Electrostrictive Ceramics Research Articles

Ultrahigh strain and piezoelectric behavior in relaxor based ferroelectric single crystals

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3–PbTiO3 and Pb(Mg1/3Nb2/3)O3–PbTiO3 were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3, morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33’s)>2500 pC/N and subsequent strain levels up to >0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for 〈001〉 oriented rhombohedral crystals, although 〈111〉 is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics, could be achieved being related to an E-field induced phase transformation. High electromechanical coupling (k33)>90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

Multilayered digital actuator composed of electrostrictive ceramics

In order to depress the hysteresis phenomenon of a digital actuator which is coded with driven numbers of piezoelectric ceramics, a new actuator composed of electrostrictive ceramics of PMW-PNN-PT family has been investigated. The experimental results have indicated that the actuator works well from the viewpoint of the hysteresis property but showed degraded temperature characteristics. Therefore, a new method to compensate the characteristics has further been investigated by combining two ceramics of different temperature coefficient and found that the average temperature coefficient of displacement in the temperature range from 15 to 30°C has been reduced from 1.13 to 0.26%/°C or less. The observed temperature dependence of displacements is in essential agreement with the simulated curve which takes account of the effect of spontaneous polarization of the electrostrictive ceramics.

Relaxor based ferroelectric single crystals for electro-mechanical actuators

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3- PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr, Ti)O3 (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33’s) >2200 pC/N and subsequent strain levels up to >0.5% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, possibly being related to an E-field induced phase transformation. High electromechanical coupling (k33) >90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

Two-dimensional modeling and characterization of PMN electrostrictive materials using the finite-element code ATILA

New electrostrictive lead magnesium niobate ceramics (PMN) are promising materials for applications in the field of actuators, transducers, and motors. These materials have strains roughly an order of magnitude larger than those of the lead zirconate–titanate (PZT) ceramics. However, the use of these electrostrictive materials for practical applications presents some difficulties: highly nonlinear properties, temperature dependence of dielectric permittivity near the dielectric maximum, dc bias field needed. To improve the use of these electrostrictive materials, a better knowledge of the physical tensors of PMN and the development of a numerical tool are necessary. In this study, the development of a two-dimensional electrostrictive element in the ATILA code for nonlinear static analysis and time-domain analysis is presented. Two different models are tested including or not the effect of polarization saturation. The validity of both models is demonstrated by comparing computed strain and charge density with analytical solutions and measured results for a PMN bar at various electric dc fields and mechanical prestresses. Measurements are realized to obtain the complete physical tensor of PMN. Finally, the model is applied to a Janus transducer to describe the application of prestress and the electrical dc polarization.

A transduction model of lead magnesium niobate‐titanate

Lead magnesium niobate (PMN) and lead magnesium niobate–lead titanate (PMNPT) are electrostrictive ceramics that exhibit high strains when a sample is subjected to a high voltage. The strain as a function of voltage is an almost perfect square‐law over a large range of voltages, neglecting saturation and hysteresis. Unlike piezoelectric ceramics, these materials will not accept a significant permanent polarization, so the behavior cannot be linearized in this way. A transduction model of these materials based on an analogy to the Hunt electrostatic transducer is presented. The Hunt model is generalized for radiation loading and for a passive dielectric material between the plates. The dielectric model includes saturation but excludes hysteresis. The model is inverted analytically to determine a driving‐voltage waveform which permits a PMN(PT)‐based transducer to be driven at high voltage in a harmonic‐ and transient‐free manner. Successful experimental applications of the model to measurements obtained from PMN(PT) samples are presented. The results include a description of a successful attempt to drive a PMN(PT) sample in a harmonic‐ and transient‐suppressed manner at high voltage.

Intelligent Ceramic Materials: Issues of Brittle Fracture

In this paper we review the brittle fracture behavior of piezoelectric and electrostrictive ceramics of interest for intelligent material systems. Properties of importance, such as critical fracture toughness, strength, and susceptibility to moisture enhanced crack growth, are addressed, especially as they are affected by the material's microstructure and chemistry. Local strains and ferroelectric domains produced by phase transformations in these materials are shown to have a direct influence on both fracture toughness and strength. The cyclic stressing of a piezoelectric ceramic is discussed in terms of the structural damage produced by this mode of loading. Finally, tradeoffs in improved reliability, which may be achievable through suitable variations in composition or microstructure, are compared against possible losses in the piezoelectric properties of interest.

Electrostrictive actuators on base of PMN-PSN solid solution ceramics

A set of actuators has been made using 0.55PbMg1/3Nb2/3O3-0.45PbSc1/2Nb1/2O3 electrostrictive ceramics. Static and dynamic properties of these actuators are presented.

High-field electromechanical properties of some Pb(Mg1/3Nb2/3)O3-PbTiO3-based relaxors

Abstract Electrostrictive ceramics in the (1–x)[(1–y)Pb(Mg1/3Nb2/3)O3-yPbTiO3]-xMeTiO3 system, where Me is Sr or Ba, have discriminating properties for a variety of electromechanical applications. Electrostrictors fill niches that depend on a large mechanical energy density (24 kJ/m3), large ( 600 pC/N) effective d33, and low electromechanical hysteresis (<2%). As relaxor ceramics, the weak-field material behavior is dependent on both temperature and frequency. Two groups of materials with differing microstructures were examined to assess the relaxor nature of the high-field electromechanical properties. Both weak and high-field measurements were used to clarify the transition behavior and assess the engineering utility of the two material types. Although these two groups of materials were synthesized from identical starting materials, major differences were obtained in terms of grain size, relative permittivity, dielectric aging, and strain and average hysteresis.

Development of piezoelectric composites for transducers

For the past decade and a half, many different types of piezoelectric ceramic-polymer composites have been developed intended for transducer applications. These diphasic composites are prepared from non-active polymer, such as epoxy, and piezoelectric ceramic, such as PZT, in the form of filler powders, elongated fibers, multilayer and more complex three-dimensional structures. For the last four years, most of the efforts have been given to producing large area and fine scale PZT fiber composites. In this paper, processing of piezoelectric ceramic-polymer composites with various connectivity patterns are reviewed. Development of fine scale piezoelectric composites by lost mold, injection molding and the relic method are described. Research activities of different groups for preparing large area piezocomposites for hydrophone and actuator applications are briefly reviewed. Initial development of electrostrictive ceramics and composites are also

Calculation of quasi-static electromechanical coupling coefficients for electrostrictive ceramic materials

The quasi-static coupling coefficients, k/sub 13/ and k/sub 33/, for electrostrictive ceramics are computed analytically. The calculation is based on a three-dimensional constitutive relation that models both electrostriction and nonlinear dielectric behaviors. The results show that the coupling factors depend on the amplitudes of the applied ac field and the dc bias, as well as the mechanical prestress. For an actuator without bias voltage or prestress, the coupling coefficients approach an asymptotic value with increasing electric field. The primary coefficients, k/sub 13/ and k/sub 33/, for a lead magnesium niobate, Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/BaTiO/sub 3/(PMN-PT-BT), based relaxor ferroelectric are computed as an example. The results show that the coupling coefficients for PMN-PT-BT materials are roughly comparable with those of existing piezoelectrics. These coefficients are important parameters for material section and power source design for transducer devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mixing and detection of microwave signals in fibre-opticelectrostrictive sensor

The nonlinear strain–polarisation relationship in electrostrictive ceramics is exploited to demonstrate, for the first time, detection and mixing of microwave signals in a fibre-optic electrostrictive sensor. The nonlinear electrostrictive transducer mixes the microwave signal with a signal from a local oscillator, and the resulting strain at the intermediate frequency is detected with a fibre-optic interferometer. The sensor demonstrated approximately flat response in the microwave regime (up to 20 GHz) with a resolution of 5 × 10-6 V/√Hz.

Observation of residual strain in dynamically excited electrostrictors

We measured the dynamic small strain effects in electrostrictive ceramics with a high resolution fiber optic interferometer. The dynamic strain response of both a lead magnesium niobate (PMN) and a lead zirconate titanate (PZT)-based electrostrictive ceramic exhibited a residual signal which cannot be understood by the simple scalar strain-polarization relationship, e+QP2. The magnitude of the residual signal decreased as a function of increasing temperature indicating that the residual strain signal has origins in the remnant electric polarization of the material. The magnitude of the residual strain was generally higher for the PZT-based electrostrictor than for the PMN based sample. The observed residual strain signal represents a novel phenomenon previously unseen in the dynamical strain response of electrostrictive ceramics.

Electrostrictive ceramics for underwater transducer applications

The electromechanical properties of two electrostrictive materials designed for use in underwater acoustic applications are determined as functions of temperature and electric field. The materials are 0.859 Pb(Mg1/3Nb2/3)O3–0.141 PbTiO3 doped with 2.5% SrTiO3 or BaTiO3. Dielectric properties are determined as functions of temperature and electric field. The equivalent piezoelectric coefficients were found as functions of temperature to be equal to or superior to the lead zirconate–titanate ceramics at very modest dc bias fields (2 kV/cm) at temperatures in the range from 10 to 35 °C. Outside of this temperature range, the piezoelectric and dielectric coefficents decrease rapidly. Electromechanical losses were found to be sufficiently small for the SrTiO3 composition but not the BaTiO3 composition.

High resolution fiber-optic voltage sensors based on the electrostrictive effect

Abstract We demonstrate high resolution fiber-optic dc and ac voltage sensors based on the electrostrictive effect in PMN based relaxor ferroelectrics. The quadratic relationship between the applied voltage and the induced strain in electrostrictive ceramics allows mixing of a signal at frequency ω with a carrier at a much higher frequency ω, thereby upconverting the information of interest to a frequency region (ω±ω) in which 1/f noise is not significant. Using PMN based electrostrictive elliptical transducers in conjunction with high resolution fiber optic interferometers we have observed a resolution of 129 nV/√Hz at 30 milliHertz and 40 nV/√Hz at 1 Hz. The device functions as an ac voltage sensor in the de-biased mode. We have observed resolution of < 10 nV/√Hz between 500 Hz -50 kHz when the device is used in the dc-biased mode.

Stresses Near the End of an Internal Electrode in Multilayer Electrostrictive Ceramic Actuators

AbstractStresses near the end of an internal electrode in a multilayer electrostrictive ceramic actuator are studied in detail. A finite element program capable of overcoming two major difficulties is developed. The program solves both the mechanical and electrical coupling problem and the nonlinear electric field and electric displacement relationship for these materials. Results indicate that the stress difference between the coupled and the uncoupled cases can only be distinguished when a stress singularity is present. Tensile stresses are found both in front, and behind, the end of an internal electrode. The magnitude of the stresses is predetermined by the material constants.

Development of electrostrictive ceramic compositions for high‐power sonar transducers

New emphasis on active sonar applications requires the development of compact, high‐power sonar projectors. For low‐frequency use, one desires to be able to drive the transducer elements at high electric field levels in order to achieve large strains. The conventional lead–zirconate–titanate (PZT) ceramics have been widely used for the design and fabrication of sonar projectors, but these ceramics suffer the shortcomings of strain limitation and nonlinear properties under high drive. In recent years, the Navy has been developing new electrostrictive ceramics of the lead–magnesium–niobate family, because these electrostrictive ceramics can produce much greater strains than the PZTs. In particular, a new class of lead–magnesium–niobate lead–titanate (commonly called PMN–PT) solid solution compositions has been found to offer the combined advantages of high‐strain, low‐dielectric, and hysteresis losses. The development of these materials is summarized, and the test results from prototype transducers fabricated using the new electrostrictive PMN–PTs are also presented. [Work supported by ONR/T.]

Electromechanical properties of new electrostrictive materials for underwater acoustical applications

Electrostrictive ceramics are known to be capable of generating strains that far exceed those of conventional piezoelectric lead–zirconate–titanate (PZT) ceramics. Several lead–magnesium–niobate (PMN) compositions developed earlier were useful only at higher temperatures than those of interest to the sonar community. A new barium‐modified PMN–PT ceramic is described. This material can operate at lower temperatures and has very low losses, making it a prime candidate for high‐power sonar transducer applications. Another family of electrostrictive materials capable of generating large strains is lanthanum‐modified PZT (or PLZT). These materials exhibit strains up to 0.1% along with extremely high dielectric strength, but their hysteresis losses are higher than those of PMN or PMN–PT ceramics. Since the maximum possible strain output is usually the important parameter in actuator applications, the PLZT family may have potential for new actuator designs. Strain measurements for these new electrostrictive cera...

Temperature-stable high electrostrictive strain relaxer ferroelectric ceramics for servo-actuator applications

For servo-type actuator applications, temperature-stable high electric-field-induced-strain electrostrictive lead magnesium niobate (PMN)-based relaxer ferroelectric materials are needed. The synthesis technique of the PMN-based composition with 100% perovskite phase is described. The effects of dopants and processing technology on the dielectric properties and electrostrictive properties are discussed in detail.

SmC5: Hydrothermally processed piezoelectric and electrostrictive ceramics

Abstract Lead titanate and lead magnesium niobate ceramics are fabricated from powders prepared by hydrothermal synthesis. The results of powder and ceramic characterisation are presented and compared with similar data obtained for ceramics fabrication by conventional mixed oxides.

Electrostrictive and Piezoelectric Materials for Actuator Applications

The piezoelectric and electrostrictive effects in ferroelectric ceramics are reviewed with an emphasis on those properties that are relevant for applications in actua tors. Various contributions to the piezoelectric effect in ferroelectric ceramics, especially lead zirconate titanate ceramics, are discussed in some detail. Relaxor ferroelectrics such as lead magnesium niobate are shown to be a unique family of materials with very attrac tive electrostrictive effects as well as piezoelectric properties. Finally, several actuator sys tems that employ piezoelectric end electrostrictive ceramics are briefly discussed.