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Currently available high performance piezoelectric materials, predominantly based on lead zirconate titanate (PZT), are typically limited to operating temperatures of around 200 °C or below. There are many applications in sectors such as automotive, aerospace, power generation and process control, oil and gas, where reliable operation at higher temperatures is required for sensors, actuators and transducers. New materials are being actively developed to meet this need. Development and application of new and existing materials requires reliable measurement of their properties under these challenging conditions. This paper reviews the current state of the art in measurement of piezoelectric properties at high temperature, including direct and converse piezoelectric measurements and resonance techniques applied to high temperature measurements. New results are also presented on measurement of piezoelectric and thermal expansion and the effects of sample distortion on piezoelectric measurements. An investigation of the applicability of resonance measurements at high temperature is presented, and comparisons are drawn between the results of the different measurement techniques. New results on piezoelectric resonance measurements on novel high temperature piezoelectric materials, and conventional PZT materials, at temperatures up to 600 °C are presented.

Single crystal (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 [PMN-xPT] (x=0.32) is a relaxor-ferroelectric material known to exhibit `giant' piezoelectric behaviour, with achievable strains in excess of 1% for samples of certain particular crystallographic orientations and chemical compositions close to the morphotropic phase boundary (MPB). In this paper, we investigate the electric field-nduced structural phase transitions in single crystal PMN-0.32PT with time-of-flight neutron diffraction and macroscopic electrical polarisation measurements, and show that both the frequency of the applied ac field and the temperature of the sample are critical factors in determining these phase transition fields.

Piezoelectric ZnO nanorods grown on a flexible substrate are combined with the p-type semiconducting polymer PEDOT:PSS to produce a p-n junction device that successfully demonstrates kinetic-to-electrical energy conversion. Both the voltage and current output of the devices are measured to be in the range of 10 mV and 10 μA cm−2. Combining these figures for the best device gives a maximum possible power density of 0.4 mW cm−3. Systematic testing of the devices is performed showing that the voltage output increases linearly with applied stress, and is reduced significantly by illumination with super-band gap light. This provides strong evidence that the voltage output results from piezoelectric effects in the ZnO. The behavior of the devices is explained by considering the time-dependent changes in band structure resulting from the straining of a piezoelectric material within a p-n junction. It is shown that the rate of screening of the depolarisation field determines the power output of a piezoelectric energy harvesting device. This model is consistent with the behavior of a number of previous devices utilising the piezoelectric effect in ZnO.

ZnO nanorods grown on plastic substrates by chemical methods are combined with both inorganic and organic p-type materials to make flexible p-n junction devices. When bent the devices generate both voltage and current peaks, which is attributed to the piezoelectric effect in the ZnO nanorods. The best device produces a maximum possible power density of 100 nWcm‑2. When vibrated at a constant frequency the voltage output by the devices scales linearly with vibration amplitude. Also, when illuminated the output of the devices drops. These effects are consistent with a piezoelectric source of the voltage.

Piezoelectric materials are used in many applications, at increasingly smaller scales. Methods of measuring their hydrostatic properties have been developed where the piezoelectric charge is produced as a result of a varying hydrostatic pressure generated within a sealed chamber. In this paper, the authors explore an anomalous generation of charge in thin laminar samples and show this is a result of the pyroelectric effect. The authors model the change in temperature in the sealed chamber caused by the adiabatic expansion of the gas and relate this to the observed generation of charge, using finite element modelling to investigate the temperature profile through the material. The implications of these results are relevant for the successful integration of piezoelectric thin and thick films into MEMS devices.

The Active Fibre Composite (AFC) has been the subject of much interest as a smart technology that can be embedded into host structures for adaptive shape control and structural health monitoring. The electromechanical performance of these devices has been extensively studied, although the structural properties have received little attention. Knowledge of the mechanical performance of the AFC is essential to prevent loss of performance and failure. Experimentally measured tensile strengths of PZT fibre—epoxy composites were found to contradict the behaviour predicted by simple composite theory. It has been shown that the selection of appropriate matrix material is an essential factor in controlling the failure mode of active composites.

A novel system for characterizing the spatial variation of piezoelectric properties of piezoelectric ceramic samples has been developed and tested in a series of case studies. The system has been shown to be capable of detecting various types of defects in PZT ceramic materials including localized sample depoling brought about through thermal and mechanical treatments. It has also been used to detect defects due to environmental degradation under high dc bias. The present system can be used as an R&D tool, but with further developments to increase the scanning speed the technique could be extended for use in a Quality Assurance environment.

The piezoelectric, microstructural and electrical characteristics of thick PZT films on relatively inert alumina substrates and on two LTCC tapes, i.e., Du Pont 951 and Electro Science Labs 41020 were studied. A thick-film paste was prepared from the pre-reacted PZT powder (PbZr0.53Ti0.47O3) and printed and fired on LTCC tapes and on alumina substrates, respectively. Dielectric permittivities, dielectric losses, remnant polarizations and coercive fields were measured. The dielectric constants (100–150) of thick films fired on LTCC substrates are low. The piezoelectric coefficients d 33 were measured by different methods, i.e. Berlincourt piezometer, interferometry and piezoresponse force microscope (PFM). The d 33 values on LTCC substrates are low (30–70 pm/V) as compared with values obtained on alumina substrates (around 120 pm/V). Lower dielectric constants and piezoelectric coefficients d 33 of films on LTCC substrates are attributed to the formation of phases with a low permittivity due to the diffusion of silica from LTCC substrates into PZT films. The d 33 constants of samples with different thicknesses of PZT layers (from 20 to 160 μm) at first increase with the increasing thickness of PZT layers and then decrease for thicker films. As the cracks in the structure were not observed the reason for the decreasing d 33 values for thicker films is still unclear.

Piezoelectric devices with complex electrode geometries may contain regions of ferroelectric material that remain unpoled. It is desirable to account for these non-piezoelectric regions for device optimization, since the unpoled and poled material properties differ. The lack of published elastic properties for unpoled ferroelectrics, specifically the numerous commercial PZT compositions, reflects the difficulty of experimental measurement. In this work, a method was developed to predict unpoled properties from more commonly available poled material data. Barium titanate was chosen for study as a representative ferroelectric, with both single crystal and polycrystalline (ceramic) properties available. Finite element micro-mechanical models were created with a focus on computational economy. This allowed larger ensembles of results to be computed, providing accurate effective compliances when averaged. The modelling methodology predicted the elastic properties for unpoled barium titanate to within ∼10% of measured experimental values.

Composite actuators and sensors manufactured by combining a ferroelectric ceramic such as lead zirconate titanate and a passive phase such as a polymer are used in a variety of applications including SONAR, vibration damping, change of structural shape (morphing), and structural health monitoring. The composite route provides specific advantages, including tailored piezoelectric response, high strain, a degree of flexibility, and increased damage tolerance compared with conventional dense monolithic ceramic materials. For piezoelectric fibre composites, where fine-scale brittle ceramic fibres of 40–800 μm diameter are introduced into a ductile polymer matrix, the composite strength and failure mechanism ultimately depend on the mechanical properties of each phase and their volume fraction. This article examines the mechanical properties of piezoelectric fibres and the matrix phase and discusses the possible influence of fibre volume fraction on mechanical properties and failure mechanism of the composite. The data are of particular use in determining the failure stress, failure strain, and failure mechanism of composite actuators and sensors subjected to high levels of stress, for example, in applications where such devices are embedded into host structures.

The optimisation of the interdigitated electrode (IDE) design for active fibre composites was performed using finite element analysis. The effect of the IDE geometry (electrode width and spacing) and electroceramic substrate thickness on the developed strain for bulk PZT substrates was modelled. The modelling results show that the highest strain is generated when the electrode width equals half the substrate thickness and for thin substrates the electrode finger spacing can be reduced to enable lower driving voltages. Approximately 80% of the maximum d33 strain can be achieved with an electrode separation to substrate thickness ratio greater than 4. The results present simple coherent guidelines for the optimisation of electrode geometry for piezoelectric actuators and active fibre composites.

Piezoelectric fibres are finding increasing application in a variety of piezoelectric composites, including active fibre composites (AFCs). This paper describes the manufacture and characterization of lead zirconate titanate (PZT) fibres manufactured by viscous plastic processing (VPP). The manufacturing method will be described along with a systematic characterization of the macrostructure, microstructure, phase composition and low and high field piezoelectric properties. A comparison with other available PZT fibres will be made, which demonstrates that the VPP PZT fibres display high piezoelectric coefficients.

A methodology for the measurement of high field strain and polarisation responses of fine scale piezoelectric fibres is presented. Using analytical models, the response of the fibres is extracted from measurements made on 1–3 composites. Analytical modelling shows that composites with a high fibre volume fraction are desirable for accurate prediction of the fibres response. Poor model response at low fibre volume fractions is attributed to non-linear material properties, and deviation from the model assumptions.

This chapter provides detail of standards-related activities for piezoelectric materials—mainly bulk ceramic types. The production of standards, particularly international ones, is a long process. The existence or not of a standard in a particular area is not solely because of the need for such a standard, but is due to the concerted effort of individuals. Documents must be kept current, and may be withdrawn or cancelled if there is nobody prepared to maintain it after publication. There are strong groups for piezoelectric materials standards in Europe (CENELEC) and America (IEEE-UFFC), but some of the most quoted standards have been withdrawn (IEEE 176-1987 [1], IEEE 180-1986, MIL-STD 1376B (SH)). An updated and regularly reviewed set of standards can be found at http://www.piezoinstitute.com.

Historically, the method defined by IEEE has been used extensively to analyse the resonance spectra of piezoelectric materials. Here, the resonance frequencies from a set of samples of different geometries are measured and along with their dimensions and sample density the piezoelectric coefficients determined. This method is simple to carry out in principle, and the calculations are relatively straightforward (although the wave equations for some of the geometries must be solved empirically through the use of Bessel functions).

There are many uses of piezoelectric ceramics where the desire for increased power output means increased drive levels, which subsequently can lead to thermal problems within the device.

Although piezoelectric materials are often used as actuators in order to make small precise movements it can be difficult to measure these displacements in an industrial environment [1].

Recent developments on the use of the piezoelectric effect in ZnO nanorod-based p-n junctions for energy harvesting applications are presented. Two types of junctions are used. The first is a hybrid p-n device combining the semiconducting polymer poly(3,4-ethylene-dioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) with ZnO nanorods. The second type of junction is an all-inorganic junction between n-type ZnO nanorods and p-type CuSCN. It is shown that both these diodes can be produced on flexible plastic substrates, which generate a voltage output when bent. The voltage output of the ZnO/PEDOT:PSS diodes are measured across a range of resistive loads while bending to find a maximum power point of 12 μWcm-2 at 4 kΩ. It is shown that a voltage output is also generated when this structure is vibrated acoustically. The ZnO/CuSCN diode is sensitized to sunlight with a Ru-based dye to form a photovoltaic device. It is shown that the device efficiency can be increased by application of acoustic vibrations. This is attributed to the electric field generated by the piezoelectric effect in ZnO affecting the charge-carrier recombination at the ZnO surface.

Methods for the high stress characterisation of piezoelectric ceramics have been examined. Displacement measuring techniques have been compared, with fibre optic probes being the most practical. A method for measuring displacement variations over a surface area has been developed and used on a multilayer ceramic. Mechanical degradation of piezoelectrics has been performed using an electromagnetic actuator in a resonating system at 230Hz, with loads of 20kN, and for over 108 cycles.

The characteristics of a new ferroelectric measurement system at the European Synchrotron Radiation Facility are presented. The electric-field-induced phase transitions of Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) are determined via in situ measurements of electric polarization within the synchrotron diffraction beamline. Real-time data collection methods on single-crystal samples are employed as a function of frequency to determine the microstructural origin of piezoelectric effects within these materials, probing the dynamic ferroelectric response.

The functional properties of ferroelectric ceramic bulk or thin film materials are strongly influenced by their nano-structure, crystallographic orientation and structural geometry. In this paper, we present a possible route to quantification of piezoresponse force microscopy (PFM) by combining it with textural analysis, through electron back-scattered diffraction (EBSD). Quantitative measurements of the piezoelectric properties can be made at a scale of 25 nm, smaller than the domain size. The combined technique is used to resolve the effective single crystal piezoelectric response of individual crystallites in polycrystalline lead zirconate titanate (PZT). The piezoresponse results are quantified via two methods and these are compared to the piezoresponse predicted by a model. The results are encouraging for the quantification of the PFM technique and promote it as a tool for the future development of new nano-structured ferroelectric materials such as memory, nano-actuators and sensors. Knowledge of the orientation at the nanoscale allows for a method of quantification of the PFM signals and is being pursued as one method with which to potentially provide standards for PFM. This pre-standards work continues under a new VAMAS (Versailles Project on Advanced Materials and Standards) initiative. Standardization will provide a way to meaningfully compare values recorded with the PFM technique, which has become an important tool in the characterization of piezoelectric and ferroelectric materials.

Electrostriction plays a central role in describing the electromechanical properties of ferroelectric materials, including widely used piezoelectric ceramics. The piezoelectric properties are closely related to the underlying electrostriction. Small-field piezoelectric properties can be described as electrostriction offset by the remanent polarization which characterizes the ferroelectric state. Indeed, even large-field piezoelectric effects are accurately accounted for by quadratic electrostriction. However, the electromechanical properties deviate from this simple electrostrictive description at electric fields near the coercive field. This is particularly important for actuator applications, for which very high electromechanical coupling can be obtained in this region. This paper presents the results of an experimental study of electromechanical coupling in piezoelectric ceramics at electric field strengths close to the coercive field, and the effects of temperature on electromechanical processes during polarization reversal. The roles of intrinsic ferroelectric strain coupling and extrinsic domain processes and their temperature dependence in determining the electromechanical response are discussed.

A new materials characterization system developed at the XMaS beamline, located at the European Synchrotron Radiation Facility in France, is presented. We show that this new capability allows to measure the atomic structural evolution (crystallography) of piezoelectric materials whilst simultaneously measuring the overall strain characteristics and electrical response to dynamically (ac) applied external stimuli.

The determination of the piezoelectric coefficient of thin films using interferometry is hindered by bending contributions. Using finite element analysis (FEA) simulations, we show that the Lefki and Dormans approximations using either single or double-beam measurements cannot be used with finite top electrode sizes. We introduce a novel method for characterising piezoelectric thin films which uses a differential measurement over the discontinuity at the electrode edge as an internal reference, thereby eliminating bending contributions. This step height is shown to be electrode size and boundary condition independent. An analytical expression is derived which gives good agreement with FEA predictions of the step height.

Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72. Measurements of the piezoelectric induced strain constants (d33 and d31), relative dielectric constants (e33), longitudinal coupling factors (k33) and stiffness' (s33) of the varying volume fraction composites are compared to analytical expressions in order to extract the fibre properties. Results show 1-3 composite data accurately follows the analytical trends. The Viscous Plastic Process (VPP) fibres are found to exhibit optimum material properties, which approach bulk material values. Reduced piezoelectric activity in extruded fibres is thought to be associated with a small grain size and high porosity. A second study, an optimisation of interdigitated electrode design, was performed using the finite element software ANSYS. The effect of the IDE geometry (electrode width and spacing) and PZT substrate thickness on the strain output of bulk PZT substrates was modelled. Results show optimal actuation occurs at electrode widths equal to half the substrate thickness, and for thin substrates the electrode finger spacing can be reduced to enable lower driving voltages.

This paper analyses strain and polarisation responses of 1-3 composites, which are related to the fibre and matrix properties. The validity of equations that predict the strain and polarisation of fibres from composite responses, and associated errors at high electric driving fields, are discussed. Surface profile measurements of single PZT rods in a polymer matrix, subjected to a static voltage, were made to investigate the effect of fibre aspect (diameter to length) ratio. Surface profiles, which show the active PZT rod extending from the passive polymer matrix, agree well with predictions made using finite element analysis. The results show that for a 1-3 composite to be treated as a homogeneous medium the fibre aspect ratio needs to be low. Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72, and with various aspect ratios, were evaluated. Strain-field and polarisation-field curves for the composites were obtained by testing the composites under electrical field cycles of ±2 kVmm-1. From these curves the strain and polarisation response of the fibres have been extracted using appropriate analytical equations. The saturation strain, saturation polarisation and coercive field values are reported for the four fibre types. The Viscous Plastic Process (VPP) and Viscous Suspension Spun (VSSP) fibres develop strains of approximately 4000 ppm. Reduced piezoelectric activity is seen in extruded fibres, which develop strains of 3000 ppm.

Here, we study the piezoresponse of epitaxial ferroelectric samples excited through top electrode structures with conductive tips in the global excitation mode and compare these results to displacement values obtained using artifact-free laser Doppler vibrometry (LDV) measurements. Substrate bending modes are studied using finite element simulations and LDV measurements and found to be negligible for top electrode diameters below 100 μm. The effect of electrostatic forces on the piezoresponse measurements is analyzed and methods for minimizing these are discussed. Using a resistive tip-electrode contact mode, the piezoresponse measurements are found to be in good agreement with values obtained from calibrations, providing a link between nanometer scale piezoresponse measurements and quantitative LDV measurements.

A vertical levitation electrostatic comb drive actuator was manufactured for the purpose of measuring piezoelectric coefficients in small-scale materials and devices. Previous modelling work on comb drive levitation has focussed on control of the levitation in standard poly-silicon devices in order to minimize effects on lateral modes of operation required for the accelerometer and gyroscope applications. The actuator developed in this study was manufactured using a 20 μm electroplated Ni process with a 25 μm trench created beneath the released structure through chemical wet etching. A finite element analysis using ZINC was used to model electrostatic potential around a cross section of one static and one movable electrode, from which the net levitation force per unit electrode was calculated. The model was first verified using the electrode geometry from previously studied systems, and then used to study the variation of force as a function of decreasing substrate-electrode distance. With the top electrode surfaces collinear the calculated force density is 0.00651 0V2Mμm−1, equivalent to a total force for the device of 36.4 μN at an applied voltage of VM=100 V, just 16% larger than the observed value. The measured increase in force with distance was smaller than predicted with the FEA, due to the geometry of the device in which the electrodes at the anchored ends of the supporting spring structure displace by a smaller amount than those at the centre.

A micro-electro-mechanical systems (MEMS) vertical levitation comb drive actuator has been created for the measurement of piezoelectric coefficients in thin/thick films or piezoelectrically active micro-scale components of other MEMS devices. The device exerts a dynamic force of 33 μN at an applied voltage of 100 V. The charge developed on the piezoelectric test device is measured using a charge sensitive pre-amplifier and lock-in technique, enabling measurements down to 1×10−5 pC. The system was tested with ten different piezoelectric samples with coefficients in the range 70–1375 pC N−1 and showed a good correlation (r = 0.9997) to measurements performed with macroscopic applied stresses, and piezoelectric impedance resonance techniques. The measurement of the direct piezoelectric effect in micro- and nano-scale piezo-materials has been made possible using MEMS processing technology. This new application of a MEMS metrology device has been developed and fully characterized in order to accurately evaluate the functional properties of piezoelectric materials at the scale required in micro- to nano-scale applications.

Electromechanical energy harvesting converts mechanical energy from the environment, such as vibration or human activity, into electrical energy that can be used to power a low power electronic device. Nanostructured piezoelectric energy harvesting devices, often termed nanogenerators, have rapidly increased in measured output over recent years. With these improvements nanogenerators have the potential to compete with more traditional micro- or macroscopic energy harvesting devices based on piezoelectric ceramics such as lead zirconate titanate (PZT), polymers such as polyvinylidene fluoride (PVDF) or electrostatic, electret or electromagnetic kinetic energy harvesters. Power output from a nanogenerator is most commonly measured through open-circuit voltage and/or short-circuit current, where power may be estimated from the product of these values. Here we show that such measures do not provide a complete picture of the output of these devices, and can be misleading when attempting to compare alternative designs. In order to compare the power output from a nanogenerator, techniques must be improved in line with those used for more established technologies. We compare ZnO nanorod/poly(methyl methacrylate) (PMMA) and ZnO nanorod/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) devices, and show that despite an open-circuit voltage nearly three times lower the ZnO/PEDOT:PSS device generates 150 times more power on an optimum load. In addition, it is shown that the peak voltage and current output can be increased by straining the device more rapidly and therefore time-averaged power, or time-integrated measures of output such as total energy or total charge should be calculated. Finally, the internal impedance of the devices is characterised to develop an understanding of their behaviour and shows a much higher internal resistance but lower capacitive impedance for the ZnO/PMMA device. It is hoped that by following more rigorous testing procedures the performance of nanostructured piezoelectric devices can be compared more realistically to other energy harvesting technologies and improvements can be rapidly driven by a more complete understanding of their behaviour.

Prolonged operation of piezoelectric ceramic devices under high dc electric fields promotes leakage currents between the electrodes. This paper investigates the effects of ceramic porosity, edge conduction and electrode materials and geometry in the development of low resistance conduction paths through the ceramic. Localized changes in the ceramic structure and corresponding microscopic breakdown sites are shown to be associated with leakage currents and breakdown processes resulting from prolonged operation in harsh environments. The role of barrier coatings in mitigating the effects of humidity is studied, and results are presented on improved performance using composite diamond-like carbon/polymer coatings. In contrast to the changes in the electrical properties of the ceramic, the measurements of the piezoelectric properties showed no significant effect of humidity.

Jenny Wooldridge, John F. Blackburn, Neil L. McCartney, Mark Stewart, Paul Weaver et al. Citation: J. Appl. Phys. 109, 079901 (2011); doi: 10.1063/1.3572036 View online: http://dx.doi.org/10.1063/1.3572036 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v109/i7 Published by the AIP Publishing LLC.

The recent trend in miniaturization of piezoelectrically active devices is driving research on size effects of these functional materials under reduced length scales. In this paper, we measure and model the generation of charge in thin piezoelectric structures under sinusoidal hydrostatic pressure and show how the subsequent thermally induced pyroelectric effect dominates the response in the smallest samples. We calculate the temperature profiles through the lead zirconate titanate structures, and determine the pyroelectric coefficient in these materials to be p′=0.28±0.02 mC m−2 K−1. The analysis of the piezoelectric and pyroelectric charge response described in this paper has significant impact on the design and fundamental functional behavior of small-scale piezoelectric devices.

The Laser Intensity Modulation Method (LIMM) has traditionally been used to characterise the depth dependence of polarisation of piezoelectric materials1. Although the technique is simple, it is difficult to extract the polarisation / depth data from the measured pyroelectric current because of the complex mathematics pertaining to the physics of the technique. However, the laser probe may still be used as a comparative or qualitative tool in mapping out the polarisation across the surface of a material. A novel scanning LIMM system has been developed to map the variation in piezoelectric activity across a range of samples. The system has been upgraded with a galvanometer mirror scanner to increase speed and reduce sensitivity to acoustic noise. The improvements are discussed and tested on a range of case studies. The technique can be used to show differences in piezoelectric activity caused by features such as inhomogeneous material composition, porosity and mechanical damage. The method has application as a quality control tool for materials and device manufacturers.

Multiferroic materials exhibit a coupling between their intrinsic electric and magnetic fields known as magnetoelectric (ME) coupling. The ME coupling can be stress-mediated and is induced either magnetically or electrically. The linear ME coupling coefficient, α, gives a comprehensive description of this effect. However, the experimental determination of α is rather complex. In this paper, we report a simple and convenient experiment for the measurement of the magnetically induced ME coupling coefficient. Our experiment is based on the quasi-static piezoelectric coefficient measurement under applied magnetic field and can provide simultaneously the d33 piezo-coefficient of a multiferroic sample and the magnetically induced α coefficient as a function of both applied ac and dc magnetic fields.