High Electrostrictive Strain Research Articles

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.

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.

Dielectric and Field-Induced Piezoelectric Responses in Electron-Irradiated Poly(Vinylidene Fluoride- Trifluoroethylene) Copolymer

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers were transformed into relaxor ferroelectric phase by high-energy electron irradiation. Temperature and frequency dependence of dielectric properties were investigated under dc bias field. The relaxor ferroelectric copolymers show high electrostrictive strain response (Q12 = 10 m4/C2) with an effective d31 = 180 pm/V at a field of 50 MV/m. Direct piezoelectric response of the relaxor ferroelectric copolymer can be tuned by dc bias, d31 is measured to be 116 pC/N at 40 MV/m bias field. Electromechanical coupling (k31 = 0.28 at 60 MV/m bias field) was significantly enhanced in the relaxor ferroelectric copolymers as compared to that in the normal ferroelectric P(VDF-TrFE) copolymers.

Design, fabrication, and performance of a flextensional transducer based on electrostrictive polyvinylidene fluoride-trifluoroethylene copolymer.

Taking advantage of the high electrostrictive strain and high elastic energy density of a newly developed electrostrictive polymer, modified poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] based polymers, a flex-tensional transducer was designed, and its performance was investigated. The flextensional transducer consists of a multilayer stack made of electrostrictive P(VDF-TrFE) polymer films and two flextensional shells fixed at the ends to the multilayer stack. Because of the large transverse strain level achievable in the electrostrictive polymer and the displacement amplification of the flextensional shells, a device of a few millimeters thick and lateral dimension about 30 mm x 25 mm can generate an axial displacement output of more than 1 mm. The unique flextensional configuration and the high elastic energy density of the active polymer also enable the device to offer high-load capability. As an underwater transducer, the device can be operated at frequencies below 1 kHz and still exhibit relatively high transmitting voltage response (TVR), very high source level (SL), and low mechanical quality factor (Qm).

High-performance micromachined unimorph actuators based on electrostrictive poly(vinylidene fluoride–trifluoroethylene) copolymer

We report on the performance of micromachined unimorph actuators [(polymer micromachined actuator PMAT)] based on the electrostrictive poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] copolymer. Because of the high electrostrictive strain and high elastic energy density (∼1 J/cm3) of the active polymer [the electrostrictive P(VDF–TrFE)], the PMAT exhibits a very high stroke level with high load capability and high displacement voltage ratio. In addition, the experimental data also demonstrate that the PMAT is capable of operating over a broad frequency range (>100 kHz). The PMAT performance was modeled and the agreement between the modeling results and experimental data confirms that the response of the PMAT indeed follows the design parameters.

Relaxor single crystals in the (Bi1/2Na1/2)1−xBaxZryTi1−yO3 system exhibiting high electrostrictive strain

Single crystals have been grown in the (Bi1/2Na1/2)1−xBaxZryTi1−yO3 perovskite system by a self-flux method over the range of compositions y=0.04 and x=0.06–0.012. Rhombohedral (x⩽0.08) and tetragonal phase (x⩾0.09) crystals have been obtained that do not show polarization or field-induced strain hysteresis characteristics of a ferroelectric. However, a frequency-dispersive dielectric response characteristic of a relaxor ferroelectric, and predominantly electrostrictive actuation, is observed across the range of compositions tested, with Q11=(2.8–3.3)×10−2 m4/C2. Due to induced polarizations that do not saturate at fields beyond 50 kV/cm, high electrostrictive strains are obtained. Rhombohedral phase crystals exhibit d33 up to 1180 pC/N and strains of S3=0.3% before electrical breakdown, while tetragonal phase crystals exhibit d33 up to 2000 pC/N and S3 up to 0.45% strain. These crystals show the highest electrostrictive strains yet reported for an inorganic compound. The unusually high electrostriction is discussed in relation to an energy landscape that allows ferroelastic and ferroelectric distortions to be simultaneously accessible at the nanometer scale.

Ferroelectric and electromechanical properties of poly(vinylidene-fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymer

This letter reports the ferroelectric and electromechanical properties of a class of ferroelectric polymer, poly(vinylidene-fluoride–trifluoroethylene–chlorotrifluoroethylene) terpolymer, which exhibits a slim polarization hysteresis loop and a high electrostrictive strain at room temperature. The dielectric and polarization behaviors of this terpolymer are typical of the ferroelectric relaxor. The x-ray and Fourier transform infrared results reveal that the random incorporation of bulky chlorotrifluoroethylene (CTFE) ter-monomers into polymer chains causes disordering of the ferroelectric phase. Furthermore, CTFE also acts as random defect fields which randomize the inter- and intrachain polar coupling, resulting in the observed ferroelectric relaxor behavior.

High Electromechanical Coupling Factor and Electrostrictive Strain over Broad Frequency Range in Electrostrictive Poly(vinylidene fluoride-trifluoroethylene) Copolymer Films

Electromechanical coupling factor is one of the most important parameters for measuring the performance of materials for electromechanical transduction applications. In this paper, we will show that a transverse electromechanical coupling factor k31 of more than 0.45 can be achieved in poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer under certain electron irradiation treatment conditions. In addition, the effective piezoelectric coefficients of the irradiated copolymer have been found to increase markedly in comparison to non-irradiated copolymers. Experimental evidences also indicate that the improved electrostrictive strains in irradiated copolymer films can be maintained over a broad frequency and temperature range.

Effect of electron irradiation on poly(vinylidene fluoride-trifluoroethylene) copolymers

Electrical field-induced strain response of electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer has been studied by a Mach–Zehnder type heterodyne interferometer in the frequency range of 3–9 kHz. The electrostrictive constant is calculated from the strain results, which is of the same order of magnitude as those obtained at 1 Hz by a bimorph-based strain sensor but at much lower electrical field. Changes in the dielectric property, phase transition behavior and crystal structure of the same copolymer have also been studied. The reversible solid–state transition between the polar and nonpolar phase in the crystalline regions of the copolymer driven by the external electric field is suggested to be responsible for the significant high electrostrictive strain of the electron-irradiated copolymer.

High electrostrictive strain under high mechanical stress in electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer

In this letter, we show that the electric field induced strain in the electron irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer can generate high strain even under a high mechanical stress. The observed change in strain with stress is due to the electrostrictive coupling of the local polarization with stress, and can be directly related to the change of the induced strain with temperature. The results indicate that the field induced strain observed in the films investigated is indeed from the local polarization regions in the material, and is electrostrictive in nature.

Temperature-stable high electrostrictive strain relaxer ferroelectric ceramics for servo-actuator applications

For servo-type actuator applications, temperature-stable high electric-field-induced-strain electrostrictive lead magnesium niobate (PMN)-based relaxer ferroelectric materials are needed. The synthesis technique of the PMN-based composition with 100% perovskite phase is described. The effects of dopants and processing technology on the dielectric properties and electrostrictive properties are discussed in detail.