P(VDF/TrFE), a versatile ferroelectric polymer, holds immense promise for diverse applications, but optimizing its ferroelectric properties has been a major bottleneck. We present a groundbreaking approach, demonstrating a remarkable 48 % enhancement in polarization through a precise control of the cooling rate after annealing. Slow cooling at 0.5 degrees C/min significantly enhances the f-phase crystallinity, the ferroelectrically active phase, as evidenced by X-ray diffraction. This improved crystallinity directly contributes to the observed polarization enhancement. Dielectric analysis reveals a strong link between cooling rate and molecular alignment, with slower cooling leading to a higher dielectric constant, indicative of superior chain order. This improved order facilitates more efficient polarization switching, further contributing to the enhanced ferroelectricity. Our study unveils the often-overlooked impact of cooling rate on the ferroelectric properties of P(VDF/TrFE) thin films. By manipulating the cooling speed after annealing, we can effectively tailor the material's ferroelectricity, opening new avenues for optimizing device performance and expanding its application potential.

A hybrid piezo/triboelectric nanogenerator (H/P-TENG) is designed for mechanical energy harvesting using polymer ceramic composite films; polydimethylsiloxane/Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (PDMS/BZT-BCT) and polyvinyl alcohol (PVA). A lead-free BZT-BCT piezoelectric ceramic was prepared via solid-state method and blended into PDMS to form a series of polymer-ceramic composite films, ranging from 5% to 30% by weight. The films were forward/reverse poled with corona poling and their electrical properties were compared to non-poled samples. The H/P-TENG constructed with forward-poled 15 wt% BZT-BCT in PDMS achieved the highest open-circuit voltage, V oc of 127 V, short-circuit current density, J sc of 67 mA m-2, short-circuit charge density, Q sc of 118 μC m-2, and peak power density of 7.5 W m-2, an increase of 190% over pristine PDMS-based TENG. It was discovered that incorporating BZT-BCT into the PDMS matrix improved the triboelectric properties of PDMS. The overlapping electron cloud (OEC) model was used to explain the enhancement and the effect of poling direction of the PDMS/BZT-BCT composite used in H/P-TENG, providing fundamental knowledge of the influence of piezoelectric polarisation on contact electrification.

Piezoelectric resonance spectroscopy was employed to elucidate the microscopic mechanisms of piezoelectricity and its relaxation for the uniaxially-drawn and poled films of polyvinylidene fluoride and the vinylidene fluo-ride/ trifluoroethylene copolymer with a composition of 75/25 mol. The former was semicrystalline whereas the latter consisted of extended-chain crystals. Accurate measurements of dielectric frequency spectra in the mHz-toGHz range revealed piezoelectric resonance superimposed on broad dielectric relaxation. Analyses of the resonance spectra of the length, width and thickness vibrations allowed for evaluation of all elastic and piezoelectric tensor components. The single-crystalline copolymer substantiated the crystalline relaxation associated with intramolecular rotational fluctuations of trans segments and longitudinal chain softening. The most informative were the piezoelectric e(31), e(32), and e(33) constants expressing the charge responses induced by chain elongation, interchain separations parallel and perpendicular to thickness, respectively. It was found that e(31) showed relaxation from small negative to large positive, and e(33) was much larger than e(32) both being negative and non-relaxational. These results were discussed in reference to those of Form I crystals whose polar axis was p/6 tilted due to (110) twin. We identified three microscopic mechanisms (i) elongation of relaxing chain reduces the effective monomer dipole moment mu due to reduction of rotational fluctuations, (e(31) > 0), (ii) the increase in interchain distance reduces mu due to decrease in positive local field, (e(32), e(33) < 0), (iii) the strain-induced reduction of dipole density (dimensional effect) is effective in experimental e(33) but is absent in e(32) and e(31). The piezoelectric tensor components determined in this study were consistent with the electrostrictive coupling measured from the strain-induced change in dielectric permittivity and the strain proportional to the square of polarization.

Piezoelectric resonance spectroscopy was used to evaluate the face shear piezoelectricity and its relaxation for structurally controlled poly-L-lactic acid (PLLA) films. We prepared samples by uniaxial drawing at 80 degrees C for a ratio of 2-6 and annealed at temperatures above glass transition (Tg = 60 degrees C) to below melting (Tm = 170 degrees C) for 1 hour. The degrees of crystallinity Xc and orientation Fc by X-ray diffraction were controlled over a broad range to reach Xc = 0.8 and Fc = 0.9. We measured broadband dielectric spectra where the piezoelectric resonance was observed superimposed on dielectric relaxation. Analyses of the resonance spectra for 45 degrees -cut square sample resulted in the determination of the face-shear piezoelectric constants e14 and d14, as well as the elastic shear compliance s44 and stiffness c44. At room temperature, e14 was shown to be proportional to a product of Xc*Fc, whereas d14 demonstrated saturation due to an increase in c44. By extrapolating to Xc*Fc =1, the e14 of PLLA crystal was determined. As the temperature increases, piezoelectric relaxation due to non-crystalline segmental motion was observed as well as dielectric and elastic relaxation. It was found that e14 decreased in a similar manner to c44 whereas d14 increased slightly with increasing temperature. The temperature dispersions of e14, d14 and c44 were reproduced using an equivalent three-spring model consisting of a crystalline piezoelectric spring connected by series and parallel non-crystalline relaxational springs based on the temperaturefrequency reduction rule and the VTF-type dielectric relaxation time. The findings revealed key information on the ratio of noncrystalline phases connected in series and parallel to the oriented crystalline phase.

The effects of solvents and temperature on the crystal formation were investigated for vinylidene fluoride/trifluoroethylene copolymer P(VDF-TrFE). Highly crystalline P(VDF-TrFE) thin films were fabricated by spin-casting using various polar solvents such as diethyl carbonate (DEC), methyl ethyl ketone (MEK), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Ferroelectric polarisation reversal of the P(VDF-TrFE) was evidenced by a displacement (D)-electric field (E) hysteresis loop measurement and supported by the presence of pyroelectric activity. The samples which were annealed above 100 °C gave elongated rod-like crystalline structures and the highest crystallinity, Xc of 83% was formed at 120 °C. Consequently, remnant polarisation (85 mC m-2) and the pyroelectric coefficient (30 μC m-2 K-1) were enhanced. Thus, annealing plays a substantial role in controlling the crystalline structure of P(VDF-TrFE) films regardless of the choice of solvent. Although, the crystalline structure control is almost independent of the solvent's polarity, the choice of solvent is essential in preparing a smoother film surface. Molecular dynamics of P(VDF-TrFE) are discussed from the observation of two dielectric relaxation processes, β and γ related to the segmental micro-Brownian and local modes, respectively. The complete ferroelectric polarization reversal caused a reduction in the dielectric polarization and reduced the lattice spacing of the 110/200 planes.

The ferroelectric, pyroelectric, and dielectric properties of 0-3 nanocomposite systems of ferroelectric (Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3 ceramics with a vinylidene fluoride/trifluoethylene copolymer were investigated. It was observed that the interface effect between the polymer matrix and nanofiller improves the polarization response in nanocomposite. As a result, significant enhancements in remnant polarization of 130 mC/m(2) and pyroelectric sensitivity of 90 mu C/m(2)K are achieved compared to 85 mu C/m(2) and 26 mu C/m(2)K for pure polymer matrix. Full ferroelectric polarization reversal in the nanocomposite system was supported by a displacement (D) - electric field (E) hysteresis loop and evidence of pyroelectric activity. This finding suggests that the local field plays an important key in facilitating the poling procedure. Therefore, the functional electrical properties of the nanocomposites can be significantly enhanced by controlling the permittivity and conductivity of the inorganic ferroelectric ceramic nanofiller to match the required parameters. Microscopic features of the ferroelectric polarization are also discussed in terms of a two-step switching process. The approach developed her open the way of rational design and assembly of lead free nanocomposite as flexible, light and high performance smart materials, satisfying various requirements for emerging applications. (c) 2018 Elsevier Ltd. All rights reserved.

The crystallinity and miscibility behavior of poly (vinylidene fluoride)/poly (L-lactic) acid (PVDF/PLLA) blend over a wide composition range in solution and cast film were investigated. The blend films were characterized using Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD) and Viscometry measurement. The interaction parameters were calculated using Pinping, Krigbaum and Garcia's interpretation which were derived from Flory-Huggins theory. The calculation revealed that the PVDF/PLLA blend is miscible for all composition in the solution. DSC results shows two shifted glass transition temperature indicating blends are partially miscible in the solid state. The partial miscibility was due to the molecular interaction between –C=O of PLLA and -C-H of PVDF evidenced from the FTIR spectrum. Moreover, PLLA in the blend could enhance the overall crystallinity of the samples.

Spin coated polyvinlylidenefluoride-trifluoroetylene (PVDF-TrFE 70/30mol%) copolymer thin film were initially produced and annealed at varying temperatures (100 degrees C to 160 degrees C). The morphology, dielectric and ferroelectric analysis showed that PVDF-TrFE film annealed at 120 degrees C produced the highest remnant polarization, P-r of 92 mC/m(2), with orderly and grain-like shaped crystallites. The filled PVDF-TrFE, loaded with various volume percentages (1 - 7%) of Magnesium Oxide (MgO) nanofillers and then, annealed at 120 degrees C, produced homogenous filler distribution with low agglomerates, especially for 3% PVDF-TrFE filled films. Moreover, the annealed PVDF-TrFE/MgO(3%) generated the highest value of Pr in comparison to the other filled nanocomposite thin films. Most importantly, the saturation of hysteresis loop, P-s for annealed PVDF-TrFE/MgO(3%) film was relatively improved by 20% as compared to the unfilled annealed thin film. This study established that, 3% MgO loaded in PVDF-TrFE thin film and annealed at 120 degrees C demonstrated a stable ferroelectric thin film, closed to an ideal ferroelectric film, in which the ratio P-r/P-s for the film established a value approaching unity (value of 1).

The capacitor device has evolved from a simple device to an innovative and complex device. The capability of a capacitor is very much dependent on capacitance performance. Currently, researchers have shown interest in hybrid composites, which are capable of improving performance and increase reliability of devices. Thus, there is a need to fabricate thin films of hybrid dielectric materials such as polymer (PVDF-TrFE) and ceramic (PbTiO3). This study presents the preparation of the PVDF-TrFE layer for bilayer composite PbTiO3/PVDF-TrFE configured as metal-insulator-metal films capacitor. The deposition process utilised two methods: solvent casting and spin coating. The ceramic layer (first layer), PbTiO3, has optimum dielectric permittivity and tangent loss of about 138 and 0.9 taken at 1 kHz. The polymeric spin-coated layer (second layer) PVDF-TrFE films produced good dielectric property as compared to solvent casting prepared films. This provides an opportunity for further investigation of the dielectric property for enhanced understanding of capacitor-based devices.

The molecular dynamics of a synthetic branched chain glycolipid, 2-decyl-tetradecyl-β-d-maltoside (C14-10G2), in the dry assemblage of smectic and columnar liquid crystal phases has been studied by dielectric spectroscopy as a function of frequency and temperature during the cooling process. Strong relaxation modes were observed corresponding to the tilted smectic and columnar phases, respectively. At low frequency (∼900 Hz to 1 kHz) in the smectic phase, Process I* was observed due to the tilted sugar bilayer structure. The process continued in the columnar phase (Process I) with an abrupt dynamic change due to phase transition in the frequency range of ∼1.3 kHz to 22 kHz. An additional process (Process II) was observed in the columnar phase with a broader relaxation in the frequency range of ∼10 Hz to 1 kHz. A bias field dependence study was performed in the columnar phase and we found that the relaxation strength rapidly decreased with increased applied dc bias field. This relaxation originates from a collective motion of polar groups within the columns. The results of dielectric spectroscopy were supported by a molecular dynamics simulation study to identify the origin of the relaxation processes, which could be related to the chirality and hydrogen bonds of the sugar lipid.

Sr0.5Ba0.5Nb2O6 (SBN50) ceramic doped with different concentrations of Cerium (Ce) according to the stoichiometry formulation of Sr0.5-3y/2Ba0.5CeyNb2O6 (Ce-SBN) with y = 0, 0.01, 0.02, 0.03, 0.04 and 0.05 was prepared using the conventional solid state reaction method. The morphology, structure, and electrical properties of the samples were studied using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), ferroelectric and dielectric spectroscopy, respectively. The FESEM images reveal a strong influence of cerium on the SBN microstructure. The X-ray diffraction patterns show that all compositions of SBN ceramic exhibit tetragonal tungsten bronze structure. As the dopant concentration, y increased, both unit cell volume and axial ratio c/a decreased gradually. In addition, dopant incorporation lowers the phase transition temperature, T-m. As a result, all practical parameters are sufficiently increased, i.e. the dielectric constant and remnant polarization. SBN50 doped with a 3% Ce sample is most attractive for practical applications due to its high remnant polarization, P-r = 58.6 mu C/cm(2) and dielectric constant, epsilon ' approximate to 8000 (10 kHz) at room temperature, respectively. (C) 2016 Elsevier B.V. All rights reserved.

Metal–insulator–metal (MIM) capacitors based on lead titanate (PbTiO3) nanofilms were prepared using a novel method involving modified spin coating onto the bare electrodes of a coated glass. Different solutions were prepared by adding different concentrations of lead acetate (PbAc) powder to improve the electrical properties of the PbTiO3 films. The nanofilms were characterized in terms of their surface morphology, dielectric properties, and current–voltage characteristics. Physical and dielectric properties are related to the increased PbAc content in the films prepared within the range of 5–25 wt.%. The films with 10 wt.% PbAc provide acceptable dielectric permittivity, low loss factor, and improved capacitance density at frequencies lower than 100 kHz. Low leakage current densities and high resistivity behavior can be obtained at approximately 10−7 A cm2. Therefore, the resultant films are suitable for MIM capacitor applications and exhibit potential for memory storage applications.

Novel ferroelectric nanocomposite films with bismuth sodium titanate, Bi0.5Na0.5TiO3 (BNT), particles as fillers and polyvinylidenefluoride-trifluoroethylene, P(VDF-TrFE), copolymer as the matrix were prepared. The sol–gel method was used to synthesize the BNT nanopowder and spin coating was used to fabricate the nanocomposite films. The volume fraction of the BNT (∅) was in the range of 0.1–0.3. The structural, dielectric, pyroelectric, and ferroelectric properties of the samples were extensively investigated. Theoretical models, including Maxwell, Furukawa, Clausius–Mossotti, and effective medium theory (EMT), were employed to describe the effective dielectric permittivity of the composites. It is shown that the incorporation of BNT into the copolymer as a composite film significantly enhances the pyroelectric and ferroelectric properties. The P(VDF-TrFE)–BNT nanocomposite film with ∅=0.2 exhibits an exceptionally high remanent polarization of 115mC/m2 and pyroelectric coefficient of 50µC/m2K1. The figure of merit for detectivity FD is found to increase from 52 to 75µC/m2K1. The enhanced pyroelectric and ferroelectric properties obtained from this novel composite thin film strongly indicate the potential to apply this lead-free material as a thermal/infrared detector, energy storage, and micro-electromechanical system.

Strontium barium niobate (SBN) with the stoichiometric formula of SrxBa(1−x)Nb2O6 was synthesized using the solid-state reaction method. The compositions were varied as x=0.25, 0.30, 0.50, 0.51, 0.53, 0.55, 0.57 and 0.60 to identify the composition with the optimum structural and electrical properties. The structural properties of the SBN ceramic were studied using X-ray diffraction spectra, while the morphology of the sintered grain was monitored by a field emission scanning electron microscope (FESEM) measurement. The dielectric behavior and the main features of the diffuse phase transition of the SBN ceramics with relaxor behavior were carefully investigated. The increment of the x composition gives rise to continuous decrease of the temperature of the maximum dielectric constant. The effect of the diffuse phase transition and relaxation feature of the SBN can be attributed to the Sr2+ (variation of x composition) site distribution. The SBN ceramic with composition x=0.53 showed a saturated hysteresis loop at an applied field of 50 kV/cm, showing the highest remnant polarization of 8.17 μC/cm2 with a coercive field of ~11 kV/cm. The leakage current densities of the SBN samples were ranged between 0.1 and 1×10−5 A/m2 over a voltage range from 100 V to 6 kV. From these findings, the composition of x=0.53 gives the best electrical and structural properties compared to the rest of the compositions investigated and has potential application for practical lead free ferroelectric sensors.

Ferroelectric, pyroelectric and dielectric properties were investigated for Form IV poly(vinylidene fluoride) (PVDF). We fabricated highly crystalline Form II thin films by spin-casting from acetone or methyl ethyl ketone followed by annealing at 155 degrees C and then converted into Form IV using a high electric field of 500 MV/m. We observed displacement (D) - electric field (E) hysteresis loop and attendant pyroelectric activity that supported ferroelectric polarization reversal in Form IV PVDF. The highly rounded D-E loop with a coercive field of 240 MV/m suggests that reversal of the dipole component perpendicular to TGT (G) over bar chain requires very high field and progresses based on step-by-step switching of respective molecules. We also observed similar crystalline relaxations in Form II and IV suggesting that fluctuations of parallel dipoles in TGT (G) over bar chains were not affected by chain packing. Simultaneous observation of polarization reversal and dielectric relaxation associated with two orthogonal directions (a- and c-axis) of crystallites is interpreted using the tilt angle between of the chain axis and sample surface. Microscopic features are discussed in terms of electric-field-induced and thermally-induced changes in TGT (G) over bar conformational sequences. (C) 2015 Elsevier Ltd. All rights reserved.

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

A thin film of pyroelectric composite with 0-3 connectivity was fabricated from zinc oxide (ZnO) nanopowder and polyvinylidene fluoride (PVDF) with different volume fraction from 0-0.25 wt%. The dielectric and pyroelectric properties of the samples were investigated. It was found that the presence of a small amount of ZnO nanoparticles (0.25 wt%) has significantly increased the pyroelectric coefficient of the PVDF by 25%. Furthermore, the nanocomposite films required lower poling field to form polar-d phase compared to pure PVDF thin films. Analysis of the complex permittivity in a wide range of frequency was carried out indicating that the dielectric constant and loss of PVDF/ZnO nanocomposite thin films increase when doped with ZnO. Havriliak-Negami (HN) empirical function has been employed to obtain the alpha-relaxation time of the nanocomposite thin films before and after poling. The a-relaxation time does not vary with the increase of ZnO wt%; however, the effect of poling has lengthened the relaxation time of the thin films. FTIR and XRD results supports the fact that the addition of ZnO nanoparticles into PVDF polymer thin films do not cause any significant effect on the structure of the PVDF thin films. In fact, ZnO nanoparticle has enhanced the overall pyroelectricity of PVDF by facilitating the poling process in the composites and led to phase transformation of PVDF from alpha- to delta-phase as supported by a marked reduction of (100) x-ray diffraction intensities.

Glycolipid, found commonly in membranes, is also a liquid crystal material which can self-assemble without the presence of a solvent. Here, the dielectric and conductivity properties of three synthetic glycolipid thin films in different thermotropic liquid crystal phases were investigated over a frequency and temperature range of (10(-2)-10(6) Hz) and (303-463 K), respectively. The observed relaxation processes distinguish between the different phases (smectic A, columnar/hexagonal, and bicontinuous cubic Q) and the glycolipid molecular structures. Large dielectric responses were observed in the columnar and bicontinuous cubic phases of the longer branched alkyl chain glycolipids. Glycolipids with the shortest branched alkyl chain experience the most restricted self-assembly dynamic process over the broad temperature range studied compared to the longer ones. A high frequency dielectric absorption (Process I) was observed in all samples. This is related to the dynamics of the hydrogen bond network from the sugar group. An additional low-frequency mechanism (Process II) with a large dielectric strength was observed due to the internal dynamics of the self-assembly organization. Phase sensitive domain heterogeneity in the bicontinuous cubic phase was related to the diffusion of charge carriers. The microscopic features of charge hopping were modelled using the random walk scheme, and two charge carrier hopping lengths were estimated for two glycolipid systems. For Process I, the hopping length is comparable to the hydrogen bond and is related to the dynamics of the hydrogen bond network. Additionally, that for Process II is comparable to the bilayer spacing, hence confirming that this low-frequency mechanism is associated with the internal dynamics within the phase.

The different morphology of 250 nm PVDF-TrFE (70:30 mol%) thin films were observed in relation to its ferroelectricity. The annealing temperatures were varied from solvent evaporation (T-s), Curie's transition (T-c), up to melting temperature (T-m). It was found that the annealing process promoted the development of elongated crystallite structure also known as fen-oelectric crystal, which significantly improved the fen-oelectric properties of PVDF-TrFE (70:30 mol%) thin films However, the presence of nanoscale 'separations' on the thin film annealed over T-m (AN160) suggested high possibility of defects, and hence a reduction in ferroelectric properties of thin films.

Thin films of a ferroelectric polymer matrix made of poly(vinylidene fluoride) (PVDF) incorporated with a non-ferroelectric inclusion, TiO2, were prepared with different volume fractions (0-30 wt%). The dielectric and pyroelectric properties of the PVDF/TiO2 composite thin films are revealed as a function of different annealing temperatures (60 to 140 degrees C). Theoretical models, including Maxwell, Clausius-Mossotti, Furukawa and effective medium theory models were employed to describe the effective dielectric permittivity of the composites. This report also studies the effect of a non-ferroelectric inclusion, which contributed to the enhancement of pyroelectric activity after the poling process, in a ferroelectric polymer matrix based composite. An increase in the dc conductivity of the polymer matrix led to an easier poling process and reduced the required poling electric field from 260 to 120 MV m(-1). The pyroelectric coefficient of the polymer composite has been enhanced at a much lower poling electric field. The surface and structural properties of the thin film composites were also characterized by scanning electron micrographs, Fourier transform infrared spectroscopy and x-ray diffractometry.