mechanism is not analogous to the high electric-field-induced strains observed in lead-based morphotropic phase boundary systems. Thus, systems which appear cubic under zero field should not be excluded from the search for lead-free piezoelectric compositions.

Equilibrium Potential of Free Charge Carriers in a Bent Piezoelectric Semiconductive Nanowire

Abstract: We have investigated the behavior of free charge carriers in a bent piezoelectric semiconductive nanowire under thermodynamic equilibrium conditions. For a laterally bent n-type ZnO nanowire, with the stretched side exhibiting positive piezoelectric potential and the compressed side negative piezoelectric potential, the conduction band electrons tend to accumulate at the positive side. The positive side is thus partially screened by free charge carriers while the negative side of the piezoelectric potential preserves as long as the donor concentration is not too high. For a typical ZnO nanowire with diameter 50 nm, length 600 nm, donor concentration N(D) = 1 x 10(17) cm(-3) under a bending force of 80 nN, the potential in the positive side is <0.05 V and is approximately -0.3 V at the negative side. The theoretical results support the mechanism proposed for a piezoelectric nanogenerator. Degeneracy in the positive side of the nanowire is significant, but the temperature dependence of the potential profile is weak for the temperature range of 100-400 K.

Giant Electric Field Tuning of Magnetism in Novel Multiferroic FeGaB/Lead Zinc Niobate–Lead Titanate (PZN-PT) Heterostructures

Abstract: Multiferroic composite materials consisting of both a magnetic phase and a ferroelectric phase are of great current interest, as they offer the possibility ofmagnetoelectric (ME) coupling, that is, electric field manipulation of magnetic properties (converse ME effect) or vice versa (direct ME effect), and have led to many novel multiferroic devices. One important series of such multiferroic devices is constituted by electrostatically tunable microwave multiferroic signal processing devices, including tunable resonators, phase shifters, and tunable filters. Compared to conventional tunable microwave magnetic devices, which are tuned by magnetic fields, these electrostatically tunable microwave multiferroic devices are much more energy efficient, less noisy, compact, and lightweight. ME effects can be realized in multiferroic composites through a strain/stress-mediated interaction, which enables effective energy transfer between electric and magnetic fields and leads to important new functionalities and devices. Strong ME coupling is critical for multiferroic devices; however, it has been difficult to achieve at microwave frequencies, leading to a very limited tunability in electrostatically tunable microwave multiferroic devices. The demonstrated tunable range of most of these devices has been very limited, with a frequency tunability of Df< 150MHz and a low tunable magnetic field of DH< 50Oe (1 Oe 79.6 A m ). This is mainly due to the large loss tangents at microwave frequencies of the two constituent phases, that is, the ferroelectric phase and, particularly, the magnetic phase, which is less resistive. The ME coupling strength in multiferroic composites is determined by many factors, such as the properties of the two constituent phases, the interface between them, the mode of ME coupling, and the orientation of the magnetic and electric fields. As a result, layered multiferroic heterostructures with magnetic thin films provide great opportunities for achieving strong ME coupling at microwave frequencies, owing to minimized charge leakage paths and low loss tangents associated with magnetic thin films. It is also desirable for the magnetic phase in the multiferroic composites to have a narrow ferromagnetic resonance (FMR) linewidth and a large piezomagnetic coefficient (dl/dH), that is, a large saturation magnetostriction constant (ls) and a low saturation magnetic field (Hs). However, suchmagnetic materials have not been readily available. Very recently, we have reported a new class of metallic magnetic FeGaB films that has a high ls of ca. 70 ppm, a lowHs of ca. 20Oe, and a narrow FMR linewidth of ca. 16Oe at X-band (ca. 9.6GHz). The maximum piezomagnetic coefficient of the FeGaB films is about 7 ppm Oe , which is much higher than those of other well-known magnetostrictive materials used in multiferroic composites, such as Terfenol-D (Tb-Dy-Fe), Galfenol (Fe-Ga), and Metglas (FeBSiC), as shown in Figure 1. The combination of narrow FMR linewidth and high piezomagnetic coefficient makes these FeGaB films excellent candidates for the magnetic material in microwave multiferroic composites. Single-crystal ferroelectrics such as lead magnesium niobate–lead titanate (PMN-PT) and lead zinc niobate–lead titanate (PZN-PT) having giant piezoelectric coefficients and low loss tangents are desired for microwave multiferroic composites as well. In particular, (011)-cut PMN-PT and PZN-PT single-crystal slabs have anisotropic piezoelectric coefficients d31 and d32 when poled along their [011] crystalline direction. For example, (011)-cut PZN-PT single crystals with 6% lead titanate have high anisotropic piezoelectric coefficients d311⁄4 3000 pC N 1 and d321⁄4 1100 pC N . The giant anisotropic piezoelectric coefficients of the PZN-PTsingle crystal provide great opportunities for generating a large in-plane magnetic anisotropic field and

Piezoelectric Thin Films for Sensors, Actuators, and Energy Harvesting

Abstract: Piezoelectric microelectromechanical systems (MEMS) offer the opportunity for high-sensitivity sensors and large displacement, low-voltage actuators. In particular, recent advances in the deposition of perovskite thin films point to a generation of MEMS devices capable of large displacements at complementary metal oxide semiconductor-compatible voltage levels. Moreover, if the devices are mounted in mechanically noisy environments, they also can be used for energy harvesting. Key to all of these applications is the ability to obtain high piezoelectric coefficients and retain these coefficients throughout the microfabrication process. This article will review the impact of composition, orientation, and microstructure on the piezoelectric properties of perovskite thin films such as PbZr1−xTixO3 (PZT). Superior piezoelectric coefficients (e31, f of −18 C/m2) are achieved in {001}-oriented PbZr0.52Ti0.48O3 films with improved compositional homogeneity on Si substrates. The advent of such high piezoelectric responses in films opens up a wide variety of possible applications. A few examples of these, including low-voltage radio frequency MEMS switches and resonators, actuators for millimeter-scale robotics, droplet ejectors, energy scavengers for unattended sensors, and medical imaging transducers, will be discussed.

Atomistic determination of flexoelectric properties of crystalline dielectrics

Abstract: Upon application of a uniform strain, internal sublattice shifts within the unit cell of a noncentrosymmetric dielectric crystal result in the appearance of a net dipole moment: a phenomenon well known as piezoelectricity. A macroscopic strain gradient on the other hand can induce polarization in dielectrics of any crystal structure, even those which possess a centrosymmetric lattice. This phenomenon, called flexoelectricity, has both bulk and surface contributions: the strength of the bulk contribution can be characterized by means of a material property tensor called the bulk flexoelectric tensor. Several recent studies suggest that strain-gradient induced polarization may be responsible for a variety of interesting and anomalous electromechanical phenomena in materials including electromechanical coupling effects in nonuniformly strained nanostructures, ``dead layer'' effects in nanocapacitor systems, and ``giant'' piezoelectricity in perovskite nanostructures among others. In this work, adopting a lattice dynamics based microscopic approach we provide estimates of the flexoelectric tensor for certain cubic crystalline ionic salts, perovskite dielectrics, $III\text{\ensuremath{-}}V$ and $II\text{\ensuremath{-}}VI$ semiconductors. We compare our estimates with experimental/theoretical values wherever available and also revisit the validity of an existing empirical scaling relationship for the magnitude of flexoelectric coefficients in terms of material parameters. It is interesting to note that two independent groups report values of flexoelectric properties for perovskite dielectrics that are orders of magnitude apart: Cross and co-workers from Penn State have carried out experimental studies on a variety of materials including barium titanate while Catalan and co-workers from Cambridge used theoretical ab initio techniques as well as experimental techniques to study paraelectric strontium titanate as well as ferroelectric barium titanate and lead titanate. We find that, in the case of perovskite dielectrics, our estimates agree to an order of magnitude with the experimental and theoretical estimates for strontium titanate. For barium titanate however, while our estimates agree to an order of magnitude with existing ab initio calculations, there exists a large discrepancy with experimental estimates. The possible reasons for the observed deviations are discussed.

Multimodal Energy Harvesting System: Piezoelectric and Electromagnetic:

Abstract: In this study, we report a multimodal energy harvesting device that combines electromagnetic and piezoelectric energy harvesting mechanism. The device consists of piezoelectric crystals bonded to a cantilever beam. The tip of the cantilever beam has an attached permanent magnet which, oscillates within a stationary coil fixed to the top of the package. The permanent magnet serves two purpose (i) acts as a tip mass for the cantilever beam and lowers the resonance frequency, and (ii) acts as a core which oscillates between the inductive coils resulting in electric current generation through Faraday's effect. Thus, this design combines the energy harvesting from two different mechanisms, piezoelectric and electromagnetic, on the same platform. The prototype system was optimized using the finite element software, ANSYS, to find the resonance frequency and stress distribution. The power generated from the fabricated prototype was found to be 0.25 W using the electromagnetic mechanism and 0.25 mW using the piez...

Flexible active-matrix cells with selectively poled bifunctional polymer-ceramic nanocomposite for pressure and temperature sensing skin

Abstract: A monolithically integrated bifunctional frontplane is introduced to large area electronics. The bifunctional frontplane element is based on a composite foil of piezoelectric ceramic lead titanate nanoparticles embedded in a ferroelectric poly(vinylidene fluoride trifluoroethylene) polymer matrix. Bifunctionality to pressure and temperature changes is achieved by a sequential, area selective two-step poling process, where the polarization directions in the nanoparticles and the ferroelectric polymer are adjusted independently. Thereby, sensor elements that are only piezoelectric or only pyroelectric are achieved. The frontplane foil is overlaid on a thin-film transistor backplane. Our work constitutes a step toward multifunctional frontplanes for large area electronic surfaces.

Acoustic energy harvesting using resonant cavity of a sonic crystal

Abstract: This paper presents the development of an acoustic energy harvester using the sonic crystal and the piezoelectric material. A point defect is created by removing a rod from a perfect sonic crystal. The point defect in the sonic crystal acts as a resonant cavity, and the acoustic waves at the resonant frequency of the cavity can be localized in the cavity. The power generation from acoustic energy is based on the effect of the wave localization in the cavity of the sonic crystal and the direct piezoelectric effect of the piezoelectric material.

Nanoscale characterization of isolated individual type I collagen fibrils: polarization and piezoelectricity

Abstract: Piezoresponse force microscopy was applied to directly study individual type I collagen fibrils with diameters of approximately 100 nm isolated from bovine Achilles tendon. It was revealed that single collagen fibrils behave predominantly as shear piezoelectric materials with a piezoelectric coefficient on the order of 1 pm V(-1), and have unipolar axial polarization throughout their entire length. It was estimated that, under reasonable shear load conditions, the fibrils were capable of generating an electric potential up to tens of millivolts. The result substantiates the nanoscale origin of piezoelectricity in bone and tendons, and implies also the potential importance of the shear load-transfer mechanism, which has been the principle basis of the nanoscale mechanics model of collagen, in mechanoelectric transduction in bone.

Piezoelectric MEMS generators fabricated with an aerosol deposition PZT thin film

Abstract: In this paper, we present the development of two piezoelectric MEMS generators, {3–1} mode and {3–3} mode, which have the ability to scavenge mechanical energy of ambient vibrations and transform it into useful electrical power. These two piezoelectric MEMS generators are of cantilever type made by a silicon process and which can transform mechanical energy into electrical energy through its piezoelectric PZT layers. We developed a PZT deposition machine which uses an aerosol deposition method to fabricate the high-quality PZT thin film efficiently. Our experimental results show that our {3–1} mode device possesses a maximum open circuit output voltage of 2.675 VP-P and a maximum output power of 2.765 µW with 1.792 VP-P output voltage excited at a resonant frequency of 255.9 Hz under a 2.5 g acceleration level. The {3–3} mode device possessed a maximum open circuit output voltage of 4.127 VP-P and a maximum output power of 1.288 µW with 2.292 VP-P output voltage at its resonant frequency of 214 Hz at a 2g acceleration. We also compared the output characteristics of both the {3–1} mode and the {3–3} mode piezoelectric MEMS generators which were both excited at a 2g acceleration level.

Piezoelectric nanoelectromechanical resonators based on aluminum nitride thin films

Abstract: We demonstrate piezoelectrically actuated, electrically tunable nanomechanical resonators based on multilayers containing a 100-nm-thin aluminum nitride (AlN) layer Efficient piezoelectric actuation of very high frequency fundamental flexural modes up to ~80 MHz is demonstrated at room temperature Thermomechanical fluctuations of AlN cantilevers measured by optical interferometry enable calibration of the transduction responsivity and displacement sensitivities of the resonators Measurements and analyses show that the 100 nm AlN layer employed has an excellent piezoelectric coefficient, d_(31)=24 pm/V Doubly clamped AlN beams exhibit significant frequency tuning behavior with applied dc voltage

Piezoelectric-Based Vibration Control: From Macro to Micro/Nano Scale Systems

Abstract: Piezoelectric-Based Vibration-control Systems: Applications in Micro/Nano Sensors and Actuators covers: Fundamental concepts in smart (active) materials including piezoelectric and piezoceramics, magnetostrictive, shape-memory materials, and electro/magneto-rheological fluids; Physical principles and constitutive models of piezoelectric materials; Piezoelectric sensors and actuators; Fundamental concepts in mechanical vibration analysis and control with emphasis on distributed-parameters and vibration-control systems; and Recent advances in piezoelectric-based microelectromechanical and nanoelectromechanical systems design and implementation.

Piezoelectric Ceramics with Super-High Curie Points

Abstract: The perovskite-like layer-structured (PLS) Nd2Ti2O7 and La2Ti2O7 have possibly the highest Curie points of any materials. To pole these ceramics, highly textured, dense ceramics with high DC electrical resistivity are required. The ferroelectric and piezoelectric properties of lead-free Nd2Ti2O7 and La2Ti2O7 grain-oriented ceramics prepared by spark plasma sintering using a two-step method are reported. The Tc of Nd2Ti2O7 and La2Ti2O7 are 1482±5° and 1461±5°C, respectively. The measured piezoelectric constant of the textured La2Ti2O7 was d33=2.6 pC/N. These results now open up the possibility of studying the ferroelectric/piezoelectric properties of the PLS family of ceramics with super-high Curie points.

Vibrations of an elastic structure with shunted piezoelectric patches: efficient finite element formulation and electromechanical coupling coefficients

Abstract: This article is devoted to the numerical simulation of the vibrations of an elastic mechanical structure equipped with several piezoelectric patches, with applications for the control, sensing and reduction of vibrations. At first, a finite element formulation of the coupled electromechanical problem is introduced, whose originality is that provided a set of non-restrictive assumptions, the system's electrical state is fully described by very few global discrete unknowns: only a couple of variables per piezoelectric patches, namely (1) the electric charge contained in the electrodes and (2) the voltage between the electrodes. The main advantages are (1) since the electrical state is fully discretized at the weak formulation step, any standard (elastic only) finite element formulation can be easily modified to include the piezoelectric patches (2) realistic electrical boundary conditions such that equipotentiality on the electrodes and prescribed global charges naturally appear (3) the global charge/voltage variables are intrinsically adapted to include any external electrical circuit into the electromechanical problem and to simulate shunted piezoelectric patches. The second part of the article is devoted to the introduction of a reduced-order model (ROM) of the problem, by means of a modal expansion. This leads to show that the classical efficient electromechanical coupling factors (EEMCF) naturally appear as the main parameters that master the electromechanical coupling in the ROM. Finally, all the above results are applied in the case of a cantilever beam whose vibrations are reduced by means of a resonant shunt. A finite element formulation of this problem is described. It enables to compute the system EEMCF as well as its frequency response, which are compared with experimental results, showing an excellent agreement.

Piezoelectric aluminum nitride nanoelectromechanical actuators

Abstract: This letter reports the implementation of ultrathin (100 nm) aluminum nitride (AlN) piezoelectric layers for the fabrication of vertically deflecting nanoactuators. The films exhibit an average piezoelectric coefficient (d31∼−1.9 pC/N), which is comparable to its microscale counterpart. This allows vertical deflections as large as 40 nm from 18 μm long and 350 nm thick multilayer cantilever bimorph beams with 2 V actuation. Furthermore, in-plane stress and stress gradients have been simultaneously controlled. The films exhibit leakage currents lower than 2 nA/cm2 at 1 V, and have an average relative dielectric constant of approximately 9.2 (as in thicker films). These material characteristics and actuation results make the AlN nanofilms ideal candidates for the realization of nanoelectromechanical switches for low power logic applications.

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

Abstract: We describe the concept, the fabrication, and the most relevant properties of a piezoelectric-polymer system: Two fluoroethylenepropylene (FEP) films with good electret properties are laminated around a specifically designed and prepared polytetrafluoroethylene (PTFE) template at 300 °C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. For electric charging, the two-layer FEP system is subjected to a high electric field. The resulting dielectric barrier discharges inside the tubular channels yield a ferroelectret with high piezoelectricity. d33 coefficients of up to 160 pC/N have already been achieved on the ferroelectret films. After charging at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130 °C. Advantages of the transducer films include ease of fabrication at laboratory or industrial scales, a wide range of possible geometrical and processing parameters, straightforward control of the uniformity of the polymer ...

Piezoelectric potential gated field-effect transistor based on a free-standing ZnO wire.

Abstract: We report an external force triggered field-effect transistor based on a free-standing piezoelectric fine wire (PFW). The device consists of an Ag source electrode and an Au drain electrode at two ends of a ZnO PFW, which were separated by an insulating polydimethylsiloxane (PDMS) thin layer. The working principle of the sensor is proposed based on the piezoelectric potential gating effect. Once subjected to a mechanical impact, the bent ZnO PFW cantilever creates a piezoelectric potential distribution across it width at its root and simultaneously produces a local reverse depletion layer with much higher donor concentration than normal, which can dramatically change the current flowing from the source electrode to drain electrode when the device is under a fixed voltage bias. Due to the free-standing structure of the sensor device, it has a prompt response time less than 20 ms and quite high and stable sensitivity of 2%/μN. The effect from contact resistance has been ruled out.

Enhanced piezoelectric and ferroelectric properties in Mn-doped Na0.5Bi0.5TiO3-BaTiO3 single crystals

Abstract: High piezoelectric and ferroelectric properties have been found in Mn-doped Na0.5Bi0.5TiO3–BaTiO3 single crystals, which were grown by a top-seeded solution method. The electrical resistivity, dielectric constant, and ferroelectric and piezoelectric properties were all found to be notably enhanced by Mn. The piezoelectric constant d33 and electromechanical coupling coefficients kt and k31 were found to be as high as 483 pC/N, 0.56, and 0.40, respectively. These values are much higher than those previously reported for Pb-free piezoelectric crystals, demonstrating the real potential for alternative lead-free systems for sensor and piezoelectric applications.

High-Performance Piezoelectric Single Crystals of Complex Perovskite Solid Solutions

Abstract: Relaxor-based single crystals of complex perovskite solid solutions, Pb(Mg1/3Nb2/3)O3–PbTiO3 [PMN–PT] and Pb(Zn1/3Nb2/3)O3–PbTiO3 [PZN–PT], exhibit extraordinary piezoelectric performance, with extremely high piezoelectric coefficients, very large electromechanical coupling factors, and exceptionally high strain levels. These materials outperform the currently used Pb(Zr1–xTix)O3 [PZT] ceramics, making them the materials of choice for the next generation of electromechanical transducers for a broad range of advanced applications. In this article, recent major advances in the development of piezocrystals are reviewed in terms of crystal growth, piezoelectric properties, crystal chemistry, domain structure, and device applications.

Electromechanical Modeling of Piezoelectric Energy Harvesters

Abstract: Vibration-based energy harvesting has been investigated by several researchers over the last decade. The ultimate goal in this research field is to power small electronic components (such as wireless sensors) by using the vibration energy available in their environment. Among the basic transduction mechanisms that can be used for vibration-to-electricity conversion, piezoelectric transduction has received the most attention in the literature. Piezoelectric materials are preferred in energy harvesting due to their large power densities and ease of application. Typically, piezoelectric energy harvesters are cantilevered structures with piezoceramic layers that generate alternating voltage output due to base excitation. This work presents distributed-parameter electromechanical models that can accurately predict the coupled dynamics of piezoelectric energy harvesters. First the issues in the existing models are addressed and the lumped-parameter electromechanical formulation is corrected by introducing a dimensionless correction factor derived from the electromechanically uncoupled distributed-parameter solution. Then the electromechanically coupled closed-form analytical solution is obtained based on the thin-beam theory since piezoelectric energy harvesters are typically thin structures. The multi-mode electromechanical frequency response expressions obtained from the analytical solution are reduced to single-mode expressions for modal vibrations. The analytical solutions for the electromechanically coupled voltage response and vibration response are validated experimentally for various cases. The single-mode analytical equations are then used for deriving closed-form relations for parameter identification and optimization. Asymptotic analyses of the electromechanical frequency response functions are given along with expressions for the short-circuit and the open-circuit resonance frequencies. A simple experimental technique is presented to identify the optimum load resistance using only a single resistor and an open-circuit voltage measurement. A case study is given to compare the power generation performances of

Connected Vibrating Piezoelectric Bimorph Beams as a Wide-band Piezoelectric Power Harvester

Abstract: We analyze coupled flexural vibration of two elastically and electrically connected piezoelectric beams near resonance for converting mechanical vibration energy to electrical energy. Each beam is a so-called piezoelectric bimorph with two layers of piezoelectrics. The 1D equations for bending of piezoelectric beams are used for a theoretical analysis. An exact analytical solution to the beam equations is obtained. Numerical results based on the solution show that the two resonances of individual beams can be tuned as close as desired by design when they are connected to yield a wide-band electrical output. Therefore, the structure can be used as a wide-band piezoelectric power harvester.

Polymorphic phase transition and excellent piezoelectric performance of (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 lead-free ceramics

Abstract: A lead-free ceramic with the composition (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d33=262 pC/N, kp=0.53, k33=0.63, and k31=0.31 with e′=1290 and tan δ=0.019 at room temperature. In spite of the orthorhombic-tetragonal polymorphic phase transition around 30 °C, temperature stability of the electromechanical coupling coefficients is very good over the common usage temperature interval between −40 and 85 °C. Furthermore, the piezoelectric properties remain almost unchanged in the severe thermal aging test down to −150 °C and up to about 300 °C. It is suggested that the outstanding piezoelectric performance of this ceramic can be largely ascribed to the phase coexistence in a wide temperature range and the Ta-rich composition.

Phase Transition Temperatures and Piezoelectric Properties of (Bi 1/2 Na 1/2 )TiO 3 -and (Bi 1/2 K 1/2 )TiO 3 -Based Bismuth Perovskite Lead-Free Ferroelectric Ceramics

Abstract: The phase transition temperatures and the dielectric, ferroelectric, and piezoelectric properties of bismuth perovskite lead-free ferroelectric ceramics such as (Bi1/2Na1/2)TiO3 (BNT)- and (Bi1/2Na1/2)TiO3 (BKT)-based solid solutions have been reviewed According to the results obtained by our group, these ceramics can be considered as superior lead-free piezoelectric materials for reducing environmental damage Perovskite-type ceramics appear to be suitable for actuator and high-power applications that require a large piezoelectric constant d33 and a high Curie temperature TC or a high depolarization temperature Td (> 200degC) In this paper, we summarize the relationship between phase transition temperatures and piezoelectric properties In the case of the BNT-based solid solutions, the highest piezoelectric properties were obtained at the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases However, d33 and Td were shown to have a tradeoff relationship Considering the high Td and high d33, the tetragonal side of the MPB composition is suitable for piezoelectric actuator application Meanwhile, the Qm values on the rhombohedral side of the MPB composition were better than those on the tetragonal side, and excellent high-power characteristics were obtained for Mn-doped BNT-(Bi1/2Na1/2)TiO3-BKT ternary systems with rhombohedral symmetry BKT ceramics were prepared by the hot-pressing (HP) method, and their ferroelectric and piezoelectric properties were clarified BKT ceramics doped with a small amount of Bi have a relatively high remanent polarization of Pr = 276 muC/cm2 and high piezoelectric properties (k33 = 040 and d33 = 101 pC/N) In addition, it was clarified that BKT ceramics have a high Td of approximately 300degC The solid solution (1-x)BKT-xBaTiO3 (BKT-BT100x) exhibited a high Td of approximately 300degC at x > 04

Characterization of Hard Piezoelectric Lead-Free Ceramics

Abstract: K4CuNb8O23 doped K0.45Na0.55NbO3 (KNN-KCN) ferroelectric ceramics were found to exhibit asymmetrical polarization hysteresis loops, related to the development of an internal bias field. The internal bias field is believed to be the result of defect dipoles of acceptor ions and oxygen vacancies, which lead to piezoelectric "hardening" effect, by stabilizing and pinning of the domain wall motion. The dielectric loss for the hard lead-free piezoelectric ceramic was found to be 0.6%, with mechanical quality factors Q on the order of >1500. Furthermore, the piezoelectric properties were found to decrease and the coercive field increased, when compared with the undoped material, exhibiting a typical characteristic of "hard" behavior. The temperature usage range was limited by the polymorphic phase transition temperature, being 188degC. The full set of material constants was determined for the KNN-KCN materials. Compared with conventional hard PZT ceramics, the lead-free possessed lower dielectric and piezoelectric properties; however, comparable values of mechanical Q, dielectric loss, and coercive fields were obtained, making acceptor modified KNN based lead-free piezoelectric material promising for high-power applications, where leadfree materials are desirable.

Method for operating a piezoelectric element

Abstract: The invention relates to a method for operating a piezoelectric element, wherein a first voltage (1) is applied to a piezoelectric element, said voltage effecting a first deflection by a travel (w) of the piezoelectric element, and an electric discharge of the piezoelectric element after application of the first voltage effecting a first contraction of the piezoelectric element by a first compression (x). After the first contraction, a second voltage (2) is applied to the piezoelectric element, said voltage having an opposite polarity relative to the first voltage (1) and effecting a further contraction of the piezoelectric element by a second compression (y). A repeated application of the first voltage (1) after the electric discharge of the applied second voltage (2) effects a deflection of the piezoelectric element by the same travel (w).

Electromechanical properties of A-site (LiCe)-modified sodium bismuth titanate (Na0.5Bi4.5Ti4O15) piezoelectric ceramics at elevated temperature

Abstract: The Aurivillius-type bismuth layer-structured (NaBi)0.46(LiCe)0.04Bi4Ti4O15 (NBT-LiCe) piezoelectric ceramics were synthesized using conventional solid-state processing. Phase analysis was performed by x-ray diffraction and microstructural morphology was assessed by scanning electron microscopy. The dielectric, piezoelectric, ferroelectric, and electromechanical properties of NBT-LiCe ceramics were investigated. The piezoelectric activities were found to be significantly enhanced compared to NBT ceramics, which can be attributed to the lattice distortion and the presence of bismuth vacancies. The dielectric and electromechanical properties of NBT-LiCe ceramics at elevated temperature were investigated in detail. The excellent piezoelectric, dielectric, and electromechanical properties, coupled with high Curie temperature (Tc=660 °C), demonstrated that the NBT-LiCe ceramics are the promising candidates for high temperature applications.