Correlating the Interfacial Polar-Phase Structure to the Local Chemistry in Ferroelectric Polymer Nanocomposites by Combined Scanning Probe Microscopy

Ferroelectric polymer nanocomposites possess exceptional electric properties with respect to the two otherwise uniform phases,which is commonly attributed to the critical role of the matrix-particle interfacial region.However,the structure-property correlation of the interface remains unestablished,and thus,the design of ferroelectric polymer nanocompos-ite has largely relied on the trial-and-error method.Here,a strategy that combines multi-mode scanning probe microscopy-based electrical charac-terization and nano-infrared spectroscopy is developed to unveil the local structure-property correlation of the interface in ferroelectric polymer nano-composites.The results show that the type of surface modifiers decorated on the nanoparticles can significantly influence the local polar-phase content and the piezoelectric effect of the polymer matrix surrounding the nano-particles.The strongly coupled polar-phase content and piezoelectric effect measured directly in the interfacial region as well as the computed bonding energy suggest that the property enhancement originates from the formation of hydrogen bond between the surface modifiers and the ferroelectric polymer.It is also directly detected that the local domain size of the ferroelectric polymer can impact the energy level and distribution of charge traps in the interfacial region and eventually influence the local dielectric strength.

Three dimensional phase field study on the thickness effect of ferroelectric polymer thin film

The electromechanical behavior of poly(vinylidene fluoride-trifluoroethylene)[P(VDF -TrFE)]ferroelectric thin film was investigated using the three dimensional(3D) phase-field method. Various energetic contributions,including elastic,electrostatic,and domain wall energy were taken into account in the variational functional of the phase field model.Evolution of the microscopic domain structures of P(VDF-TrFE) polymer film was simulated.Effects of the in-plane residual stress,the film thickness and externally applied electric bias field on the electromechanical properties of the film were explored.The obtained numerical results showed that the macroscopic responses of the electric hysteresis loops are sensitive to the residual stress and electric bias field.It was also found that thickness has a great effect on the electric hysteresis loops and remanent polarization.

EFFECT OF CRYSTALLINITY ON POLARIZATION FATIGUE OF FERROELECTRIC P(VDF-TrFE)COPOLYMER FILMS

The dependence of polarization fatigue on crystallinity of vinylidene fluoride and trifluoroethylene copolymer films was studied.Experimental data indicated that the higher the crystallinity of the film was,the slower the fatigue rate of the film became.A possible explanation was put forward,and it was regarded that the space charges,trapped at the boundaries of crystallites and/or captured by the defects lying both in amorphous and crystalline phases,should make the major contribution to polarization fatig...

Field-effect transistor memories based on ferroelectric polymers

Field-effect transistors based on ferroelectrics have attracted intensive interests, because of their non-volatile data retention, rewritability, and non-destructive read-out. In particular, polymeric materials that possess ferroelectric properties are promising for the fabrications of memory devices with high performance, low cost, and large-area manufacturing, by virtue of their good solubility, low-temperature processability, and good chemical stability. In this review, we discuss the material characteristics of ferroelectric polymers, providing an update on the current development of ferroelectric field-effect transistors（Fe-FETs） in non-volatile memory applications.

Polarization fatigue in poly(vinylidene fluoride (78%)-trifluoroethylene (22%)) ferroelectric thin films:a pulse train study

This paper investigates the influences of polarization fatigue on remanent polarization and switching time by pulse train measurements in ferroelectric poly（vinylidene fluoride （78%） and trifluoroethylene （22%）） thin films. Fatigue was carried out by a series of bipolar switching pulses with constant pulse width （on-time） and various interval times between pulses （off-time）. The experimental observations indicated that the off-time period showed no obvious influence on fatigue rate and the switching time increased with the increase of fatigue cycles. The origination of these phenomena was discussed according to the charge injection model.

Molecular Modulation of Structure and Ferroelectric Performance of Poly(vinylidene fluoride)Free Standing Films from Aspects of Molecular Weight and Crystallization Temperature

Ferroelectric polymer poly(vinylidene fluoride)(PVDF)has received great research interest because of its special electroactive properties which are strongly dependent on the crystalline structures and in turn processing conditions.The effect of molecular weight and crystallization temperature on the micro-structure and macro-properties of PVDF films casted from dimethyl sulfoxide(DMSO)solvent is investigated.The results demonstrated that a low molecular weight(180 kg/mol)and a low evaporation temperature(50℃)favored the formation of polarγ-phase,while a high molecular weight(1000 kg/mol)and a high evaporation temperature(125℃)made PVDF crystallize intoα-phase.Compared with films casted at 50℃,films casted at 125℃exhibited higher dielectric loss at a low electric field and less loss conductivity at a high electric field,which was due to their low degrees of crystallinity and fine evaporation of the solvent,respectively.PVDF with a molecular weight of 180 kg/mol casted at 125℃exhibited the highest remnant polarization(0.062 C/m^(2))among all of the solution-processed films,being a result of high chain mobility resulted from the low molecular weight.

Dielectric properties of composite based on ferroelectric copolymer of poly(vinylidene fluoride-trifluoroethylene)and ferroelectric ceramics of barium lead zirconate titanate

A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene)copolymer P(VDFTrFE)and ferroelectric ceramics of barium lead zirconate titanate(BPZT)solid solution is presented in this work.The composite films containing up to 50 vol.%of BPZT grains with size
1
m were prepared by the solvent cast method.Frequency dependences of real and imaginary components of the complex permittivity were determined.The concentration dependence of the dielectric constant was discussed.

Dielectric phenomena and electrical energy storage of poly(vinylidene fluoride) based high-k polymers

Polymeric dielectrics have wide range of applications in the field of electrical energy storage because of their light weight and easy processing. However, the state-of-the-art polymer dielectrics, such as biaxially orientated polypropylene, could not meet the demand of minimization of electronic devices because of its low energy density. Recently, poly（vinylidene fluoride） （PVDF） based ferroelectric polymers have attracted considerable interests for energy storage applications because of their high permittivity and high breakdown strength. Unfortunately, the high dielectric loss and/or high remnant polarization of PVDF-based polymers seriously limits their practical applications for electrical energy storage. Since the discovery of relaxor ferroelectric behavior was firstly reported in irradiated poly（vinylidene fluoride- trifluoroethylene） （P（VDF-TrFE）） copolyrner, many strategies have been developed to enhanced the electrical energy storage capability, including copolymerization, grafting, blending and fabricating of multilayer How these methods affect the polymorphs, crystallinity, crystal size of PVDF-based polymers and the connection between these microstructures and their corresponding energy storage properties are discussed in detail.

LARGE ELECTROCALORIC EFFECT IN RELAXOR FERROELECTRICS

Organic and inorganic relaxor ferroelectrics used for electrocaloric effect(ECE)applications areintroduced.Relaxor ferroelectrics offer several advantages for ECE devices,e.g.,infinite stateswithout applying electric field,field-induced large polarization,no-hysteresis ofheating and cooling,small-hysteresis polarization loss,room temperature phase transition,and broad temperaturerange.The ECE in relaxor ferroelectrics under a high electric field can be described using a theorysimilar to that for first-order phase transition materials.Large ECE was observed directly inhigh-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)68/32 mol%copolymers,P(VDF-TrFE-CFE)(CFE-chlorofluoroethylene)59.2/33.6/7.2 mol%terpolymers,P(vDF-TrFE-CFE)-P(VDF-CTFE)(CTFE-chlorotrifluoroethylene)95/5 wt%terpolymer blended films,and(PbLa)(ZrTi)O_(3)(PLZT)ceramic thin films.ECE reported inPb(Sc_(1/2)Ta_(1/2))O_(3)(PST),Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)(PMN-PT)thin films is also summarized.Finally,the perspective of ECE devices is llustrated.

Direct measurement of electrocaloric effect in P(VDF-TrFE-CFE)film using infrared imaging

Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)P(VDF-TrFE-CFE)is a relaxor ferroelectric polymer,which exhibits a temperature-independent electrocaloric effect at room temperature.In this work,the electrocaloric effect in P(VDF-TrFE-CFE)film was directly analysed using infrared imaging.P(VDF-TrFE-CFE)64.8%/27.4%/7.8%(in mole)film of(15±1)mm thickness was deposited on polyethylene naphthalate substrate.Direct ECE of P(VDF-TrFE-CFE)film was measured from 15 to 35
C at different electric fields.A maximum adiabatic temperature change(DTad)of 3.58 K was measured during the cooling cycle at a field of 100 V/mm at 30
C.Finite element analysis of temperature dissipation through the sample estimated that the actual temperature change within P(VDF-TrFE-CFE)film was 4.3 K.Despite the thermal mass of the substrate,a substantial ECE was observed in P(VDF-TrFE-CFE)films.This electrocaloric terpolymer composition could be of interest for electrocaloric cooling applications.

Electrical characterization of poly(vinylidene fluoride-trifluoroethylene) nanocrystals embedded in porous alumina matrix

In this work,the study of dielectric properties of composite structures on the base of poly(vinylidene fluoride-triflouroethylene)copolymer P(VDF-TrFE)and porous aluminum oxide layers produced by the melt-impregnation is presented.Frequency dependences of dielectric characteristics of the composite samples were determined.The dielectric dispersion and ferroelectric switching processes in the composite structures were discussed.