High Electrostrictive Strain Research Articles

Simultaneously achieving high energy storage performance and low electrostrictive strain in BT‐based ceramics

AbstractDielectric ceramics with high recoverable energy storage density (Wrec) and high energy storage efficiency (η) are urgently needed due to their potential application in pulse capacitor devices. However, the low η and breakdown strength (BDS) have produced a bottleneck for achieving high Wrec at high electric field. Here, we introduce Bi(Mg0.5Ti0.5)O3 (BMT) into Ba(Ti0.92Sn0.08)O3 (BTS) matrix to enhance the relaxor character of BTS–xBMT and reduce the electrostrictive strain generated during electric field loading. The enhanced relaxor character is beneficial for increasing the efficiency, whereas the reduced electrostrictive strain is profitable to increase the BDS. Furthermore, the BDS is significantly improved by the polymer viscous rolling process. Finally, the electrostrictive effect was considerably lowered in an optimized BTS–0.1BMT composition. More crucially, a high Wrec of 4.34 J/cm3 was attained accompanied by excellent temperature stability (variation ≤±5% between 30 and 120°C). The current results show that the developed dielectric ceramics can be used in pulse capacitor devices for energy storage.

Insights into the correlation between strain and electrostrictive coefficient of potassium sodium niobate based ceramics from relaxor structure

Eco-friendly (K, Na)NbO3 (KNN)-based electrostrictive materials have attracted increasing attention as potential candidates for high-precision displacement actuators. Although a series of breakthroughs have increased the electrostrictive coefficient of KNN-based materials with relaxor behaviour (Q33 > 0.0450 m4/C2), the electrostrictive strain is still low (<0.1%), making the improvement of the electrostrictive strain a crucial next step. Here, a KNN-based relaxor ceramic of 0.96K0.48Na0.52Nb1-xSbxO3-0.04Bi0.5Na0.5ZrO3-0.3%Fe2O3 (KNNSx-BNZ) was designed to simultaneously achieve high electrostrictive strain and Q33. The phase structure transformed from the T phase to the C phase with increasing Sb concentration, which also introduced fine grains and domains. A high electrostrictive strain (∼0.102%) and Q33 (∼0.0461 m4/C2) were obtained at x = 0.09 through a small adjustment of the structure of the relaxor, while an electrostrictive strain with low hysteresis (<10.5%) and an outstanding temperature stability (≥95%) were achieved in the broadened temperature range of 20–180 °C, representing properties superior to those of previous KNN-based and typical PZT-based materials. Our results will help researchers understand how to balance the strain and electrostrictive coefficient in lead-free materials, and thereby contribute toward accelerating the application of KNN-based electrostrictive materials in actuators.

Сегнетоэлектрические полимеры с улучшенными характеристиками

This article offers a short overview of the unique properties of PVDF-based electroactive polymers and their applications. Ferroelectric materials are widely used in modern electronics. Relaxor-ferroelectric terpolymers are multifunctional materials with high electrostrictive strain which, in turn, leads to large actuation capability. The terpolymer with clorofluoroethylene shows relaxor-ferroelectric behavior with vanishing hysteresis effect but considerably higher polarization. Therefore, such material is a potential candidate for energy-storage devices (supercapacitors).

High electrostrictive strain in lead-free relaxors near the morphotropic phase boundary

Thanks to its small hysteresis, large electrostrictive strain in relaxor ferroelectrics is superior than piezoelectric strain for applications in precision microactuators. Although relaxor ferroelectrics exhibit the largest electrostrictive strain in ceramics, the magnitude of the strain is limited to ∼0.20% at room temperature due to the large amount of non-ferroelectric defects existing in relaxors. In this work, we develop a relaxor with a morphotropic phase boundary (MPB) by doping a rhombohedral (R3m) ferroelectric BaZr0.2Ti0.8O3 into a tetragonal (P4 mm) ferroelectric 0.89Bi0.5Na0.5TiO3-0.11BaTiO3. A high electrostrictive strain of 0.27% is achieved at room temperature in the relaxor sample. Experimental results illustrate that the composition is near the MPB and exhibits the existence of nanodomains, favoring the achievement of high electrostrictive strain. Moreover, phase field simulations show that the high electrostrictive strain obtained at this composition originates from the low defect fields needed to induce relaxor as a result of small polarization anisotropy at the phase boundary as compared to conventional relaxors away from phase boundaries. Our work provides a new design strategy for the next generation of high-performance ferroelectric relaxors.

BaTiO3 nanowires-induced phase transition and thermally stable strain in (Bi0.5Na0.5)TiO3 piezoelectric ceramics

Environment-friendly lead-free piezoceramics with high strain response and extremely excellent stability in a wide operating temperature range are critically important in practical actuator applications. Here, we develop a new strategy to tune the electrostrictive strain behavior in Bi 0.5 Na 0.5 TiO 3 (BNT)-based ceramics via using high aspect ratio BaTiO 3 nanowires (BT NWs) as a modifier. The addition of BT NWs generates a crossover from a typical ferroelectric (BT conventional spherical particles) to a complete ergodic relaxor (ER) phase at ambient temperature, accompanied by a large electrostrictive strain of ∼0.17% with d 33 *( S max / E max ) = 284 pm/V. Such a high electrostrictive strain is extremely thermally stable with only <7% fluctuation from 27 °C to 120 °C. In addition, the BT NWs-modified ceramics also exhibit acceptable fatigue endurance (<30% up to 10 5 cycles) and frequency dependence (<20% at 10Hz–100Hz). These achieved exceptional performances can be ascribed to the BT NWs-driven complete ER phase at room temperature. The findings of this study can inspire enhanced interest in nanowires as a viable modifier to BNT-based materials due to promising potential for practical actuator applications in a wide temperature range.

High dielectric permittivity and electrostrictive strain in a wide temperature range in relaxor ferroelectric (1-x)[Pb(Mg1/3Nb2/3)O3-PbTiO3]-xBa(Zn1/3Nb2/3)O3 solid solutions

High electric field-induced strain with ultralow hysteresis, which is often generated based on electrostrictive effects in ferroelectric materials, is highly desired due to its potential applications in high-precision displacement actuators. In this paper, (1-x)[Pb(Mg1/3Nb2/3)O3-PbTiO3]-xBa(Zn1/3Nb2/3)O3 [(1-x)(PMN-PT)-xBZN] ceramics were fabricated by a solid-state reaction method. The effect of Ba(Zn1/3Nb2/3)O3 (BZN) content on dielectric and electrostrictive properties in relaxor ferroelectric PMN-PT solid solutions was investigated in detail by dielectric spectra, polarization-electric field (P-E) hysteresis loops and strain-electric field (S-E) curves. With an increasing BZN content, the temperature stability of the dielectric permittivity of (1-x)(PMN-PT)-xBZN is improved due to the formation of two coexistent phases. A high electrostrictive strain (~0.17% at 60 kV/cm) with an ultralow hysteresis (<10%) characteristic is obtained in a composition where x = 0.1725. The strain versus polarization (S-P) curves measured from 30 °C to 130 °C can be well fitted based on a quadratic relation, suggesting the dominating role of the electrostrictive effect. The longitudinal electrostrictive coefficient Q33 for this system ranges from 0.0254 m4/C2 to 0.0318 m4/C2. Our results suggest that (1-x)(PMN-PT)-xBZN ferroelectric ceramics are potential candidates for applications in capacitors and high-precision displacement actuators.

High electrostrictive effect in La3+-doped Ba(Zr0.2Ti0.8)O3 lead-free ferroelectrics

Perovskite ferroelectric ceramics with Tm (temperature corresponding to maximum dielectric permittivity ε′) around room temperature and high electrostrictive coefficient Q33 are of interest to the applications in high-precision actuators, since low-hysteresis/non-hysteresis and high strain response can be generated in these materials based on a purely electrostrictive effect. In this work, undoped Ba(Zr0.2Ti0.8)O3 (BZT) and La3+-doped Ba(Zr0.2Ti0.8)O3 (BLZT) lead-free ferroelectrics were synthesized by solid state reaction method. Their dielectric and ferroelectric properties were investigated systematically with an emphasis on electrostrictive effect. With respect to increase of La3+ content from 0 to 1%, the Tm of BLZT decreases from 44.5 °C to 14.6 °C, and the diffuseness degree γ increases from 1.814 to 1.993. A conductive mechanism, which is prominent in undoped BZT, is inhibited drastically by introducing the La3+ into BZT. A high electrostrictive strain of 0.08% and a low hysteresis η (<10%) are obtained simultaneously in x = 0.25% composition at room temperature. The Q33 ranges from 0.0377 m4/C2 and 0.0537 m4/C2. This work not only reports a high electrostrictive effect in BLZT ferroelectrics, but also provides BLZT ceramics with a potential application in high-precision actuators.

A microstructure-based approach to modeling electrostriction that accounts for variability in spatial locations of domains

The discovery of polyvinylidene fluoride (PVDF) based family of relaxor ferroelectric (RFE) polymers has attracted attention due to their high electrostrictive strain and relatively low hysteresis loss. These RFE polymers exhibit complex microstructures containing both crystalline domains and amorphous domains; the interactions of the crystalline domains drive the electrostrictive behavior of these EAPs, while the amorphous domains dictate the mechanical behavior of the materials. Furthermore, the crystalline domains are spatially and orientationally distributed across the amorphous medium, further complicating the morphology of RFE polymers. Although a number of studies have focused on experimental and computational investigation of the interaction among different crystalline phases of this family of RFE, electrostriction models that represent the variabilities in the microstructure of biphasic RFE polymers are lacking. The proposed model aims to link the semicrystalline microstructure to the observed electromechanical coupling. An energy density function is constructed for a representative volume element (RVE) of the EAP, including a term for each phase, crystalline and amorphous. The interaction of the crystalline domains is based on the Coulomb interaction energy between a pair of dipoles. The responses of the amorphous domains are predicted by a modified hyperelastic stress–stretch eight-chain model. The total free energy is then analyzed under constitutive laws for an isothermal electromechanical deformation to determine the stresses generated in the RVE. The strain versus electric field, i.e. the electrostriction, relationship is calculated from a self-equilibrium condition of the Cauchy stress. The microstructure of the material is taken into account by applying the dipolar energy to a semicrystalline network model, in which a dipole that represents a crystalline domain is surrounded by an amorphous medium. The semicrystalline RVE experiences interactions with neighboring crystallites, which drives the electrostriction of the material. Two basic cases of the semicrystalline network model are explored to study the effects of spatial variation of crystalline domain locations relative to each other. Furthermore, higher fidelity descriptions of spatial location are introduced through the addition of a probability density function (PDF) of dipoles around a central dipole. Comparing the model to experimental results from the literature allows best-fit determination of the model parameters describing the PDF, e.g. aspects of microstructure, itself. These results, which agree well with experimental data, imply that the model has an ability to infer key information about the microstructure of the material by fitting the distribution of dipoles with a single adjustable parameter. The model is unique in that its descriptions of the crystalline domains is amenable to direct measurement by spectroscopic scattering techniques. Consequently, adjustable parameters in the model are linked to physical characteristics that are quantifiable, such as magnitudes of dipole moments and spatial distribution parameters.The model may also be used to elucidate aspects of network morphology using best fit of these physically meaningful adjustable parameters to experimental data, possibly providing a link between processing-structure-property relationships for future researchers.

High electrostrictive strain induced by defect dipoles in acceptor-doped (K0.5Na0.5)NbO3 ceramics

Acceptor doping is an efficient method to improve ferroelectric material performance through the formation of defect dipoles. Here, a high electrostrictive strain of 0.16–0.19%, and large of >300 pm V−1 are obtained in CuO-doped (K0.5Na0.5)NbO3 ceramics. We analyzed the orientation relationship and the interaction between defect dipole polarization (Pd) along 〈0 0 1〉 orientation and spontaneous polarization (Ps) parallel to 〈1 1 0〉 in orthorhombic (K0.5Na0.5)NbO3. Thus, a ‘coupling effect’ mechanism was suggested to explain how the Pd and Ps can work together to contribute to the electrostrictive strains in this lead-free piezoelectric ceramic.

Phase diagram and electrostrictive effect in BNT-based ceramics

In this work, phase diagram for the (Bi0.5Na0.5)TiO3–KNbO3–SrTiO3 ternary system has been constructed and analyzed based on macroscopic properties and structure analysis and pseudocubic (0.92−x)BNT–0.08KN–xST (0≤x≤0.07) ceramics have been fabricated and investigated. A morphotropic phase boundary between the ferroelectric rhombohedral and relaxor pseudocubic phases at around critical composition was proposed, resulting in large strain response. The polarization hysteresis loops, strain hysteresis loops and S–P2 curves demonstrate electrostrictive behavior of all studied samples. A very high electrostrictive strain (~0.148%) with a high electrostrictive coefficient Q11 of 0.0236m4C−2 is obtained for the 0.90BNT–0.08KN–0.02ST composition, which was entirely comparable to the well-known electrostrictive material Pb(Mg1/3Nb2/3 )O3 and attributed to the formation of relaxor pseudocubic phase developed by the SrTiO3 substitution. Meanwhile, the electrostrictive coefficient exhibited a highly temperature-insensitive behavior, indicating that the investigated system is suitable for high-precision positioning devices and solid-state actuators.

Growth of (Na0.5Bi0.5)TiO3-Ba(Ti1-xZrx)O3 single crystals by solid state single crystal growth

Single crystals of (Na0.5Bi0.5)TiO3-Ba(Ti1-xZrx)O3 are of interest for use in actuator applications due to their high electrostrictive strain. Growth of single crystals by traditional techniques requires specialised equipment and it is difficult to control chemical homogeneity in crystals with complex composition. In the present work, single crystals of 0.95(Na0.5Bi0.5)TiO3-0.05Ba(Ti1-xZrx)O3 have been grown for the first time by the solid state single crystal growth technique. -oriented SrTiO3 seed crystals were encased in powders of 0.95(Na0.5Bi0.5)TiO3-0.05Ba(Ti1-xZrx)O3 (x = 0.00, 0.01, 0.05, 0.10) and sintered. Single crystals of 0.95(Na0.5Bi0.5)TiO3-0.05Ba(Ti1-xZrx)O3 grew epitaxially on the seed crystals. Doping with Zr drastically reduced both the single crystal and matrix grain growth rates. Electron Probe Micro Analysis revealed the single crystals to be Na and Bi-deficient. Micro-Raman scattering showed that the single crystals and matrix grains have the same rhombohedral (Na0.5Bi0.5)TiO3 structure. The Raman modes of both single crystal and matrix broaden with increasing Zr content.

Large Electrostrictive Strain in (Bi0.5Na0.5)TiO3–BaTiO3–(Sr0.7Bi0.2)TiO3 Solid Solutions

Relaxor ferroelectrics (0.94 − x)(Bi0.5Na0.5)TiO3–0.06BaTiO3−x(Sr0.7Bi0.2□0.1)TiO3 (BNT–BT–xSBT) (0 ≤ x ≤ 0.5), were prepared by a solid‐state reaction process, and their structures were characterized by the transmission electron microscopy and Raman spectroscopy. The BNT–BT–0.3SBT has a very high electrostrictive strain S = 0.152% with hysteresis‐free behavior, much more than the reported S in other ferroelectrics. S–P2 profiles perfectly follow the quadratic relation, which indicates a purely electrostrictive effect with a high electrostrictive coefficient (Q11) of 0.0297 m4/C2. Even, its Q11 keeps at a high level in the temperature range from ambient temperature to 180°C. The field‐induced large electrostrictive strain of BNT–BT–0.3SBT was attributed to the existence of ferroelectric nanodomains.

Review on the properties of the ferrorelaxor polymers and some new recent developments

It has been found that by introducing defects into the P(VDF-TrFE) copolymers, it is possible to convert the polymer from a normal ferroelectric to a relaxor ferroelectric. A new class of ferroelectric polymers, i.e., the terpolymers of P(VDF-TrFE-CFE) or of P(VDF-TrFE-CTFE), was developed from the normal ferroelectric PVDF-TrFE polymer by employing proper defect modifications which eliminate detrimental effects associated with a normal first order F–P transition while maintaining high material responses. Relevant studies show that this class of electroactive polymers offers unique properties in comparison with other ferroelectric polymers. The syntheses of these relaxor ferroelectric polymers have been done by a combination of the suspension polymerization process and an oxygen-activated initiator at a temperature of 40°C. Films from cast solution can be made in different lengths and thicknesses. Stretching of these films increases the performance as well as the mechanical properties. These relaxor-ferroelectric terpolymers P(VDF-TrFE-CFE), P(VDF-TrFE-CTFE) are multifunctional, i.e., electrostrictive material, dielectric for electric energy storage. The terpolymer exhibits high electrostrictive strain (>7%) with relatively high modulus (>0.4 GPa). Examples of devices applications using unimorphe systems are presented. Micropump and Optical device concerning a liquid-filled varifocal lens on a chip are described.

Relaxor fluorinated polymers: novel applications and recent developments

It has been found that by introducing defects into the P(VDF-TrFE) copolymers, it is possible to convert the polymer from a normal ferroelectric to a relaxor ferroelectric. A new class of ferroelectric polymers, i.e., the terpolymers of P(VDF-TrFE-CFE) or of P(VDF-TrFE- CTFE), was developed from the normal ferroelectric PVDF-TrFE polymer by employing proper defect modifications which eliminate detrimental effects associated with a normal first order F-P transition while maintaining high material responses. Relevant studies show that this class of electroactive polymers offers unique properties in comparison with other ferroelectric polymers. The syntheses of these relaxor ferroelectric polymers have been done by a combination of the suspension polymerization process and an oxygen-activated initiator at a temperature of 40 °C. Films from cast solution can be made in different length and thicknesses. Stretching of these films increases the performance as well as the mechanical properties. These relaxor-ferroelectric terpolymers P(VDF-TrFE-CFE), P(VDF-TrFE-CTFE) are multifunctional i.e. electrostrictive material, dielectric for electric energy storage. The terpolymer exhibits high electrostrictive strain (>7%) with relatively high modulus (>0.4GPa) and high electrocalorific effect. Dielectric polymers with high dipole density have the potential to achieve very high energy density. Examples of devices applications using unimorphe systems are presented. Micropump and Optical device concerning a liquid-filled varifocal lens on a chip are described.

Structural and ferroelectric response in vinylidene fluoride/trifluoroethylene/hexafluoropropylene terpolymers

Poly(vinylidene fluoride/trifluoroethylene/hexafluoropropylene) terpolymers were synthesized by bulk polymerization process at ambient temperature based on alkyl borane/oxygen initiator. The ferroelectric and dielectric properties were investigated and compared with those of poly(vinylidene fluoride/trifluoroethylene) copolymer. The DSC, X-ray and FT-IR results suggest that the third comonomer in the polymer chain breaks the large polar domains into smaller domain size and reduces the crystallinity of terpolymer. As a result, both the ferroelectric–paraelectric phase transition and melting process take place at lower temperature. The smaller domain makes the dipoles reversal at lower electric field and reduces the polarization hysteresis as well as polarization level. High electrostrictive strain (2.5%) was obtained at low electric field for terpolymer with small quantity of HFP. The polarization and dielectric behaviors imply that the terpolymer is a typical ferroelectric relaxor. The terpolymer also shows higher room temperature dielectric constant than that of copolymer due to the lower phase-transition temperature.

Fabrication of an optical grating using high electrostrictive strain polymer as a template

This study introduces a simple and inexpensive method of fabrication of optical microgratings, by using a P(VDF?TrFE?CFE) (that is, poly(vinylidene fluoride?trifluoroethylene)?chlorofluoroethylene) terpolymer with high electrostrictive strain as a template. When an electric field was applied to the terpolymer, which has a patterned electrode, a grating formed on the surface. Epoxy was poured onto the grating of the terpolymer template and cured to produce an optical grating. A 22% efficiency of the first-order diffraction was achieved by fabricating an epoxy micrograting in which the terpolymer template was 13??m thick with electrode/gap/electrode dimensions of 5??m/15??m/5??m.

Recent advances in highly electrostrictive P(VDF-TrFE-CFE) terpolymers

Ferroelectric materials are intrinsically multifunctional and have found a broad range of applications. A new class of semicrystalline terpolymers comprising vinylidene fluoride (VDF), trifluoroethylene (TrFE), and 1,1-chlorofluoroethylene (CFE), were prepared at Institut de Saint-Louis (ISL) via a suspension polymerization process. Relevant studies and results show that this class of electroactive polymers offers unique properties in comparison with other ferroelectric polymers. The terpolymer exhibits high electrostrictive strain (>7%) with relatively high modulus (>0.3GPa). It has been also observed that the large electrostrictive strain is nearly constant in the temperature range from 20 to 80 degC. The high room temperature relative dielectric constant (~50), which is the highest among all the known polymers), high induced polarization (~0.05 C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and high electric breakdown field (>400 MV/m) lead to very high volume efficiency for the electric energy storage operated under high voltage (~10 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> )

Recent advances in highly electrostrictive P(VDF-TrFE-CFE) terpolymers

Ferroelectric materials are intrinsically multifunctional and have found a broad range of applications. A new class of semicrystalline terpolymers comprising vinylidene fluoride (VDF), trifluoroethylene (TrFE), and 1,1-chlorofluoroethylene (CFE), were prepared at Institut de Saint-Louis (ISL) via a suspension polymerization process. Relevant studies and results show that this class of electroactive polymers offers unique properties in comparison with other ferroelectric polymers. The terpolymer exhibits high electrostrictive strain (>7%) with relatively high modulus (>0.3GPa). It has been also observed that the large electrostrictive strain is nearly constant in the temperature range from 20 to 80 degC. The high room temperature relative dielectric constant (~50), which is the highest among all the known polymers), high induced polarization (~0.05 C/m2), and high electric breakdown field (>400 MV/m) lead to very high volume efficiency for the electric energy storage operated under high voltage (~10 J/cm3)

High, Purely Electrostrictive Strain in Lead‐Free Dielectrics

A high electrostrictive strain (∼0.1%) with hysteresis-free behavior is observed in (Sr,Na,Bi)TiO3 solid solutions. Its strain versus polarization (P) completely follows the quadratic relation (see Figure), indicating a purely electrostrictive effect with an electrostrictive coefficient Q11 of 0.02 m4 C–2. These properties of this environmentally friendly lead-free material are comparable with those of the currently used lead-containing materials.

Large electrostriction near the solubility limit in BaTiO3–CaTiO3 ceramics

This study prepared (1−x)BaTiO3–xCaTiO3 (x=0.20–1.0) ceramics. Their structural and electric properties were analyzed. High electrostrictive strain of 0.22%, higher by 157% as compared to BaTiO3 ceramic, was obtained near the solubility limit in the side of composite (x=0.23), which is a diphasic ceramic composed of a ferroelectric tetragonal Ba0.8Ca0.2TiO3 solid solution and a normal dielectric orthorhombic Ba0.07Ca0.93TiO3 solid solution. This enhanced electrostriction resulted from the coupling of the large ionic polarization in Ba0.07Ca0.93TiO3 with the non-180° domains in Ba0.8Ca0.2TiO3 during the external electric field exertion.