Ferroelectric Composites Research Articles

Pyroelectric performances of 1-3 ferroelectric composites based on barium titanate nanowires/polyvinylidene fluoride

Pyroelectric properties of 1–3 ceramic/polyvinylidene fluoride (PVDF) composites by using barium titanate nanowires (BTnws) and dopamine modified BTnws (DM-BTnws) as inclusions were firstly reported. 0–3 composites based on dopamine modified BT nanoparticles (DM-BTnps)/PVDF were also prepared for comparison. It was found that low contents of DM-BTnws in PVDF are beneficial for achieving high fraction of β-phase content based on the analysis results of X-ray diffraction (XRD), Fourier transform infrared (FTIR) and electric displacement-electric field (D-E) measurements. The enhancement of β-phase content in the DM-BTnws/composited film was believed to originate from strong hydrogen bonds interactions between poly-dopamine and PVDF molecules, which induced phase transition in PVDF from α-phase into β-phase. However, although DM-BTnws improved β-phase content and, accordingly, pyroelectric coefficient of the composites, they deteriorated dielectric performances of PVDF, reducing pyroelectric performances of the composites in terms of voltage and detectivity figures of merit.

Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3:ZnO relaxor ferroelectric composites with high breakdown electric field and large energy storage properties

0.82[0.94Bi0.5Na0.5TiO3-0.06BaTiO3]-0.18K0.5Na0.5NbO3:xZnO (BNT-BT-KNN:xZnO, x = 0-0.40) relaxor composites were prepared and their electrical properties were investigated. The breakdown electric field increases with increasing ZnO content. For x = 0 and x = 0.40 samples, the maximum recoverable energy storage density is 0.74 J/cm3 and 1.03 J/cm3 while the maximum energy storage efficiency is 86.7% and 72.7% under the electric field of 9.0 kV/mm and 14.0 kV/mm, respectively. The recoverable energy storage density and efficiency of the composite vary less than 2.5% from 25 °C to 125 °C, which indicates temperature-insensitive energy storage performance. These results are discussed based on the ZnO-enhanced bulk resistivity and the ZnO-induced local electric field which suppresses the evolution of polar nanoregions.

Enhanced electrocaloric effect in lead-free organic and inorganic relaxor ferroelectric composites near room temperature

We study the electrocaloric effect in the composites composed of the ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer matrix and lead-free BaZr0.2Ti0.8O3 (BZT) fillers. The P(VDF-TrFE-CFE)/BZT composite with 5 vol. % BZT exhibits a high adiabatic temperature change of ΔT = 7.4 K and a large isothermal entropy change of ΔS = 30 J kg−1 K−1 under an electric field of 90 MV m−1 at room temperature. The electrocaloric response in the composites is significantly enhanced when compared to those of the constituent components, which has been attributed to the polymer-filler interfacial coupling effect. In addition, the composites display a wide operational temperature window as a result of their ferroelectric relaxor nature.

Flexible Ferroelectric Sensors with Ultrahigh Pressure Sensitivity and Linear Response over Exceptionally Broad Pressure Range.

Flexible pressure sensors with a high sensitivity over a broad linear range can simplify wearable sensing systems without additional signal processing for the linear output, enabling device miniaturization and low power consumption. Here, we demonstrate a flexible ferroelectric sensor with ultrahigh pressure sensitivity and linear response over an exceptionally broad pressure range based on the material and structural design of ferroelectric composites with a multilayer interlocked microdome geometry. Due to the stress concentration between interlocked microdome arrays and increased contact area in the multilayer design, the flexible ferroelectric sensors could perceive static/dynamic pressure with high sensitivity (47.7 kPa-1, 1.3 Pa minimum detection). In addition, efficient stress distribution between stacked multilayers enables linear sensing over exceptionally broad pressure range (0.0013-353 kPa) with fast response time (20 ms) and high reliability over 5000 repetitive cycles even at an extremely high pressure of 272 kPa. Our sensor can be used to monitor diverse stimuli from a low to a high pressure range including weak gas flow, acoustic sound, wrist pulse pressure, respiration, and foot pressure with a single device.

Magneto-dielectric studies on multiferroic composites of Pr doped CoFe2O4 and Yb doped PbZrTiO3

Multiferroic composites with remarkable magnetoelectric effect (ME) are unique candidates for multifunctional devices. This study focuses on the structural, dielectric, ferroelectric, magnetic and ME properties of ferromagnetic (Pr doped CoFe2O4) and ferroelectric (Yb doped PbZrTiO3) composites with the general formula x CoPr0.1Fe1.9O4- (1-x) Pb0.95Yb0.05Zr0.52Ti0.48O3 (x = 0.02, 0.05 and 0.1). The individual phases namely Pr doped CoFe2O4 (CFO) and Yb doped PbZrTiO3 (PZT) for the composites were synthesized by sol-gel auto combustion technique. The powder X-ray diffraction technique showed that the Yb doped PZT retains its tetragonal perovskite structure, while as Pr doped CFO possesses cubic spinel structure. The morphological studies showed a uniform distribution of grains of parent phases in the composites. The dielectric studies in the temperature range of 100–750 K at a selected frequency (100 kHz) revealed a diffused phase transition confirming a ferroelectric to paraelectric phase transition. The composites show well-saturated P-E loops. The room temperature magnetic studies exhibit saturated M-H loops, with dilution of magnetic parameters for the composite. A favorable decrease in magneto-crystalline anisotropy calculated by Law of Approach was observed with decreasing ferrite content in the composite. The magneto-dielectric studies at room temperature confirm a negative magnetoelectric coupling in the composite. The Landau free energy approach confirmed a bi-quadratic coupling in the composites.

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites.

The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the depolarizing field of the bound charges of spontaneous polarization at the inclusions surface. The absence case shows that the Curie point shift is determined by the ratio of the Curie constant of the ferroelectric inclusion to the permittivity of the matrix. Screening effects show that the transition temperature shift decreases through multiplying the value by a decreasing factor equal to the ratio of the screening length to the radius of the ferroelectric inclusion. Examples of the materials for the position of the Curie point on the temperature scale, largely determined by the tilting action of the depolarizing field and the compensating shielding effects, are given.

On the Electret Effect in Polymer–Ferroelectric Piezoceramic Composites with Various Values of the Electronegativity of the Polymer Matrix and Piezophase Cations

The influence of the electronegativity of phases, which is controlled by composite crystallization under the conditions of the effect of the electric discharge and covalence of piezophase cations, on the formation mechanism of the stable electret effect is determined. The specific features of the formation of the electret effect in composites based on polyolefins (HDPE, PP), fluorine-containing polymers (F42), and ferroelectric piezoelectric ceramics of the family of lead zirconate–titanate (Pb(Zr,Ti)O3) crystallized under conditions of the effect of electric discharge plasma, are revealed. A physical model of electret composites taking into account the role of homocharges and heterocharges formed in a composite by its dispersion with piezoceramic particles of various structures—rhombohedral, tetragonal, and heterogeneous—is proposed.

Компьютерное молекулярное моделирование пьезоэлектрических свойств сегнетоэлектрических композитов на основе поливинилиден-фторида с графеном и оксидом графена

Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF), graphene (G) and/or graphene oxide (GO), was performed using the semi-empirical quantum approximation PM3 in the HyperChem software package. The piezoelectric properties of the composites were analyzed and compared with the experimental data obtained for thin films containing poly(vinylidene-fluoride-trifluoroethylene) with graphene oxide (P (VDF-TrFE)/GO). A qualitative agreement was obtained between the simulation results and the experimental measurements of the piezoelectric coefficient, its decrease in the presence of G or GO was revealed. When models containing one or more layers of graphene with 54 carbon atoms were investigated, it was found that the average piezoelectric coefficient was reduced to -9.8 pm/V for the one-sided PVDF/G model and to -18.98 pm/V for the two-sided sandwich model G/PVDF/G in compare with the calculated piezoelectric coefficient for pure PVDF (-42.2 pm/V). After computer modeling for models incorporating one or more layers of 96 carbon atoms in the oxide graphene, it was found that the piezoelectric coefficient was reduced to a value of -14.6 pm/V for a one-sided PVDF / GO model and to a value of -29.8 pm/V for a two-sided sandwich model GO/ PVDF/GO compared to the piezoelectric coefficient for pure PVDF.

Dielectric properties of (1−x)KNbO3−xNiO two-phase composites

We report a detailed study on structural and dielectric properties, Raman scattering, and ac-conductivity of ferroelectric KNbO3 and antiferromagnetic NiO two-phase composites [() KNbO3 + x NiO]. Two major transitions were observed in the temperature dependent relative dielectric permittivity (T)—the first at C () and the second at C (T1)—respectively associated with the structural transitions from tetragonal to cubic and orthorhombic to tetragonal phases. In addition, a new anomaly across T2 ∼ C has been observed in (T), and the loss-tangent (Tanδ(T)), which may be associated with the combined effect of antiferromagnetic ordering of NiO and ferroelectric coupling of KNbO3. The dispersive nature of , and the Vogel–Fulcher temperature dependence of its characteristic relaxation frequency reveals the existence of relaxor-like behavior, which is further supported by Uchino–Nomura criteria (for x ⩽ ) but departs from relaxor behavior for x . Temperature dependent ac-resistivity analysis (T) provides strong evidence for a Mott’s Variable range hopping process of charge carriers between localized states, with average hopping length of nm and hopping energy eV. The variation of , T1 and T2 as a function of x, in consonance with the crystal structure, has been discussed. Raman spectroscopic studies were carried out to study the local structure of the () + x NiO two-phase composites, which shows significant increase of tilt-angle between adjacent octahedra as the divalent Ni occupies octahedral sites of the matrix. All the Raman-active modes of these composites are indexed as lattice translations, specifically with the motion of (190 ), the core vibrations of the octahedra (220 ⩽ ν ⩽ 320 ) and their collective modes (50 ⩽ ν ⩽ 150 ), and Magnon modes (2M ∼ 1500 ) associated with the antiferromagnetic ordering of NiO.

Stabilization of the NOP ferroelectric phase in potassium nitrate–barium titanate ferroelectric composites

The study of temperature evolution of KNO3 (NOP) structure in ferroelectric (1−x)KNO3 + (x)BaTiO3 composites with BaTiO3 concentrations х = 0.25, 0.50 and 0.53 has been carried out on cooling with the use of the neutron diffraction technique. It was shown that, on cooling, the phase transition temperature (Tc) from the high-temperature paraelectric phase into the ferroelectric one did not depend on barium titanate concentration and practically coincided with Tc for pure NOP. Moreover, it was found that the admixture of BaTiO3 essentially enlarged the temperature range of NOP ferroelectric phase stability in the composites with BaTiO3 concentrations x = 0.25 and 0.50. The suppression of the ferroelectric phase was observed for the composite with x = 0.53.

Multiferroic properties of ferromagnetic and ferroelectric coupled Mn-Zn ferrite-BaTiO3 composite

ABSTRACTThe magneto-dielectric properties can be tuned through ferromagnetic–ferroelectric composites with different Mn0.9Zn0.1FeO4 to BaTiO3 ratio. The two phenomena can couple and interact with each other when they exist simultaneously due to induced electric polarization in the magnetic order. The composites were synthesized using the nanoparticles of Mn0.9Zn0.1Fe2O4 and BaTiO3 with different composition by sintering at 1000°C. The X-ray diffraction confirms the coexistence of ferromagnetic and ferroelectric phases. The surface micrographs show variations in the porosity along with two types of inter grain connectivity. The magnetic and ferroelectric hysteresis loops confirm the magneto-electric coupling presents in the composites.

Stress-induced phase transition in lead-free relaxor ferroelectric composites

Piezoelectric materials are considered an enabling technology generating an annual turnover of about 20 billion $. At present, lead-based materials dominate the market with the known risk to health and environment. One of the three key competitors for their replacement is the class of sodium bismuth titanate (NBT)-based relaxor ferroelectrics, the use of which is limited by thermal depolarization. An increased thermal stability has recently been experimentally demonstrated for composites of Na1/2Bi1/2TiO3-6BaTiO3 with ZnO inclusions (NBT-6BT:xZnO). However, the exact mechanism for this enhancement still remains to be clarified. In this study, piezoresponse force microscopy and 23Na NMR spectroscopy were used to demonstrate that the incorporation of ZnO leads to a stabilization of the induced ferroelectric state at room temperature. Temperature-dependent measurements of the relative dielectric permittivity ε′(T), the piezoelectric coefficient d33 and the strain response revealed an increase of the working temperature by 37 °C. A simple mechanics model suggests that thermal deviatoric stresses stabilize the ferroelectric phase and increase, as well as broaden, the temperature range of depolarization. Our results reveal a generally applicable mechanism of enhancing phase stability in relaxor ferroelectric materials, which is also valid for phase diagrams of other ceramic matrix composites.

Crystallization kinetics and enhanced dielectric properties of free standing lead-free PVDF based composite films

Ferroelectric composites, integrating dielectric ceramic fillers with mechanically flexible polymers, are promising materials for flexible electronic applications. Plenty of research has demonstrated the enhanced dielectric and ferroelectric properties of composite materials. However, the mechanisms responsible for these enhancements are not completely understood. Herein, we used typical dielectric materials, poly(vinylidene fluoride) (PVDF) and BaTiO3 (BTO), to study the effect of a dielectric filler on the crystallization, phase transformation and dielectric properties of PVDF. The crystallization of β-PVDF was not affected by the presence of BTO particles, but small amounts of BTO (< 3 vol %) made PVDF crystallize into larger spherulites. This is linked to crystallization kinetic studies, which showed that BTO acted as a nucleation agent for large full ring banded spherulites when its content was less than 1 vol %. Furthermore, solid state drawing in the presence of BTO particles promoted the formation of β-PVDF with more pronounced preferred crystalline orientation at high drawing temperatures (120 °C). The dielectric and ferroelectric properties were enhanced with BTO filling. The 100 °C oriented drawn PVDF tape exhibited a dielectric permittivity of 14 (100 Hz) and remnant polarization of 0.080 C/m2 (10 Hz), which increased to 23 and 0.095 C/m2, respectively, after filling with 5 vol % BTO; neither resulting in high dielectric loss tangent (∼ 0.02) nor obvious current leakage. Moreover, the coercive field decreased from 80 to 50 kV/mm with increasing BTO content from 0 to 5 vol %.

Dielectric properties of the polymer–matrix composites based on the system of Co-modified potassium titanate–polytetrafluorethylene

Powdered ceramic composites based on the amorphous potassium polytitanate modified in aqueous solutions of cobalt sulfate and calcined at 700℃ (PPT-Co) were used as the ceramic filler of the polytetrafluorethylene–matrix composite dielectrics characterized with high permittivity and low dielectric losses. The influence of the ceramic filler content on the electrical properties of the produced composites was investigated in the range of 1–50 wt%. The obtained results were compared with the data reported in literature for other ferroelectric composites based on polytetrafluorethylene and were analyzed taking into account some theoretical models earlier proposed for the two-component systems. An influence of the temperature on the frequency dependence of permittivity at 30–150℃ for the composites with different filler contents was investigated.

Molecular modeling of the piezoelectric properties of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene or graphene oxide.

Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene (G) or graphene oxide (GO) were performed using the semi-empirical quantum approximation PM3 in HyperChem. The piezo properties of the composites were analyzed and compared with experimental data obtained for P(VDF-TrFE)-GO films. Qualitative agreement was obtained between the results of the modeling and the experimental results in terms of the properties of the measured effective piezoelectric coefficient d 33eff and its decrease in the presence of G/GO in comparison with the average computed piezoelectric coefficient <d 33>. When models incorporating one or several G layers with 54 carbon atoms were investigated, the average piezoelectric coefficient <d 33> was found to decrease to -9.8pm/V for the one-sided model PVDF/G and to -18.98pm/V for the sandwich model G/PVDF/G as compared with the calculated piezoelectric coefficient for pure PVDF (<d 33> = -42.2pm/V computed in present work, and <d33> = -38.5 pm/V, obtained from J Mol Model 35 (2013) 19:3591-3602). When models incorporating one or several GO layers with 98 carbon atoms were considered, the piezoelectric coefficient was found to decrease to -14.6pm/V for the one-sided PVDF/GO model and to -29.8pm/V for the sandwich GO/PVDF/GO model as compared with the samecalculated piezoelectric coefficient for pure PVDF.

Graphene/graphene oxide and polyvinylidene fluoride polymer ferroelectric composites for multifunctional applications

ABSTRACTWe perform computational molecular modeling of graphene/graphene oxide (G/GO) and polyvinylidene fluoride (PVDF) ferroelectric polymer composite nanostructures, using semi-empirical quantum approximation PM3 in HyperChem. Piezoelectric properties of these nanostructures are analyzed in comparison with experimental data obtained for poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE)-GO thin films. Modeling shows qualitative agreement of properties and lowering of piezoelectric coefficient d33eff values under influence of G/GO layers. Modeling of GO-methane-hydrates nanostructures based on hexagonal ice model shows that after relaxation the system keeps a stable deformed state. This can serve for gas-hydrates storage and separation. Modeled composites could be used as multifunctional molecular units.

Polyvinylidene fluoride/hydroxyapatite/β-tricalcium phosphate multifunctional biocomposite: Potentialities for bone tissue engineering

Bioactive ferroelectric composites based on polyvinylidene fluoride, hydroxyapatite and β-tricalcium phosphate have been synthesized and their structural, microstructural, bioactive, and ferroelectric properties are characterized. Structural and FTIR investigations showed the presence of the polar polyvinylidene fluoride (β2) phase, while ferroelectric characterizations revealed remnant polarizations and coercive field, around 0.04 μC/cm2 and 28 kV/cm, respectively, for these biocompatible samples. Structural and microstructural analysis of samples previously immersed in simulated body fluid for 7 days revealed a large apatite phase growth (1.45 μm) on the composites' surfaces as a strong indication of their elevated bioactivity and potentialities for bone tissue engineering.

Computational study of textured ferroelectric polycrystals: Dielectric and piezoelectric properties of template-matrix composites

Quantitative relationships between processing, microstructure, and properties in textured ferroelectric polycrystals and the underlying responsible mechanisms are investigated by phase field modeling and computer simulation. This study focuses on three important aspects of textured ferroelectric ceramics: (i) grain microstructure evolution during templated grain growth processing, (ii) crystallographic texture development as a function of volume fraction and seed size of the templates, and (iii) dielectric and piezoelectric properties of the obtained template-matrix composites of textured polycrystals. Findings on the third aspect are presented here, while an accompanying paper of this work reports findings on the first two aspects. In this paper, the competing effects of crystallographic texture and template seed volume fraction on the dielectric and piezoelectric properties of ferroelectric polycrystals are investigated. The phase field model of ferroelectric composites consisting of template seeds embedded in matrix grains is developed to simulate domain evolution, polarization-electric field (P-E), and strain-electric field (ε-E) hysteresis loops. The coercive field, remnant polarization, dielectric permittivity, piezoelectric coefficient, and dissipation factor are studied as a function of grain texture and template seed volume fraction. It is found that, while crystallographic texture significantly improves the polycrystal properties towards those of single crystals, a higher volume fraction of template seeds tends to decrease the electromechanical properties, thus canceling the advantage of ferroelectric polycrystals textured by templated grain growth processing. This competing detrimental effect is shown to arise from the composite effect, where the template phase possesses material properties inferior to the matrix phase, causing mechanical clamping and charge accumulation at inter-phase interfaces between matrix and template inclusions. The computational results are compared with complementary experiments, where good agreement is obtained.

Functionally graded ferroelectric polyetherimide composites for high temperature sensing

High temperature flexible ferroelectrics for thermally stable devices that can detect pressure are fabricated by careful design of the microstructure.

Time-resolved fluorescence and absence of Förster resonance energy transfer in ferroelectric liquid crystal-quantum dots composites

The present article deals with the interaction of octadecylamine (ODA) capped cadmium selenide quantum dots (CdSe QDs) and two ferroelectric liquid crystals (FLCs) having different values of spontaneous polarization (Ps). The pristine FLCs and FLC-QDs composites have been investigated by using steady-state and time-resolved fluorescence spectroscopic techniques. Stokes shift and the preferred alignment of FLC molecules in the presence of QDs are found to depend on the secondary order parameter of FLCs (i.e. Ps). The secondary fluorescence emissions have been strongly influenced by the concentration of QDs. The Förster resonance energy Transfer (FRET) was absent in both the composites. This article discloses the role of various factors, like relative orientation, dipolar interaction between donor and acceptor and the proximity of QDs (>10 nm), which might be responsible for the absence of FRET. FLC-QDs composites do not form a new class of luminescent material though the fluorescence properties of host FLCs are tailored in the presence of QDs by means of the change in molecular alignment. The change in lifetimes of FLC-QDs composites has not been observed.