Soft Lead Zirconate Titanate Research Articles

Temperature- and dc bias field- dependent piezoelectric effect of soft and hard lead zirconate titanate ceramics

The dc bias field-dependent piezoelectric coefficient d 33 of lead zirconate titanate ceramics (PZT5, PZT8 and P5H) were determined by a quasi-static method. It was found that piezoelectric coefficient d 33 was almost independent of positive dc bias field for PZT8 and PZT5 ceramics, while for P5H ceramic an obvious decrease of coefficient d 33 was observed under positive dc bias field. On the other hand, the temperature-dependent piezoelectric response for PZT ceramics were investigated by both quasi-static and resonance methods. The piezoelectric coefficient d 33 was found to increase with increasing temperature for both PZT5 and PZT8 ceramics. For P5H ceramics, coefficient d 33 showed a first decreasing and then increasing tendency with respect to temperature. These results were discussed in terms of intrinsic and extrinsic contributions to piezoelectric response.

Self-heat generation in piezoelectric stack actuators used in fuel injectors

Multilayer piezoelectric actuators are used in fuel injectors due to their quick response,high efficiency, accuracy, low power consumption, and excellent repeatability. Experimentalresults for soft lead zirconate titanate (PZT) stack actuators have shown that a significantamount of heat is generated when they are driven under high frequency and/or highelectric-field magnitudes, both of which occur in fuel injectors. Self-heat generation in theseactuators, mainly caused by losses, can significantly affect their reliability and piezoelectricproperties, and may also limit their application. Other studies have demonstrated that atlarge unipolar electric-field magnitudes, displacement–electric-field loss (displacementhysteresis) shows a direct relation with polarization–electric-field loss (dielectrichysteresis). In this paper, a simplified analytical self-heating model is presented.The model directly relates self-heating in multilayer piezoelectric actuators todisplacement–electric-field loss (displacement hysteresis). The model developed isbased on the first law of thermodynamics, and accounts for different parameterssuch as geometry, magnitude and frequency of applied electric field, duty cyclepercentage, fuel type, and environmental properties. The model shows reasonableagreement with experimental results at low and high electric-field magnitudes.

A Note on Tensile Testing of Poled and Unpoled Piezoelectric Ceramics

Abstract: Tensile tests were carried out on unpoled and poled soft lead zirconate titanate (PZT) ceramic materials: APC #855 (APC International) and PZT‐5H (Morgan Electro Ceramics). The tests were performed on a dog‐bone specimen with holes at its edges. A methodology is presented for carrying out these tests. A tensile stress was applied by means of Kevlar strings through the specimen holes. The poling direction was perpendicular to the longitudinal specimen axis. For the poled specimens, two electrical boundary conditions were applied, namely, E = 0 and D = 0. Strains were measured at four points on the sample. For each specimen, the bending percentage was calculated. For all specimens, stress–strain curves were found to be initially linear; at a strain of approximately 0.0001, the curves became nonlinear. Young’s modulus was measured in the linear region of the stress–strain curve. Young’s modulus values were highest for the poled material with an open circuit boundary condition (D = 0) and lowest for the unpoled material.

Influence of extrinsic contribution on the macroscopic properties of hard and soft lead zirconate titanate ceramics

In this work, the contribution of the extrinsic effect to the macroscopic properties in soft and hard lead zirconate titanate ceramics is directly evaluated. Close to the room temperature, poled hard ceramics show an anomalous behavior, which is notably different from that of soft ceramics, not only in dielectric but also in piezoelectric and elastic responses. Hence, at room temperature their properties are thermally stable and the losses are unusually low. It is suggested that two mechanisms are present, with one mechanism inhibiting the other.

Stress dependence and scaling of subcoercive field dynamic hysteresis in 0.5Pb(Zr1/2Ti1/2)O3–0.5Pb(Zn1/3Nb2/3)O3 ceramic

Stress dependence and scaling behavior of subcoercive field dynamic ferroelectric hysteresis were investigated in rhombohedral 0.5Pb(Zr1/2Ti1/2)O3–0.5Pb(Zn1/3Nb2/3)O3 (0.5PZT–0.5PZN) bulk ceramic with profound relaxor characteristics. The scaling relation of hysteresis area ⟨A⟩ against frequency f, field amplitude E0, and stress σ for the minor loops takes a form of ⟨A−Aσ=0⟩∝f−0.34E03.68σ0.35, which is very similar to that of soft and hard lead zirconate titanate ceramics with the same disrupted domains. This study suggests that the domain structures play a significant role in controlling the dynamic hysteresis behavior of ferroelectric materials.

Thermo-electro-mechanical Performance of Piezoelectric Stack Actuators for Fuel Injector Applications

Piezoelectric actuators are increasingly used in fuel injectors due to their quick response, high efficiency, accuracy, and excellent repeatability. Current understanding of their thermo-electro-mechanical performance under dynamic driving conditions appropriate for fuel injection is, however, limited. In this paper, the thermo-electro-mechanical performance of soft Lead Zirconate Titanate (PZT) stack actuators is experimentally investigated over a temperature range of -30°C to 80°C, under driving electric fields of up to 2.0 kV/mm (using an AC drive method and a biased DC offset), different frequencies, and a constant preload of about 5 MPa. Experimental results show that the dynamic stroke of the actuators increases with the magnitude and frequency of the applied electric field, as well as ambient temperature. The dynamic stroke was also found to increase with decreased driving field rise time, which is equivalent to increasing the driving field frequency. At driving frequencies lower than the resonance frequency of the test apparatus (~500 Hz), the strain-electric field behavior under different temperatures agreed well with previously obtained quasi-static results. The duty cycle was found to have a minimal effect on dynamic stroke but significantly affected the amount of heat generated under high electric field magnitudes and/or frequencies. The temperature increase due to self-heat generation under a continuous AC driving field (100% duty cycle) was very high, and limited the maximum driving field magnitude and/or frequency. Reducing the duty cycle significantly decreased the amount of heat generation.

Thermal activation of ferroelectric switching

By applying the theory of thermally activated nucleation to the switching of ferroelectric domains, a method is developed to experimentally obtain the value of both the activation enthalpy, ΔH, and activation volume, V*, for the thermally activated process involved in ferroelectric switching. The method was applied to the switching of a soft lead zirconate titanate and values of ΔH=(0.16±0.02) eV and V*=(1.62±0.16)×10−25 m3 were obtained at the coercive field. These values imply that the energy, ΔU, required for the formation of switching nuclei is mainly supplied by the work done by the electric field. A comparison of these values with those obtained from theoretical considerations suggests that the switching is achieved by the sideways expansion of nuclei formed at the domain boundaries in the form of low amplitude and long wavelength fluctuations of the domain walls.

Pyroelectricity versus conductivity in soft lead zirconate titanate (PZT) ceramics

The electrical behavior of modified soft lead zirconate titanate (PZT) ceramics has been studied as a function of temperature at different direct current (dc) electric fields and grain sizes. As ferroelectrics, such as PZT, are highly polarizable materials, poling, depolarization, and electric conduction contribute to the total electrical current, which leads to anomalous electrical behavior as a function of temperature. The PZT appeared to have a high pyroelectric coefficient, and it was found that the displacement current hides the conduction current near room temperature. The (long-time) steady-state electrical resistivity of the soft PZT used has a typical, relatively high value of 3.6 × 1012 Ω·cm near room temperature. The resistivity above the Curie temperature was two orders of magnitude lower than the room temperature. The resistivity decreases with increasing grain size probably due to the increased Pb vacancy concentration resulting as a consequence of a higher sintering temperature. The values of activation energies suggest that the charge carriers at high temperature are mainly oxygen vacancies. At intermediate temperature, the electrical behavior is controlled by the counteracting effect of depolarization and conduction. Considering the pyroelectric effect and the conduction, it was thus possible to explain the electrical behavior of this soft PZT ceramic over the temperature range considered.

Stress- and temperature-dependent scaling behavior of dynamic hysteresis in soft PZT bulk ceramics

Effects of electric field-frequency, electric field-amplitude, mechanical stress, and temperature on the hysteresis area, especially the scaling form, were investigated in soft lead zirconate titanate (PZT) bulk ceramics. The hysteresis area was found to depend on the frequency and field-amplitude with the same set of exponents as the power-law scaling for both with and without stresses. The inclusion of stresses into the power-law was obtained in the form of which indicates the difference in energy dissipation between the under-stress and stress-free conditions. The power-law temperature scaling relations were obtained for hysteresis area ⟨A⟩ and remanent polarization Pr, while the coercivity EC was found to scale linearly with temperature T. The three temperature scaling relations were also field-dependent. At fixed field amplitude E0, the scaling relations take the forms of , Pr ∝T−1.2322 and (EC0 - EC) ∝T.

Grain size effect on the switching current in soft ferroelectric lead zirconate titanate

Recently, we reported on the appearance of a double peak in the switching current during the reverse poling. In the present paper, the switching current measurements have been carried out on a soft lead zirconate titanate as a function of grain size. While in small grains only a small single switching peak is observed, large grains, however, showed double peak switching, as commonly observed in this material. The pyroelectric coefficient curves show a consistent trend with the switching curves. This behavior is attributed to non-180° domain switching during the reversed poling case as a result of residual stresses developed during forward poling.

Advances in the characterisation of domain switching in ferroelectric ceramics

In ferroelectric materials, extrinsic contributions such as domain wall vibrations, domain switching, and interphase boundary motion contribute to fatigue and aging, nonlinearity, and hysteresis in the piezoelectric response. It also affects the deformation behaviour, and influences the fracture mechanics. The most prevalent extrinsic contribution is ferroelectric/ferroelastic domain switching. Recent advances in diffraction techniques offer many opportunities for novel characterisation of domain switching and its influence on macroscopic properties. This paper presents the results of two such techniques which have been used to characterise extrinsic mechanisms in situ in a soft lead zirconate titanate (PZT) ceramic. In the first example, stroboscopic, time-resolved neutron diffraction is used to represent the ferroelectric/ferroelastic domain switching during a single cycle of a 1 kHz unipolar electric field with a magnitude of half of the coercive field. In the second example, highenergy X-ray microdiffraction is used to measure the spatial distribution of ferroelastic domain switching around a crack tip in transmission geometry under an applied stress intensity factor of KI=0.71 MPa•m. Introduction Ferroelectric ceramics are used in a wide variety of electromechanical devices including sonar, ultrasound, sensors and actuators, non-volatile memories, and micro-electromechanical systems (MEMS). In ferroelectric ceramics, changes in the ferroelectric/ferroelastic domain structures can affect the measurable bulk properties in an advantageous or disadvantageous manner. For example, domain wall motion during dynamic actuation increases the electric-field-induced strain but also contributes to nonlinearity, hysteresis, and fatigue [1]. Domain switching also contributes to fracture toughness enhancement in ferroelectric/ferroelastic ceramics, which is expressed both as an increase in the initiation toughness as well as a rising R-curve behaviour. It is therefore important to characterise such mechanisms in order to reveal their exact role in these and other cases. 442 European Powder Diffraction Conference, EPDIC 10 A schematic diagram of the process of domain switching is shown in figure 1. As shown, the application of an electric field or stress along particular directions of a bulk ceramic sample leads to a change in the volume fraction of domain types present within individual grains. Domain structures have been characterised using diffraction for decades [2]. The essence of such measurements is the relationship between the diffracted intensity of particular Bragg peaks and the volume fraction of ferroelectric/ferroelastic domains present within the sample. The simplest representation (i.e., for a sample with tetragonal symmetry) of the changes in the diffraction pattern is shown in figure 1(c).

Double-peak switching current in soft ferroelectric lead zirconate titanate

Switching current measurements have been carried out on a soft lead zirconate titanate (PXE52, donor doped, modified proprietary composition with the overall formula PbZr0.415Ti0.585O3). The experiments showed a single switching current peak during the application of electric field to a nonpoled (virgin) sample. However, an unusual double peak for the switching current was observed upon reversing the electric field polarity. The pyrocurrent for a forward and reverse poled sample showed a related behavior. A single pyropeak is observed in the forward poled case and broadened peak was observed in case of a reverse poled sample. This behavior is attributed to non-180° domain switching during the reverse poled case as a result of residual stresses developed during the forward poling.

Crack tip process zone domain switching in a soft lead zirconate titanate ceramic

Non-180° domain switching leads to fracture toughness enhancement in ferroelastic materials. Using a high-energy synchrotron X-ray source and a two-dimensional detector in transmission geometry, non-180° domain switching and crystallographic lattice strains were measured in situ around a crack tip in a soft tetragonal lead zirconate titanate ceramic. At K I = 0.71 MPa m 1/2 and below the initiation toughness, the process zone size, spatial distribution of preferred domain orientations, and lattice strains near the crack tip are a strong function of direction within the plane of the compact tension specimen. Deviatoric stresses and strains calculated using a finite element model and projected to the same directions measured in diffraction correlate with the measured spatial distributions and directional dependencies. Some preferred orientations remain in the crack wake after the crack has propagated; within the crack wake, the tetragonal 0 0 1 axis has a preferred orientation both perpendicular to the crack face and toward the crack front.

Displacement amplification and electric characteristics of modified rectangular cymbal transducers using electroactive materials

Three typical electroactive materials were used as the drive elements for a cymbal transducer. The included materials were hard and soft lead zirconate titanate (PZT) piezoelectric ceramics and single crystal lead magnesium niobate–lead titanate (PMNT). Finite element analysis was used to calculate the displacement of the transducer under dc voltage. The displacement of the PMNT based cymbal transducer is much larger than that of the PZT based cymbal transducer. The electric performance of the cymbal transducers was also measured. The effects of material properties and the size of the metal caps on the displacement of the cymbal transducer are discussed.

Temperature dependence of the complete material coefficients matrix of soft and hard doped piezoelectric lead zirconate titanate ceramics

We have used resonance methods to determine the variation of all the independent piezoelectric, elastic, and dielectric material coefficients, as well as the corresponding electromechanical coupling factors, of soft and hard doped piezoelectric lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary, as a function of temperature ranging between −165 and 195°C. The material coefficients were obtained by analyzing the fundamental resonance of the impedance or admittance spectra as a function of frequency for several sample resonance geometries. The piezoelectric coefficients d33, −d31, and d15, as well as the dielectric permittivity coefficients ε11T and ε33T, generally increased with temperature for both soft and hard PZT samples. However, the elastic compliance coefficients s11E, −s12E, s33E, and s55E exhibited abnormal variations seen as broad peaks over parts of the tested temperature range. Additionally, thermal hystereses were observed in all the studied material coefficients over the temperature cycle. Finally, it was noted that, overall, the material coefficients of soft PZT varied significantly more than those of hard PZT under changing temperature conditions.

Temperature scaling of dynamic hysteresis in soft lead zirconate titanate bulk ceramic

The temperature scaling of the dynamic hysteresis was investigated in soft ferroelectric bulk ceramic. The power-law temperature scaling relations were obtained for hystersis area ⟨A⟩ and remnant polarization Pr, while the coercivity EC was found to scale linearly with temperature T. The three temperature scaling relations were also field dependent. At fixed field amplitude E0, the scaling relations take the forms of ⟨A⟩∝T−1.1024, Pr∝T−1.2322, and (EC0−EC)∝T. Furthermore, the product of Pr and EC also provides the same scaling law on the T dependence in comparison with ⟨A⟩.

Scaling behavior of dynamic hysteresis in soft lead zirconate titanate bulk ceramics

The scaling behavior of the dynamic hysteresis of ferroelectric bulk system was investigated. The scaling relation of hysteresis area ⟨A⟩ against frequency f and field amplitude E0 for the saturated loops of the soft lead zirconate titanate bulk ceramic takes the form of ⟨A⟩∝f−1∕4E0, which differs significantly from that of the theoretical prediction and that of the thin film. This indicates that the scaling relation is dimension dependent and that depolarizing effects in the interior must be taken into account to model bulk materials. Additionally, the scaling relation for the minor loops takes the form of ⟨A⟩∝f−1∕3E03, which is identical to that of the thin film as both cases contain similar 180° domain-reversal mechanism.

Ferroelastic domain switching in lead zirconate titanate measured by in situ neutron diffraction

Ferroelastic domain switching in a soft lead zirconate titanate (PZT) ceramic is measured by neutron diffraction on the texture diffractometer HIPPO with mechanical compression applied in situ. Complete orientation distribution functions are measured by time-of-flight neutron diffraction and represented as pole figures and inverse pole figures at compressive stresses in 50 MPa increments up to a maximum of 200 MPa. Significant domain switching hysteresis was observed in parallel to the macroscopic strain hysteresis. The contribution of ferroelastic domain switching to the measured macroscopic strain is calculated directly from the 0 0 l pole figure. Subtraction of this contribution from the measured macroscopic strain yields the bulk-averaged lattice strain. After unloading, the macroscopic strain of 0.30% consists of 0.22% ferroelastic domain switching and 0.08% crystallographic lattice strain.

Determination of room-temperature creep of soft lead zirconate titanate piezoceramics under static electric fields

This study focuses on the experimental investigation of the time-dependent effects of a commercial soft lead zirconate titanate material at room temperature. Samples in initially unpoled states were subjected to a cyclic stepwise electric field which was kept constant at different levels for 300 s. Due to ferroelectric domain switching, significant nonlinearity and hysteresis were observed in the overall polarization and strain response. In particular, the material exhibited creep behavior as the applied electric field was held constant over extended periods of time. This creep was caused by microscopic domain switching processes induced gradually during the holding time. The creep was of primary or transient type in nature and depended strongly on the magnitude of the load applied. Most pronounced creep was observed when holding the field close to the coercive field. Logarithmic representation of the polarization or strain versus time curves indicated that the creep behavior could be quantified approximately by the Andrade power law. The creep exponents were determined for different field conditions. The results may help the understanding of the creep mechanism, which in turn provides contributions to improve the performance and reliability of ultrahigh-precision positioning piezoactuators.

Analytical and experimental study of nonlinear bending response and domain wall motion in piezoelectric laminated actuators under ac electric fields

We investigate the nonlinear bending behavior of piezoelectric laminated actuators as a function of the amplitude and frequency of large electric fields both analytically and experimentally. Laminated beam theory is expanded to allow for the cantilever piezoelectric/metal/piezoelectric actuator, and the effects of alternating current (ac) electric fields on the tip deflection are analyzed. A simple phenomenological model of a vibrating domain wall in electric fields is used, and the macroscopic actuator response is predicted. A nonlinear three-dimensional finite element analysis is also employed. Experimental results are presented to validate the predictions using bimorph-type bending actuators made with thin soft lead zirconate titanate (PZT) layers and a thin metal sheet. Calculations show reasonable agreement with the experimental data, and support a role for domain wall motion in the nonlinear material response of the soft PZT under ac electric fields.