Electrostrictive Strain Research Articles

Electrostrictive Properties of Pr-Doped BaTiO3–CaTiO3 Ceramics

Pr-doped (1-x)BaTiO3–xCaTiO3 (x=0.20–1.0) ceramics were prepared by a solid-state reaction technique. Their structures were found to be a pure tetragonal phase for x≤0.23, coexisting tetragonal and orthorhombic phases for x=0.25 to 0.90, and a pure orthorhombic phase for x≥0.90, respectively. A large electrostrictive strain of 0.265%, 1.76 times that of BaTiO3 ceramics, was obtained near the solubility limit on the side of the composite (x=0.25), which is a diphasic ceramic composed of a ferroelectric tetragonal Ba0.77Ca0.23TiO3:Pr solid solution and a normal dielectric orthorhombic Ba0.1Ca0.9TiO3:Pr solid solution. The enhancement of electrostriction resulted from the doping effect and coupling of the large ionic polarization in Ba0.1Ca0.9TiO3:Pr with the non-180° domains in Ba0.77Ca0.23TiO3:Pr during the external electric field exertion.

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.

Electroactive polymer based microfluidic pump

A planar, valveless, microfluidic pump using electrostrictive poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymer as the actuator material is presented. P(VDF-TrFE) thick films having a large electrostrictive strain ∼5–7% and high elastic energy density of 1 J/cm 3 have been used in a unimorph diaphragm actuator configuration. The microfluidic pump was realized by integrating a nozzle/diffuser type fluidic mechanical-diode structure with the polymer microactuator. The P(VDF-TrFE) unimorph diaphragm actuator, 80 μm thick and 2.2 mm × 2.2 mm in lateral dimensions, showed an actuation deflection of 80 μm for an applied electric field of 90 MV/m. The microfluidic pump could pump methanol at a flow rate of 25 μl/min at 63 Hz with a backpressure of 350 Pa. The flow rate of this pump could be easily controlled by external electrical field. Two different sizes of nozzle/diffuser elements were studied and the pumping efficiency of these structures is 11 and 16%, respectively.

Modification of the structure and properties of poly(vinylidene fluoride–trifluoroethylene) 56/44 mol % copolymer by a proton‐irradiation treatment

AbstractThe effects of high‐energy proton irradiation on the structure and properties of 56/44 mol % poly(vinylidene fluoride–trifluoroethylene) copolymer were studied with differential scanning calorimetry (DSC), X‐ray diffraction (XRD), relative permittivity, and polarization hysteresis measurements. Copolymer films prepared by hot compression molding were irradiated with a broad range of proton dosages (10–107 Mrad) at room temperature. The DSC results showed that the ferroelectric transition was strongly affected by the proton dosages. The XRD data indicated the reduction of polar ordering in the copolymer by the proton‐irradiation treatment. From the relative permittivity and polarization behavior, the copolymer film was found to be converted from a normal ferroelectric material to a relaxor ferroelectric material as the proton dosage was increased to 50 Mrad. The electrostrictive coefficient of the 56/44 mol % copolymer was enhanced after irradiation, and the optimized proton dosage for attaining the highest electrostrictive strain response was determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2334–2339, 2005

Electrostriction in single-walled carbon nanotubes

Single-walled carbon nanotube (SWCNT) is an electrostrictive material. A significant electrostriction strain was found in semi-conductor SWCNT as a consequence of its carbon atoms’ vibration under an applied electric field. The use of the conductive atomic force microscopy (AFM) combined with lock-in amplifier operating at the second harmonic (2 ω), facilitated the determination of the experimental electrostriction coefficient ( C e) of about 2 nm 2 V −2 which is not negligible compared to other dielectric materials like polymers, quartz or inorganic. Regarding percentage, this electrostriction strain represents 2.6% under an applied electric field of 160 V μm −1. This finding may the nanometer size, the stiffness and the intrinsic characteristics of the SWCNTs would enable them as a potential candidate for nano-electro-mechanical-system (NEMS) technology, nanopositioning or in ultrasound vibrations applications.

Electrostriction of lead zirconate titanate/polyurethane composites

Electrostriction of a ferroelectric inclusion/nonferroelectric matrix composite system was studied. The samples were prepared by blending the lead zirconate titanate (PZT) particles with the thermoplastic polyurethane through extrusion and subsequently by hot pressing. Quasistatic cyclic electric fields were applied across the samples while strains and currents were monitored simultaneously. It was found that the electrostriction of the composites depended on the applied electric field in a hysteretic manner. In particular at the high-field regime, the samples exhibited a reversal in the electrostrictive strain. This switching effect occurred at a critical field which was inversely proportional to the PZT content. An associated increase in the displacement current with the critical field was also observed. It indicates that the switching in strain of the composites was mainly due to the flipping of the PZT dipoles in the nonferroelectric polymer matrix. A model was developed for describing the electrostriction behavior of this composite system and the calculated results are comparable to the experimental curves. The success of this theoretical model encourages its application further to the ferroelectric–ferroelectric composite systems.

X-ray imaging investigation of periodically electroded rubidium titanyl arsenate, RbTiOAsO4, under an applied electric field

The behaviour of a (001) slice of initially single-domain rubidium titanyl arsenate (RbTiOAsO4, RTA) crystal, when prepared with a periodic Ag electrode of period 38 µm, as for periodic poling in nonlinear optics, is investigated for applied voltages of up to ±1.5 kV. The method of investigation is by synchrotron x-ray section topography with electric fields applied in situ, while under white-beam x-ray illumination at the ID19 topography beamline of the ESRF, Grenoble. An increasing expansion of the width of section topographs is observed with increasing voltage resulting from a corresponding bending of the lattice planes in the near-surface region, with angles ranging between 4–200 µrads. This behaviour is explained by the formation of a Schottky barrier, which results from a semiconductor–metal contact interaction between RTA and the Ag film, in the near-surface region beneath the high voltage electrode. This restricts the depth of the electric field to a near-surface depletion layer. The actual bending of the planes is by the electrostrictive strain that acts only in the depletion layer where the field is non-zero.

Large electrostrictive strain at gigahertz frequencies in a polymer nanoactuator: Computational device design

Using molecular dynamics with a first-principles-based force field (denoted MSXX), we show that large electrostrictive strains (∼5%) at extremely high frequencies (over ∼109Hz) can be achieved in a poly(vinylidene-fluoride) nanoactuator if the packing density of the polymer chains is chosen appropriately. We control the packing density by assembling the polymer chains on a silicon ⟨111⟩ surface with one-half coverage. Under these conditions, the equilibrium, zero electric field conformation of the polymer contains a combination of gauche and trans bonds. This structure can be transformed to an all-T conformation by applying an external electric field. Such molecular transformation is accompanied by a large deformation in the direction of the polymer chains. The device shows typical electrostrictive behavior with strain proportional to the square of the polarization.

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.

Deformation mechanisms of electrostrictive graft elastomer

The electrostrictive graft elastomer is a new type of electroactive polymer. Recentlydeveloped by NASA, it consists of flexible backbone chains, each with side chains, calledgrafts. Neighboring backbone grafts physically cross-link and form crystal units. Theflexible backbone chain and the crystal graft unit consist of polarized monomers, whichcontain atoms with electric partial charges, generating dipole moments. When theelastomer is placed into an electric field, external rotating moments are applied to thedipole moment. This stimulates electrostrictive strain in the graft elastomer. In this paper,the deformation of the elastomer under the action of an electric field is explained by meansof two dominant mechanisms: crystal graft unit rotation and backbone chain reorientation.A two-dimensional computational model is established to analyze the deformation.

Electro-optical response of the ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

The electro-optical (EO) properties of the ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer were investigated in the wavelength region from 3 to 5 μm. A large Kerr effect was observed in which a refractive index change of −2.6% can be induced under an electric field of 80 V/μm. When combined with the electrostrictive strain, the terpolymer film exhibits a total −5.6% optical path-length change under a field of 80 V/μm. Calculations based on density functional theory suggest that such a large EO effect was caused mainly by the reorientation of the C–F dipoles under external field in the crystalline region. Furthermore, the results support the notion that in the ferroelectric relaxor terpolymer, there exist nanopolar regions that undergo reorientation under external field and generate the observed electrostrictive strain and EO responses.

Pb(Mg1/3Nb2/3)O3and (1 - x)Pb(Mg1/3Nb2/3)O3- xPbTiO3Relaxor Ferroelectric Thick Films: Processing and Electrical Characterization

The lead magnesium niobate [Pb(Mg1/3Nb2/3)O3 or PMN], and its solid solutions with lead titanate (PbTiO3 or PT), are of great interest because of their high electromechanical properties. At large PMN content, these materials exhibit relaxor characteristics with large electrostrictive strains and a large permittivity, while compositions near the morphotropic phase boundary present very interesting piezoelectric properties. So far, properties of these materials in ceramic, thin film and single-crystal form have been investigated. In this paper, we report on preparation and properties of pyrochlore free PMN and 0.65PMN-0.35PT thick films (thickness = 10 to 20 μm). The films were prepared from ethyl cellulose ink by screen printing on alumina substrate. The influence of various parameters, such as powder characteristics, inks formulation and films sintering conditions, on films densification are discussed. The dielectric and electromechanical properties of the films were examined. Relaxor-like behaviour was clearly demonstrated in PMN films. The maximum relative permittivity for PMN film was 10000 (at 0.1 kHz), which is lower than in bulk ceramics (17800 at 0.1 kHz) prepared under the same conditions. For 0.65PMN-0.35PT, the maximum relative permittivity was around 15500 against 24000 in the bulk. Several parameters, which might be responsible for the lower permittivity, are discussed. Poled 0.65PMN-0.35PT thick films exhibit relatively large piezoelectric response (d 33 up to 200 pm/V) and unipolar strains approaching 0.1%, making these films of interest for various actuator and transducer applications.

Study of the structure and electrostrictive property of proton-irradiated P(VDF-TrFE) 56/44 mol% copolymer

High-energy proton (3 MeV) irradiation with dosages ranging from 43 to 200 Mrad have been carried out to investigate the potential for modifying both the structure and property of vinylidene fluoride-trifluoroethylene 56/44 mol% copolymer. The structural and transitional behavior of the irradiated copolymer was studied by X-ray diffraction and differential scanning calorimetry. The polarization hysteresis, relative permittivity properties and electrostrictive strain response of these copolymers were also measured. It was found that the ferroelectric copolymer could be successfully converted to a relaxor at a low proton dosage of about 75 Mrad at ambient temperature. A slim polarization hysteresis loop and a frequency dispersion of the relative permittivity observed in the irradiated copolymer imply that the high-energy protons break up the coherent polarization domains in the ferroelectric copolymer into nanosized regions. In addition, the irradiation leads to a significant change in the ferroelectric-to-paraelectric phase transition behavior. X-ray diffraction measurements show that the crystalline region in the copolymer is converted into a nonpolar phase upon irradiation, and the lattice spacing increases significantly. The electric field induced phase transformation of the nanosized regions between the nonpolar and polar phase leads to a high electrostrictive strain observed in the irradiated copolymer.

Poly(vinylidene fluoride-trifluoroethylene) based high performance electroactive polymers

Making use of defects modification to P(VDF-TrFE) via either high energy electron irradiation treatment or copolymerizing VDF-TrFE with a small amount of chlorinated monomer to form a random terpolymer, we demonstrate that high electromechanical responses can be realized in P(VDF-TrFE) based polymers. It will be shown that in the stretched and irradiated 68/32 mol% copolymer, a transverse strain of 4.5% and a transverse electromechanical coupling factor k/sub 31/ of 0.65 can be induced under a field of 85 MV/m. In addition, the irradiated copolymer also exhibits a high elastic energy density, /spl sim/ 1 J/cm/sup 3/. For PVDF based terpolymers such as P(VDF-TrFE-CFE) terpolymer (CFE: chlorofluoroethylene), an electrostrictive strain of more than 7% can be obtained. To elucidate the microstructure changes due to the defects modification in P(VDF-TrFE) based polymers, synchrotron X-ray measurement was carried out on the irradiated copolymers and the results show that, the irradiation converts the polar-phase into a nonpolar phase. In addition, X-ray date show that the polar-phase can be induced, at the expense of the nonpolar phase, by external fields, confirming that the field induced conformation change is responsible for the observed high electromechanical responses. Although the modified PVDF based polymer exhibits the highest room temperature dielectric constant (60 versus below 10), it is still far below those in the inorganic materials. Experimental results show that by using delocalized electrons in conjugated bonds an all-organic composite with a dielectric constant more than 400 can be achieved. As a result, a strain of near 2% with an elastic energy density higher than 0.1 J/cm/sup 3/ can be induced under a low applied field of 13 V//spl mu/m. The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa.

Ferroelectric copolymers and terpolymers for electrostrictors: synthesis and properties

Semicrystalline terpolymers comprising vinylidene fluoride (VDF), trifluoroethylene (TrFE), and 1,1-chlorofluoroethylene (CFE), terpolymers were prepared via a suspension polymerization process. For two specific compositions, relevant relaxor properties as well as high dielectric permittivity have been observed. More importantly, very large electrostrictive strains ( /spl sim/ 7%) were achieved in these terpolymers.

Ferroelectric and Relaxor-Like Electromechanical Strain in BaTi1-xSnxO3 Ceramics

The electromechanical strain induced in BaTi1-xSnxO3 ceramics at room temperature is maximal for x ≈ 0.09. This results from the superposition of electrostrictive (relaxor-type) and ferroelectric strain contributions in this composition range.

Thermal and Electric Properties of P(VDF-TrFE) and P(VDF-CTFE) Copolymer Blends

ABSTRACTPVDF-based electroactive polymers (EAP) exhibit high electromechanical performance that is attractive for developing high performance actuators and sensors. In an effort to develop very inexpensive electroactive polymers, P(VDF-TrFE)/P(VDF-CTFE) copolymer blends are studied and reported. The structure, morphology, thermal transition and miscibility of the blend system were investigated by DSC and X-ray diffraction. It is found that the phase transition behavior of the blends can be significantly modified using thermal and mechanical treatmentss. The modified film exhibits high polarization response and low remanent polarization. More importantly, a high electrostrictive strain of 5% was observed in the treated blends. Combined with Young's modulus, the results show that the copolymer blends have a electromechanical coupling factor and energy density comparable or even higher than the irradiated P(VDF-TrFE) copolymers.

Solid-like dynamics in ultrathin films of polymeric liquids

In this letter, we demonstrate that, at mesoscales, nonferroelectric liquid films of poly(dimethyl siloxane) exhibit significant electrostriction not present in the corresponding bulk state. Remarkably, the observed electrostrictive effect has a response time <20 μs in contrast to >5 ms recorded in conventional bulk (ferroelectric) polymers. The emergence of this fast electrostrictive strain in thin films is explained in terms of the amalgamation of two contrasting dynamic features—the influence of a highly mobile, viscous layer (at the air/film interface) on the less-mobile, but fast responding, solid-like layer at the film/substrate interface. The effect is observed for thickness below 200 nm.

Micromechanics of ferroelectric polymer-based electrostrictive composites

Electrostriction refers to the strain induced in a dielectric by electric polarization, which is usually very small for practical application. In this paper, we present a micromechanical analysis on the effective electrostriction of a ferroelectric polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] polymer-based composite, where the exact connections between the effective electrostrictive coefficients and effective elastic moduli are established, and numerical algorithm for the prediction of the effective electrostrictive coefficients of the composite in terms of its microstructural information is developed. From our calculations, enhanced electrostriction in the composite has been demonstrated, and optimal microstructure for electrostriction enhancement has been identified. Our analysis provides a mechanism for the electrostriction enhancement, where the electrostrictive strain several times higher than that of polymer matrix can be obtained, if the microstructure of the composites can be carefully tailored.

Phase transition induced by thermal and electric fields in electron-irradiated poly (vinylidene fluoride-trifluoroethylene) copolymers

The reversible transformations between the metastable paraelectric phase induced in irradiation and polar ferroelectric phase (FEP) during both applied external field and thermal cycling process, were observed experimentally. The transition induced by thermal is interpreted by the ferroelectric theory of first-order transition, and the other one induced by electric field is explained by Landau–Devonshire phase transition theory. It is useful to elucidate the microscopic mechanism involved, and this might also be the most possible microscopic interpretation for large electrostrictive strain in these copolymers.