Response Of Ferroelectric Ceramics Research Articles

Thermal-electrical like response in doped sodium bismuth titanate-based ferroelectric ceramics

The flexoelectric effect, a type of electromechanical property, is proposed to generate thermal-electrical like response in ferroelectric ceramics; however, presently, the electric current output achieved is small. Here, we show that changing the composition of the Na0.5Bi0.5TiO3-based ceramics to improve their conductivity can enhance their thermal-electrical like response to several orders of magnitude larger than that reported earlier. We also found that the measured thermal-electrical like response mainly originates from the spontaneously polarised surface existing in ferroelectrics, which generates a flexoelectric-like response under inhomogeneous deformation. The coupling of the flexoelectric-like response and high conductivity leads to a large thermal-electrical like response.

Flexoelectric response of ferroelectric ceramics with reduced surface layer effect

The flexoelectric response of Na0.5Bi0.5TiO3-based and (Ba,Sr)TiO3 ferroelectric ceramics with sputtered or fired-on Ag, Au, and Ag/Pd electrodes was investigated. We found that for all the ceramics, the flexoelectric response of the same material is strongly dependent on the methods used to fabricate the electrodes. The samples with fired-on electrodes have a much smaller flexoelectric response than those with sputtered electrodes, and for a certain composition, the flexoelectric response can be reduced by more than 99%. The reduction of flexoelectric response is attributed to the suppression of the contribution from the spontaneously polarized surface layers on ferroelectric ceramics to the flexoelectric response. Three reasons were proposed for the suppression of the surface effect, namely, the diffusion of some substances in electrode pastes to the surface regions of ferroelectric ceramics, stress relief, and the generation of impurity phases caused by the evaporation of volatile element during the firing of electrode materials at a high temperature. We also found that the flexoelectric response can approach the theoretically predicated response after the surface effect is reduced by fabricating fired-on electrodes on ferroelectric ceramics. Our results indicate that the large flexoelectric response of ferroelectric ceramics is mainly from the polarized surface layers and the surface effect is the primary mechanism leading to the deviation of measured flexoelectric response from the intrinsic response in ferroelectric ceramics, which has been an unresolved issue in the flexoelectric research field.

Piezoelectricity in perovskite-type pseudo-cubic ferroelectrics by partial ordering of off-centered cations

A large piezoelectric response in ferroelectric ceramics is typically associated with extrinsic contributions from ferroelectric domain structures. However, such domain structures cannot be expected in systems with pseudo-cubic symmetry. In this study, we determine the mechanism of significant piezoelectricity and ferroelectricity in 0.3BaTiO3–0.1Bi(Mg1/2Ti1/2)O3–0.6BiFeO3 ceramic with a perovskite-type pseudo-cubic symmetry. Synchrotron radiation X-ray diffraction reveals that the Bi ions in this ceramic essentially prefer to be off-centered at six sites by approximately 0.4 Å, in the cubic <100> directions. A phase transition occurs at TC ~725 K. However, the crystal seems to present a cubic symmetry even at room temperature. The large piezoelectric response is caused by the combinational partial ordering of the off-centered Bi ions, adapted to any direction of the applied electric field to the ceramic grains. The proposed mechanism for the emergence of a high polarization in the above system will enable designing novel Pb-free ceramics by controlling the fluctuated and off-centered ions under an applied electric field.

Flexoelectricity in ferroelectric materials

Flexoelectricity is a gradient electromechanical effect that exists in all solid dielectrics. The effect was first predicted in the late 1950s, but received little interest because it was expected to be small. The experimentally measured large flexoelectric response in ferroelectric ceramics led to the revival of the field in the early 2000s. In this study, the progress made in the flexoelectric field is reviewed. The authors' focus will be primarily on the experimental studies related to the flexoelectric effect. The techniques employed to measure the flexoelectric coefficients are first summarised. A compilation of the flexoelectric coefficients of different ferroelectrics reported in the literature will be presented. An unresolved issue in this field is that the measured flexoelectric coefficients in ferroelectric materials are normally much greater than the theoretically predicted values, and the mechanisms proposed to explain this issue are discussed. Finally, the efforts toward the applications of the flexoelectric effect are reviewed.

Off-stoichiometry, structural-polar disorder and piezoelectricity enhancement in pre-MPB lead-free Na0.5Bi0.5TiO3-BaTiO3 piezoceramic

With increasing industrial acceptance of Na0.5Bi0.5TiO3 (NBT)-based lead-free piezoceramics, there is a need to develop insights into the way different factors influence the microstructural–structural–piezoelectric property correlations. In this work, we have examined the role of structural disorder on the piezoelectric response of the pre-MPB composition x = 0.03 of the well-known solid solution series (1-x)Na0.5Bi0.5TiO3-(x)BaTiO3. Using off-stoichiometry on the A-site as a tuning parameter to vary the structural disorder, which we characterize in terms of the fraction of the “cubiclike phase” or variation in the thermal parameter of the A-site cation, it is shown that the piezo response maximizes for the composition, which retains an optimum degree of disorder after poling. Our study confirms the important role of structural disorder in enhancing piezoelectric response in ferroelectric ceramics.

Kinetically stabilized metastable polarization states in ferroelectric ceramics

By directly using experimental hysteresis loop data, a Landau theory-based model has been developed to investigate the effects of externally applied stimuli (electric field, stress, and temperature) on the average, time-dependent response in ferroelectric ceramics. For both PLZT and BNT-BT-KNN systems, experimentally observed (macroscopic) metastable states are a result of a free energy minimum that develops at a zero polarization state when the sample is subject to an externally applied field. Additionally, the frequency dependent hysteresis response demonstrates that a transition between relaxor ferroelectric and antiferroelectric develops at a critical cycling frequency, in agreement with the literature. The appearance of frequency-induced and electric field amplitude-induced kinetically stabilized phases is proposed and summarized in terms of frequency-stress and frequency-temperature response maps.

Enhancement of the electromechanical response in ferroelectric ceramics by design

It is demonstrated based on continuum mechanics modeling and simulation that it is possible to obtain polycrystalline ceramic ferroelectric (FE) materials which beggar single crystals in electromechanical properties. The local inhomogeneities at the FE domain-scale level due to spontaneous polarization and the underlying anisotropy are taken into consideration in the framework of mathematical homogenization of physical properties in FE materials. The intrinsic randomness of the spatial distribution of polarization is shown to be judiciously employed for the design of better polycrystalline FEs. The noncollinear rotation of the net polarization vectors embedded in crystallites of the ceramic FEs is demonstrated to play the key role in the enhancement of physical properties.

Direct measurement of the domain switching contribution to the dynamic piezoelectric response in ferroelectric ceramics

The dynamic piezoelectric response of ferroelectric ceramics is comprised of both intrinsic (piezoelectric lattice strain) and extrinsic (non-180° domain wall motion) components. Here the authors report direct measurements of non-180° domain wall motion in ceramic lead zirconate titanate during application of subcoercive cyclic driving electric fields using an in situ stroboscopic neutron diffraction technique. During unipolar cycling at 1Hz and half of the coercive field, non-180° domain switching gives rise to approximately 34% of the measured d33 coefficient of 400pm∕V.

Nonlinear contributions to the dielectric permittivity and converse piezoelectric coefficient in piezoelectric ceramics

A measurement and analysis technique has been developed to quantify the complex contributions to the nonlinear dielectric and converse piezoelectric response in ferroelectric ceramics. The electric field dependent response was quantified in two important bulk ceramic piezoelectric systems, Pb(Zr1−x,Tix)O3 and (1−x)BiScO3–xPbTiO3 (BS-PT), at low frequency and room temperature. The nonlinear response was shown to obey the Rayleigh law in the specific field and frequency ranges reported. Analysis of BS-PT perovskites with different crystal structures revealed a ferroelectric phase dependence on the magnitude of the nonlinear contribution to the dielectric and piezoelectric responses. The magnitudes of the nonlinear coefficients, which quantify the irreversible extrinsic response, were found to be smallest in the ferroelectric tetragonal phase, larger in the rhombohedral composition, and highest at the morphotropic phase boundary. Finally, this work provides strong evidence that the same loss mechanism dominates the nonlinear portion of both the dielectric and piezoelectric responses in piezoelectric ceramics. Analysis of these contributions supports an earlier theoretical model inferring that non-180° domain wall motion in bulk ferroelectric ceramics is a major factor in the piezoelectric and dielectric responses. These results link the observed Rayleigh law behavior to the mechanistic domain wall model commonly employed to describe the extrinsic response of ferroelectric ceramics.

Effects of Lateral Stress on the Electromechanical Response of Ferroelectric Ceramics: Experiments versus Model

Mechanical depolarization is an important cause of failure in piezoelectric actuators and sensors. In this paper, the effects of one-dimensional lateral pressure on the linear and nonlinear behavior of PZT ceramics were experimentally studied. The experimental results show that the lateral pressure can change the crystal symmetry of the ceramic from 1mm to mm2. A domain-switching model dividing each 180 switching to two successive 90 switching is proposed to explain the experimental results. Finally, based on the experimental results, a simple design is proposed to prevent piezoelectric sensors from mechanical depolarization. Meanwhile, the simple design is apt to increase the hydrostatic piezoelectric constant of the piezoelectric marine sensors, thus enhancing their sensitivity.

Reversible and irreversible piezoelectric and ferroelectric response in ferroelectric ceramics and thin films

Abstract In this article, a novel characterization method, the separation between reversible and irreversible contributions, is applied to the piezoelectric and ferroelectric response of ferroelectric ceramics and thin films. The reversible contributions are determined by the measurement of appropriate small-signal properties, e.g. the piezoelectric coefficient for the piezoelectric response and the small-signal capacitance for the polarization response of the material, and compared to the corresponding large signal properties (i.e. the strain–field dependence and polarization–field dependence, respectively). The comparison between thin films and bulk ceramics indicates that the non-180° domain wall motion in ferroelectric thin films is reduced compared to bulk ceramics.

Dissipative Domain Wall Motion and Macroscopic Response of Ferroelectric Ceramics

We present a model which is based on the notion of a polycrystalline material with grains having a lamellar domain structure. The domain stack is homogenized by analytical methods whereas the interaction of grains is taken into account by the effective medium approximation. Domain wall motion is allowed to take place by considering the total potential energy variation of the polycrystalline material in comparison with microscopic retarding forces. The model is numerically evaluated with data for barium titanate single-crystals. Thus the hysteretic material behavior occurring under large-signal unipolar loading can be correlated with the dissipative domain wall motion. We also get some quantitative information on the fluctuating internal fields.

Dissipative Domain Wall Motion and Macroscopic Response of Ferroelectric Ceramics

Dissipative Domain Wall Motion and Macroscopic Response of Ferroelectric Ceramics

Electromechanical properties and domain-related effects in ferroelectric thin films

The possibility of miniaturization and integration with silicon technology makes ferroelectric films promising for micro sensors and micro actuators. Despite the increasing range of applications, the electromechanical properties of thin-layer ferroelectrics are poorly understood as compared to those of bulk materials. In particular, it is an open question whether the non-180° domain motion, which determines the strain response in ferroelectric ceramics, contributes to electric field-induced strain in thin films. This paper reviews author's recent investigations on electromechanical properties of ferroelectric thin films, with special emphasis on domain-related effects. The materials list includes Pb(Zr,Ti)O3 (PZT), Pb(Ca,Ti)O3 (PCT) and SrBi2Ta209 (SBT). It is shown that in some cases the non-180° domain wall contribution is necessary to describe the mechanical strain under sufficiently high electric field. This contribution is found to be important for PZT films of the morphotropic phase boundary and rhombohedral compositions. In PCT films the strain response as a function of Ca content is explained based on the reorientation of 90° domains. In SBT films pure electrostrictive relationship is found between the strain and polarization suggesting that the non-180° domains are either absent or inactive in this material.

One Dimensional, Linear Dynamic Electromechanical Responses of Ferroelectric Ceramics

In this paper we consider the coupled electromechanical responses of poled ferroelectric ceramics. Our considerations are linear as well as one dimensional. The constitutive relations which characterize the stress and the electric field in terms of the strain and the electric displacement reflect the fact that the responses of such a material are time dependent. These time dependent processes arise principally because domain switching, due to mechanical loadings and the application of external electric fields, does not occur instantaneously as well as due to other mechanical and electrical relaxation effects. We then formulate the boundary-initial value problems which correspond to the voltage mode, finite resistance, and pulse poling and depoling experiments. These problems are solved using Laplace transform technique, and numerical inversions of the transform solutions are obtained by utilizing the method outlined by Luke and Salzer.