Ferroelectric and piezoelectric properties of nylon 11/poly(vinylidene fluoride) bilaminate films

The ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF₂) bilaminate films, prepared by a co-melt-pressing method, is presented. The bilaminate films exhibit typical ferroelectric D-E hysteresis behavior with a remanent polarization, P_r, of about 75 mC/m², which is higher than the value of 52 mC/m² observed for PVF₂ or nylon 11 films measured under the same conditions. The coercive field, E_c, of the bilaminate films is ～ 78 MV/m, which is higher than that of either PVF₂ or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient, d₃₁, and the piezoelectric stress coefficient, e₃₁, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient, d₃₁, of 41 pC/N at room temperature, which is significantly higher than the PVF₂ films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C, d₃₁ of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF₂ (11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient, e₃₁, of the bilaminate films shows a value of 109 mC/m² at room temperature, almost twice that of the PVF₂ films (59 mC/m²) and about 18 times that of the nylon 11 films (6.2 mC/m²). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient, d_h, of the bilaminate films also shows an enhancement with respect to the individual components, PVF₂ and nylon 11. ©1995 John Wiley & Sons, Inc.     

A Molecular Ferroelectric Showing Room‐Temperature Record‐Fast Switching of Spontaneous Polarization

Fast switching of spontaneous polarization (P_s) is one of the most essential requirements for ferroelectrics used in the field of data storage. However, in contrast to inorganic counterparts, the low operating frequency (<500 Hz) for molecular ferroelectrics severely hinders their large‐scale applications. Herein, for the first time, we achieved the room‐temperature fastest switching of the P_s in a new molecular ferroelectric, N‐methylmorpholinium trinitrophenolate ( 1 ), which displays notable ferroelectricity (P_s=3.2 μc cm^?2). Strikingly, electric polarizations of 1 have been switched under a record‐high frequency of 263 kHz, and this performance remains stable without any obvious fatigue after ca. 2×10⁵ switching cycles. To our knowledge, 1 is the first organic ferroelectric to switch polarization at such a high operating frequency, exceeding the majority of organic ferroelectrics, which opens up new possibilities for its potential in the field of non‐volatile memory.     

Influence of Plasticizers on the Electromechanical Behavior of a P(VDF‐TrFE‐CTFE) Terpolymer: Toward a High Performance of Electrostrictive Blends

This work aims at providing a complete analysis of the effect of plasticizers on the electrostrictive terpolymer performance. To achieve this, several plasticizing agents such as 2‐ethylhexyl phtalate (DEHP), diisononyl phtalate (DINP), and palamoll 652 have been incorporated in the polymer matrix. Experimental results demonstrate that the proposed novel materials exhibited excellent electromechanical enhancement in terms of transverse strain and mechanical energy density under a moderate electric field, which is definitively critical in recent microscale actuation. Another objective of this article was to explore material characteristics as a function of the DINP content, and it was found that the plasticizer weigh fraction was the key parameter determining performance of the modified fluorinate terpolymer blends. Accordingly, it was revealed that high performance flexible actuators can be achieved merely by employing a simple and cheap plasticizer, thus making it possible to overcome the current technological barrier of conventional electroactive polymers that suffer from the high applied electric field usually required to reach sufficient strain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 355–369     

Solvent‐Dependent Delamination,Restacking, and Ferroelectric Behavior in a New Charge‐Separated Layered Compound: [NH4][Ag3(C9H5NO4S)2(C13H14N2)2]⋅8 H2O

A new anionic coordination polymer, [NH₄][Ag₃(C₉H₅NO₄S)₂(C₁₃H₁₄N₂)₂] ⋅ 8 H₂O, with a two‐dimensional structure, has been synthesized by a reaction between silver nitrate, 8‐hydroxyquinoline‐5‐sulfonic acid (HQS), and 4,4′‐trimethylene dipyridine (TMDP). The compound stabilizes in a noncentrosymmetric space group, and the lattice water molecules and the charge‐compensating [NH₄]⁺ group occupy the inter‐lamellar spaces. The lattice water molecules can be fully removed and reinserted, which is accompanied by a crystalline–amorphous–crystalline transformation. This transformation resembles the collapse/delamination and restacking of the layers. To the best of our knowledge, this is the first observation of delamination and restacking in an inorganic coordination polymer that contains silver. The presence of a natural dipole (the anionic framework and cationic ammonium ions) along with the noncentrosymmetric space group gives rise to the room‐temperature ferroelectric behavior of the compound. The ferroelectric behavior is also water‐dependent and exhibits a ferroelectric–paraelectric transformation. The temperature‐dependent dielectric measurements indicate that the ferroelectric/ paraelectric transformation occurs at 320 K. This transformation has also been investigated by using in‐situ IR spectroscopy and PXRD studies. The second‐harmonic generation (SHG) study indicated values that are comparable to some of the known SHG solids, such as potassium dihydrogen phosphate (KDP) and urea.     

PbTiO3在压力下的异常相变和极强压电效应

运用第一性原理计算预言了在一纯化合物中可由压力诱导出顺序为叫方晶-单斜体-菱形体-立方体的新的相变，而且存在有变形相界面。在相变区有可与在复杂的单晶固溶体压电材料，如人们期待在机电应用方面引起革命性变化的Pb（Mg1/3Nb2/3）O3-PbTiO3可比的，极大的介电和压电耦合常数。我们的结果表明变形相界面和巨压电效应并不需要内禀的无序，并打开了在简单系统中研究这一效应的可能性，     

Frequency dependence of hysteresis associated with the electromechanical performance of PVDF film

The thickness strains, the electric displacements, and the hysteresis exhibited by poly(vinylidene fluoride) films under sinusoidal applied electric fields were measured over a range of frequencies from 0.05 to 100 Hz. The loops of strain‐ and electric displacement versus electric field exhibit a shape and hysteresis that undergoes a continuous and reversible change with frequency. At lower frequencies (<5 Hz), the shape and large hysteresis are characteristic of a ferroelectric with degrees of remanent polarization. At higher frequencies (>5 Hz), the shape and slight hysteresis of the loops are representative of a nonremanently polarized ferroelectric. This dependence of shape and hysteresis on frequency is attributed to the difference in rates between the rapid rate by which the polarization of domains of aligned dipoles is reversed in a periodic field and the slower rate by which the polarization is made remanent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3207–3214, 2007     

Physics of organic ferroelectric field‐effect transistors

Most of the envisaged applications of organic electronics require a nonvolatile memory that can be programmed, erased, and read electrically. Ferroelectric field‐effect transistors (FeFET) are especially suitable due to the nondestructive read‐out and low power consumption. Here, an analytical model is presented that describes the charge transport in organic FeFETs. The model combines an empirical expression for the ferroelectric polarization with a density dependent hopping charge transport in organic semiconductors. Transfer curves can be calculated with parameters that are directly linked to the physical properties of both the comprising ferroelectric and semiconductor materials. A unipolar FeFET switches between a polarized and depolarized state, and an ambipolar FeFET switches between two stable polarized states. A good agreement between experimental and calculated current is obtained. The method is generic; any other analytical model for the polarization and charge transport can be easily implemented and can be used to identify the origin of the different transconductances reported in the literature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Processing and characterization of oriented electrospun poly(vinylidene fluoride) mats

Mats of highly oriented poly(vinylidene fluoride) nanofibers were electrospun by means of a conventional electrospinning equipment; the orientation, however, was obtained using a disk collector rotating at a speed of 4000 rpm and a device that reduced the influence of air displacement during nanofiber orientation. Thermal transitions of the mats were determined by differential scanning calorimetry, the predominant crystalline phase by Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering and the nanofiber orientation and morphology by scanning electron microscopy. Relative permittivity, loss index, stable remnant polarization, and coercive field of the mats were also determined and compared with those obtained for a mat electrospun at 2000 rpm and an oriented commercial film. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2012     

Ho掺杂的BiFeO_3多铁陶瓷的制备及性能

用固相反应和快速退火冷却法制备了纯的BiFeO_3(BFO)陶瓷和15%Ho掺杂的Bi_(0.85)Ho_(0.15)FeO_3(BHFO)陶瓷,研究了室温下陶瓷的品格结构及其铁电、介电、漏电和磁性能.结果表明,Ho掺杂有助于减少BiFeO_3陶瓷中的杂相,改善其铁电、介电、漏电和磁性能.与BFO陶瓷相比,BHFO陶瓷具有典型的电滞回线;当电场强度为1 50 kV/cm时,其2Pr(剩余极化值)为15 μC/cm~2.同时,BHFO具有比BFO显著增大的介电常数和明显降低的介电损耗.磁性能测试表明,BHFO陶瓷表现出弱的铁磁性.     

Ferrimagnetism and abnormal spin lattice coupling in dilute magnetic ferroelectric (Bi0.46 Na0.46 Ba0.08)TiO3:Co

We have investigated the low-temperature magnetism and spin-lattice coupling in (Bi 0.46 Na 0.46 Ba 0.08)TiO 3:Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroelectrics.It is revealed that the as-prepared (Bi 0.46 Na 0.46 Ba 0.08)TiO 3:Co at Co content of 20%～30% exhibits fascinating ferrimagnetism which is robust against magnetic field,the abnormal spin-lattice coupling characterized by a negative magnetostriction effect;and the suppressed magnetic moment within the temperature range of 30 K～50 K is identified.These magnetic behaviours at low temperatures can be explained by the competition between the ferrimagnetic response and the magnetic moment suppression induced by the abnormal spin-lattice coupling effect.Finally,the ferroelectric and magnetodielectric properties are also discussed.