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We present a molecular dynamics simulation method including x‐ray diffractometer pattern calculation, mean square displacement (MSD), and nonbonding energy distribution (NED) to disclose the dependencies of condensed structure on its crystalline process of the poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) films. For comparison, the P(VDF‐TrFE) solution is casted into the films, and followed that different thermal processes are performed to fabricate the crystalline states of the films. Simulation and experimental results have good consistency, indicating that high temperature annealing can effectively promote all‐trans β phase in the crystal region of P(VDF‐TrFE). As such, P(VDF‐TrFE) 80/20 mol% annealing at 140°C shows a higher MSD (~27.5 Å2) and a faster reducing rate of NED than that of other films, contributing to a large maximum polarization (Ps) of ~15.5 μC cm−2, high a remnant polarization (Pr) of ~11.8 μC cm−2, and an attractive piezoelectric strain coefficient (d33) of −27.1 pC N−1 under 200 MV m−1, respectively, and providing a reference for the applications of P(VDF‐TrFE) in flexible sensors, actuators, transducers, and so forth. [ABSTRACT FROM AUTHOR]

A group of 0.65(Bi0.5Na0.5)TiO3 -0.35(Sr0.7+x + Bi0.2)TiO3 (BNT-S0.7+xBT) composite ceramic pellets are synthesized using a traditional solid sintering method, where a tunable x, the changeable volume of Sr, is to tailor energy storage through the adjustments of the A-site stoichiometry in BNT-S0.7+xBT. We find that a small excess of Sr2+ ions will result in an extensively tuning on the crystal grain size and even contribute to the A-site disorder and charge fluctuation of BNT-S0.7+xBT. As such, the BNT-S0.7+xBT exhibits a minimum average grain size and a highly compact crystal morphology, and thus, BNT-S0.75BT ceramic exhibits a high dielectric constant (εr) of about 5100 at 110 °C. Meanwhile, a relatively thin polarization–electric field (P–E) loop with a high maximum polarization of 42 μC/cm2 and a low remnant electric polarization of 5 μC/cm2 are obtained in a BNT-S0.75BT pellet under 100 kV/cm, corresponding to an energy density of 0.98 J cm−3 and a good η of 70.7%. Attractively, the maximum polarization (Pm) of BNT-S0.75BT ceramic at 25–100 °C hardly decreases, implying excellent temperature stability of polarization performances under high electric field of 100 kV/cm, which favors the energy storage of relaxor ferroelectric ceramics and is valuable to a supercapacitor serving at evaluated high temperature. [ABSTRACT FROM AUTHOR]

To clarify the influence of various molar concentrations of vinylidene fluoride (VDF) on the piezoelectric and acoustic emission (AE) reception performances of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] sensors, we systematically investigated the crystal structures and the dielectric and ferroelectric properties of P(VDF-TrFE) films with different compositions of VDF and TrFE monomers and found that low proportion (<30 mol%) TrFE as a wedge inserted into molecular chains of P(VDF-TrFE) will not only improve the fraction of regular β-phase crystal grains but also decrease the dielectric constant (εr) of these copolymers, which favors the piezoelectric voltage coefficient (g33) of this P(VDF-TrFE) film. As such, a considerable remanent electric polarization (Pr ~ 11.4 μC cm2) under 200 MV/m and a large piezoelectric coefficient (d33 ~ -25 pC/N) are obtained in P(VDF-TrFE) 80/20-mol% films. It is worth noting that a sensor made from P(VDF-TrFE) 80/20 mol% shows an attractive AE reception property of approximately 84 dB, a high signal voltage of above 10 mV from time-domain analysis, and a large signal voltage of above 4 mV from frequency-domain analysis, which are close to standard lead zirconate titanate (PZT) sensors. Considering its unique characters of flexibility, no required stretching, easily shaped, having high thermal Faille temperatures (Tc ~ 135.7 ∘C), etc., P(VDF-TrFE) piezoelectric film is considered a promising material for sensors, actuators, and energy transfer units. [ABSTRACT FROM AUTHOR]

Different thermal treatments were used to obtain various crystal structures of hydrogenated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] films synthesized by an atom transfer radical chain transfer and controllable elimination reaction route. After analyzing the results of X-ray diffraction and differential scanning calorimeter, we found that these P(VDF-TrFE) samples possessed mixed crystal phases of \alpha , \beta , and \gamma with various compositions depending on the TrFE content and processing temperature, and this characteristic was also demonstrated by the dielectric temperature curves. After polarizing the P(VDF-TrFE) samples at different electric fields, the effect of crystal structure on their ferroelectric and piezoelectric properties was illustrated and conformed by field emission scanning electronic microscopy morphology, which was found that large TrFE content and high temperature processing were responsible for the large remnant polarization. As a result, the annealed P(VDF-TrFE) 80/20 mol% possessed a high remnant polarization of /cm2, a large piezoelectric value ( d_{33}= -25 pC/N), and a favorable electromechanical coupling factor ( k_{t}= 0.26$ ), providing a reliable method for the structure design and sample fabrication of this kind of copolymer aimed at the applications in piezoelectric sensors and actuators. [ABSTRACT FROM AUTHOR]

Thermal processing at various temperatures has been used to fabricate poly(vinylidene fluoride- co-trifluoroethylene) [P(VDF- co-TrFE)] films with varied crystalline properties in an attempt to improve their piezoelectric properties. Although the dielectric constant of the films annealed at higher temperature is smaller than that of cooled and quenched ones, it has been shown that the annealed films possess larger crystallinity and stacked lamellar crystal grain size. The ferroelectric domains deriving from crystal region in all the samples are effectively improved by hot polarization. As a result, the remnant polarizations ( Pr) and coercive electric field ( Ec) of the corresponding films are improved at a low frequency due to the response of dipoles in crystal phase, and the largest piezoelectric constant in the longitudinal thickness mode ( d33=−25 pC/N) is obtained in an annealed copolymer film. The results illustrate improving the crystal structure of P(VDF- co-TrFE) is an effective way to realize high electromechanical properties, which provides broadly applied scenery for this kind of copolymer in piezoelectric components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 [ABSTRACT FROM AUTHOR]