A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

Perspective on the Development of Lead-free Piezoceramics

After twenty years of partly quiet and ten years of partly enthusiastic research into lead-free piezoceramics there are now clear prospects for transfer into applications in some areas. This mimics prior research into eliminating lead from other technologies that resulted in restricted lead use in batteries and dwindling use in other applications. A figure of merit analysis for key devices is presented and used to contrast lead-containing and lead-free piezoceramics. A number of existing applications emerge, where the usage of lead-free piezoceramics may be envisaged in the near future. A sufficient transition period to ensure reliability, however, is required. The use of lead-free piezoceramics for demanding applications with high reliability, displacements and frequency as well as a wide temperature range appears to remain in the distant future. New devices are outlined, where the figure of merit suggests skipping lead-containing piezoceramics altogether. Suggestions for the next pertinent research requirements are provided.

Transferring lead-free piezoelectric ceramics into application

The electromechanical coupling in ferroelectric materials is controlled by several coexisting structural phenomena which can include piezoelectric lattice strain, 180 degrees and non-180 degrees domain wall motion, and interphase boundary motion. The structural mechanisms that contribute to electromechanical coupling have not been readily measured in the past, particularly under the low-to-medium driving electric field amplitudes at which many piezoelectric materials are used. In this feature, results from in situ, high-energy, and time-resolved X-ray diffraction experiments are interpreted together with macroscopic piezoelectric coefficient measurements in order to better understand the contribution of these mechanisms to the electromechanical coupling of polycrystalline ferroelectric materials. The compositions investigated include 2 mol% La-doped PbZr0.60Ti0.40O3, 2 mol% La-doped PbZr0.52Ti0.48O3, 2 mol% La-doped PbZr0.40Ti0.60O3, undoped PbZr0.52Ti0.48O3, and 2 mol% Fe-doped PbZr0.47Ti0.53O3. In all compositions, a strong correlation is found between the field-amplitude-dependence of the macroscopic piezoelectric coefficient and the contribution of non-180 degrees domain wall motion determined from the diffraction data. The results show directly that the Rayleigh-like behavior of d(33) piezoelectric coefficient is predominantly due to a Rayleigh-like behavior of non-180 degrees domain wall motion. Furthermore, after separating contributions from lattice (atomic level) and domain wall motion (nanoscale level) to the measured macroscopic piezoelectric properties, we show that previously ignored intergranular interactions (microscopic level) account for a surprisingly large portion of the electromechanical coupling. These results demonstrate that electromechanical coupling in polycrystalline aggregates is substantially different from that observed in single crystalline materials. The construct of emergence is used to describe how averaged macrolevel phenomena are different from the material response observed in an isolated subcomponent of the material. Consequently, and due to its size-scale complexity, the description of grain-to-grain interactions is presently inaccessible in most ab initio and phenomenological approaches. Results presented here demonstrate the need to account for these interactions in order to completely describe macroscopic electromechanical properties of polycrystalline materials.

Origins of Electro-Mechanical Coupling in Polycrystalline Ferroelectrics During Subcoercive Electrical Loading

Dielectric constant enhancement in a silicone elastomer filled with lead magnesium niobate–lead titanate

Local Structural Heterogeneity and Electromechanical Responses of Ferroelectrics: Learning from Relaxor Ferroelectrics

We have investigated the electromechanical response of piezoelectric ceramics as a function of the amplitude and frequency of large electric fields and studied the effects of dc bias fields In order to characterize the materials under these conditions, a ZMI 2000 laser interferometer system from Zygo Corp has been installed and modified to directly measure the strains of ferroelectric ceramics This system uses a heterodyne detection technique and has the advantages of phase detection, wide bandwidth, high stability, and easy optical alignment Our experiment has been used to determine the strain of lead zirconate titanate (PZT) ceramics as a function of electric fields and as a function of frequency in the low frequency range From these measurements the piezoelectric coefficients d33, d31, and d15 have been determined as a function of applied field and frequency In addition the dependence of the piezoelectric coefficients under an applied dc bias field has been studied under quasistatic and under res

Piezoelectric strain in lead zirconate titante ceramics as a function of electric field, frequency, and dc bias

Laser Doppler interferometry has been used to determine the strain and piezoelectric response of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) electrostrictive ceramics as a function of electric fields up to 4 MV m-1, frequencies between 01 Hz and 25 kHz and DC bias fields up to 3 MV m-1 The strain and polarization of PMN-15 with a composition of 09PMN-01PT and PMN-38 with a composition of 085PMN-015PT both produced by TRS ceramics, have been measured at room temperature The strain and polarization responses of PMN-15 ceramics under an electric field up to 4 MV m-1 have been fitted to a polynomial model The results suggest that a quadratic dependence of strain on polarization is not valid for large electric fields and that higher-order terms must be included Our measurements showed that the effective piezoelectric coefficient, d33, of PMN-15 ceramics had a maximum value of 800 pm V-1 at a bias field of 067 MV m-1 and had little frequency dependence in the frequency range from 1 Hz up to 25 kHz PMN-38 ceramic showed a maximum d33 of 1200 pm V-1 at a bias field of 043 MV m-1 and the d33 of this material showed a clear frequency dependence from 1 Hz up to 25 kHz

https://iopscience.iop.org/article/10.1088/0022-3727/35/13/316/pdf

Nonlinear strain and DC bias induced piezoelectric behaviour of electrostrictive lead magnesium niobate-lead titanate ceramics under high electric fields

We have measured some of the dielectric, elastic, and piezoelectric constants of several types of PZT piezoelectric ceramics, manufactured by EDO Corporation, as a function of applied electric field and mechanical stress. Both the high frequency impedance resonance method and the low frequency response of the material under electrical and mechanical excitations were employed to determine these constants. We present the dependence of these material constants on an applied DC bias voltage and on an applied mechanical stress. Most of the results can be understood on the basis of the extrinsic contributions to the piezoelectric response that arises from the existence of domains in the materials.

W. Ren

Papers

Piezoelectric strain in lead zirconate titante ceramics as a function of electric field, frequency, and dc bias

Nonlinear strain and DC bias induced piezoelectric behaviour of electrostrictive lead magnesium niobate-lead titanate ceramics under high electric fields

Effects of uniaxial stress and DC bias field on the piezoelectric, dielectric, and elastic properties of piezoelectric ceramics