High Field Poling Research Articles

Improvement of the piezoelectricity of PVDF-HFP by CoFe2O4 nanoparticles

High piezoelectric composite films composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and ferromagnetic cobalt ferrite (CoFe2O4) (0.00 ​wt% to 0.2 ​wt%) are prepared by a solution casting method accompanied by uniaxial stretching and high electric field poling. The decisive effect of the poling electric field on the power generating capability was confirmed by the experiments. For pure PVDF-HFP films, when the maximum electric field Emax is 120 ​MV/m, the calibrated open circuit voltage reaches 2.93 ​V, which is much higher than those poled at lower electric fields (70 ​MV/m: 1.41 ​V; 90 ​MV/m: 2.11 ​V). Furthermore, the addition of CoFe2O4 also influences the piezoelectricity dramatically. In the samples containing 0.15 ​wt% CoFe2O4, the calibrated open circuit voltage increases to the maximum value of 3.57 ​V. Meanwhile, the relative fraction of the β-phase and the crystallinity degree are 99% and 48%, respectively. The effects of CoFe2O4 nanoparticles on initial crystallization, uniaxial stretching and high electric field poling are investigated by XRD, FTIR and DSC.

The effect of domain switching on the lattice symmetry and dielectric properties of (Bi0.5Na0.3K0.2)TiO3–0.2SrTiO3-(Ba0.8Ca0.2)TiO3 piezo-ceramic by poling field

The present study illustrates the effect of domain switching on the structural, dielectric, and piezoelectric properties of [0.75(Bi0.5Na0.3K0.2)Ti O3-0.2SrTi O3-0.05(Ba0.8Ca0.2)Ti O3] (i.e., BNKT- ST-BCT) Pb-free ceramic caused by poling effect. The sample has been synthesized by the solid reaction technique. The poling conditions were changed from (10–50 kV/cm) for 30 min at 100 °C. The pristine ceramic sample showed pseudo-cubic crystal structure, while tetragonal structure was detected for all the poled samples. The pristine sample showed a normal ferroelectric loop with a low coercive field (Ec =12 kV/cm) owing to the domain grow caused by domain wall displacement. The effect of poling field into Raman spectra showed variation the volume fraction of orthorhombic and tetragonal phases. Increasing the intensity of the tetragonal phase is related to the increase in lattice symmetry of the poled samples at a high poling field. Relaxor to paraelectric phase transition was observed at Burn's temperature (TB) of the un-poled sample, while the poled rates undergo a ferroelectric to relaxor phase transition at depolarization temperature (Td). In the regime of the sub-switching domain, the maximum permittivity was found to increase by poling field due to Rayleigh effect, while at high poling field it was observed to decrease due to tunability effect. The maximum current peak of relaxor to ferroelectric phase transition was observed to mitigate by increasing the poling effect. The converse piezoelectric coefficient, (d33∗) was achieved to be higher in the un-poled sample due to the lowest crystal symmetry in the absence of a poling effect. The existence of poling process leads to shrink both current peak and (d33∗) values, indicating the dominated of the tetragonal phase rather than the orthorhombic phase. Such results offer distinct features of an un-poled ceramic sample that make it suitable for different technological applications such as energy storage devices, sensors, and actuators.

Nanoscale Activation Energy Mapping and Leveraging for Accelerating Ferroelectric Domain Nucleation and Growth

AbstractThe dynamics of ferroelectric domain switching are directly mapped in a PbZr0.2Ti0.8O3 thin film using piezoresponse force microscopy. Employing the rastering tip as a poling electrode to locally apply a fixed bias near the coercive field, while simultaneously monitoring the evolving domain pattern during continuous imaging, the effectively independent switching dynamics for numerous domains are directly investigated. While areal poling follows the anticipated S‐curve, this is shown to be the collective outcome of linear terminal radial growth for an ensemble of independently nucleating domains. By repeating such spatially resolved measurements in the same region, but with progressively greater fields, nucleation sites and growth patterns are shown to clearly repeat. This reveals apparent defects which comparatively promote switching, and nucleation times and growth rates that accelerate exponentially. After analyzing and mapping the ratio of activation energies for nucleation to growth, a high density of nucleation sites can possibly be activated with higher poling fields—even if only at the start of a poling process—enabling faster and more efficient switching to be engineered as directly demonstrated.

Bimodal polymorphic nanodomains in ferroelectric films for giant energy storage

Enhanced functional responses of ferroelectrics have often been achieved by complex compositional design of a morphotropic or polymorphic phase boundary. Here, we observe a pseudo-linear, ultra-slim polarization-electric field (P-E) hysteresis loop in simple composition, lead-free Ba(Zr,Ti)O3 of up to μm-thick. It features a low remnant polarization and a high maximum polarization after a delayed saturation process with a field-insensitive, thickness-scalable high energy efficiency of ∼90%. This giant energy storage performance is attributed to the self-assembled, bimodal polymorphic nanodomains consisting of two sets of coherent polymorphic nanodomains. The first set of domains has the best-matched, low index {110} interface. They manifest themselves as “entangled nanophases” and dominate in thinner or annealed films. The 2nd set of domains with a high-index {114} interface and an in-plane anisotropy leads to the largest reduction in bulk elastic energy. These domains show as “segregated nanophases” and prevail in as-grown thick films. The presence of multi-polar states in both sets of nanodomains helps reduce the remnant polarization and delay the polarization saturation. Furthermore, the segregated tetragonal phase in-plane nanodomains lead to a larger maximum polarization under a high poling field. Strain engineering of such nanodomain structures provides a promising alternative to chemical compositional design, for the optimization of dielectric thin films used in capacitive energy storage applications.

Enhanced Visible Photocatalytic Hydrogen Evolution of KN-Based Semiconducting Ferroelectrics via Band-Gap Engineering and High-Field Poling.

In various ferroelectric-based photovoltaic materials after low-band-gap engineering, the process by which high-field polarization induces the depolarizing electric field (Edp) to accelerate the electron-hole pair separation in the visible light photocatalytic process is still a great challenge. Herein, a series of semiconducting KN-based ferroelectric catalytic materials with narrow multi-band gaps and high-field polarization capabilities are obtained through the Ba, Ni, and Bi co-doping strategy. Stable Edp caused by high-field poling enhanced the visible photocatalytic hydrogen evolution in a 0.99KN-0.01BNB sample with a narrow band gap and optimal ferroelectricity, which can be 5.4 times higher than that of the unpoled sample. The enhanced photocatalytic hydrogen evolution rate can be attributed to the synergistic effect of the significant reduction of the band gap and the high-field-polarization-induced Edp. The change in the band position in the poled sample further reveals that high-field poling may accelerate the migration of carriers through band bending. Insights into the mechanism by which catalytic activity is enhanced through high-field-polarization-induced Edp may pave the way for further development of ferroelectric-based catalytic materials in the photocatalytic field.

Preparation of efficient piezoelectric PVDF–HFP/Ni composite films by high electric field poling

Abstract Poly(vinylidene fluoride) (PVDF) and its copolymers have been widely studied due to their excellent piezoelectricity and ferroelectricity. In this study, composite films are prepared by adding Ni nanoparticles (0.00–0.3 wt%) into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) matrix by solution casting, uniaxial stretching, and high electric field poling. It is found that when the maximum electric field E max for poling is 130 MV m−1, the calibrated open circuit voltage of the pure PVDF–HFP films reaches 3.12 V, which is much higher than those poled by a lower electric field (70 MV m−1: 1.40 V; 90 MV m−1: 2.29 V). This result shows that the effect of poling on the generated output voltage is decisive. By adding 0.1 wt% Ni nanoparticles, it increases to 3.84 V, 23% higher than that of the pure PVDF–HFP films. To further understand the enhancement mechanism, the effects of Ni nanoparticles on initial crystallization, uniaxial stretching, and high electric field poling are investigated by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and differential scanning calorimetry.

Visible-light photocatalytic hydrogen production in a narrow-bandgap semiconducting La/Ni-modified KNbO3 ferroelectric and further enhancement via high-field poling

The poled (1−x) KNbO3–xLaNiO3−δ ferroelectric semiconductors obtained an enhanced visible-light photocatalytic hydrogen evolution rate of 642.0 µmol g−1 h−1, which is at least 16 times that of the unpoled sample (40.1 µmol g−1 h−1).

Room temperature phase superposition as origin of enhanced functional properties in BaTiO3 - based ceramics

BaSnxTi1-xO3 (x = 0, 0.05) ceramics with orthorhombic/tetragonal phases at room temperature were comparatively investigated to understand the role of phase composition on their functional properties. With respect to the values of BaTiO3, the switching polarization, permittivity peak, tunability and piezoelectric coefficients are enhanced by doping with 5 % Sn onto Ti4+ sites. The orthorhombic polymorph amount is larger in the doped ceramic and explains its higher switching polarization. High field poling favors the orthorhombic phase in both compositions; this polymorph becomes predominant in the BaSn0.05Ti0.95O3 ceramic. Landau-based calculations developed for ceramics with randomly oriented grains predicted the stability of variable amounts of orthorhombic/tetragonal phases around room temperature and explain the field-induced predominant orthorhombic state, mostly in BaSn0.05Ti0.95O3. Due to the twelve allowed spontaneous polarization directions, the orthorhombic state is responsible for the enhanced polarization, tunability and piezoelectric properties with respect to the tetragonal state with six polarization possible orientations.

Electrical polarization phenomena, dielectric relaxations and structural transitions in a relaxor-ferroelectric terpolymer investigated with electrical probing techniques

Dielectric Relaxation Spectroscopy (DRS) and Thermally Stimulated Depolarization Current (TSDC) measurements were employed to study dielectric-relaxation processes, structural transitions and electric-polarization phenomena in poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films. Results from DRS confirm the existence of two separate dispersion regions related to a para-to-ferroelectric phase transition and to the glass transition. The dipolar TSDC peak correlates with the loss peak of the α relaxation that represents the glass transition. The electric polarization calculated from the dipolar TSDC peak (glass transition) shows a non-linear electric-field dependence and saturates at high electric poling fields. As the observed behaviour is essentially the same as that of the electric polarization obtained from direct polarization-versus-electric-field hysteresis measurements, TSDC experiments are also suitable for studying the polarization in relaxor-ferroelectric polymers. A saturation polarization of 44 mC m−2 was found for an electric field of 190 MV m−1.

Nature of Ferroelectric Behavior in Main-Chain Dipolar Glass Nylons: Cooperative Segmental Motion Induced by High Poling Electric Field

Main-chain dipolar glass polymers such as aromatic nylons are promising for high energy density and low loss dielectric applications because of the limited, noncooperative oscillation of highly dipolar amide groups. However, quenched aromatic nylons have been reported to exhibit significant ferroelectric switching upon high field poling. It is desirable to suppress ferroelectric switching for electric energy storage application, and this requires a fundamental understanding of the nature of ferroelectric behavior in dipolar glass nylons. In this work, a nearly 100% amorphous aromatic nylon, Selar, was used to investigate the origin of ferroelectricity in glassy nylons. Using Fourier transform infrared spectroscopy, it was found that hydrogen-bonding strength played an important role in the ferroelectric switching of amide dipoles in the loosely packed glassy matrix. When hydrogen bonding was weak such as in the quenched film, significant ferroelectric switching took place. In contrast, quenched and anneal...

Significant triboelectric enhancement using interfacial piezoelectric ZnO nanosheet layer

Utilising an interfacial piezoelectric ZnO nanosheet layer, a significant enhancement in the power density is reported for the triboelectric nanogenerators (TENG) based on phase inversion membranes of polyvinylidene fluoride (PVDF) and polyamide-6 (PA6). At an applied force of 80N, the TENG device incorporating electrochemically deposited ZnO nanosheets produces an output voltage of ~ 625V and a current density of ~ 40mAm−2 (corresponding a charge density of 100.6μCm−2), respectively; significantly higher than ~ 310V and ~ 10mAm−2 (corresponding a charge density of 77.45μCm−2) for the pristine TENG device. The enhancement in the surface charge density provided by the interfacial piezoelectric ZnO layer is also reflected in the high piezoelectric coefficient d33 (−74pmV−1) as compared to the pristine fluoropolymer membranes (−50pmV−1). For tribo-negative membranes incorporating the interfacial ZnO layer, piezoelectric force microscopy measurements further show enhanced domain size which can be attributed to the interfacial dipole-dipole interaction with the ferroelectric polarisation of PVDF, which promotes the alignment with the polar axis of ZnO. Under compressive stress, the piezoelectric potential thus produced in the ZnO nanosheets provides charge injection on to the surface of ZnSnO3-PVDF membrane, improving the charge density, which in-turn significantly enhances the power density from 0.11 to ~ 1.8W/m2. The TENG devices thus fabricated using a facile electrochemical deposition and phase inversion technique show enhanced output power without the need for high electric field poling or external charge injection process by relying on the coupling of triboelectric and piezoelectric effects.

The Role of Field Electron Emission in Polypropylene/Aluminum Nanodielectrics Under High Electric Fields.

Polymer/metallic particle nanocomposites or nanodielectrics can exhibit colossal dielectric constants with a relatively low dissipation factor under low electric fields and thus seem to be promising for high-energy density dielectric capacitors. To study this possibility, this work focused on the dielectric performance and loss mechanisms in polypropylene (PP)/aluminum nanoparticle (nAl NP) composites under high electric fields. Phosphonic acid-terminated poly(ethylene-co-1-butene) was grafted to the Al2O3 surface layer on the nAl NPs in order to achieve reasonable dispersion in the PP matrix. The dielectric breakdown study showed that the breakdown strength decreased to nearly 1/20 that of the neat PP film as the nAl content increased to 25.0 vol %. The leakage current study revealed three electronic conduction mechanisms in the PP/100 nm nAl nanocomposites, namely, ohmic conduction at low fields, hopping conduction at intermediate fields, and Fowler-Nordheim (FN) field electron emission above a critical field, depending on the filler content. Compared to the 100 nm nAl NPs, smaller (e.g., 18 nm) nAl NPs needed a much higher electric field to exhibit FN field electron emission. It was the FN electron tunneling that induced a substantial reduction in breakdown strength for the PP/nAl nanocomposites. Meanwhile, electron-tunneling injected space charges (electrons) from nAl NPs into the PP matrix, and internal electronic conduction led to significant dielectric nonlinearity at high poling fields. Although polymer/metallic NP composites are not suitable for high-field electric applications, they can be good candidates for electrical switches and quantum tunneling composites operated at relatively low electric fields.

Mechanism that governs the electro-optic response of second-order nonlinear polymers on silicon substrates

We use a modified Teng-Man technique to investigate the poling induced electro-optic activity of chromophore-doped organic polymers poled on silicon substrate in a thin film sample configuration. We reveal a fundamental difference between the poling processes on silicon substrate and ITO substrate. The electro-optic activity for polymers poled on silicon substrate is reduced which we ascribe to space charge formation at the silicon - organic interface that distorts the field distribution in the polymer film during high field poling, and therefore limits the effective induced polar order. We demonstrate that the electro-optic activity on silicon substrate can be improved by inserting a 5 nm thin dielectric layer of Al2O3 between the silicon substrate and the polymer which reduces the leak-through current during poling, thereby allowing for higher applicable poling voltages.

Unique single-domain state in a polycrystalline ferroelectric ceramic

Non-180\ifmmode^\circ\else\textdegree\fi{} ferroelectric domains are also ferroelastic domains; their existence in polycrystalline materials is to relieve internal stresses generated during solid-solid phase transitions and minimize the elastic distortion energy. Therefore, grains with random orientations in polycrystalline ceramics are always occupied by many domains, especially in the regions close to grain boundaries. In this Rapid Communication, we report the observation of a single-domain state in a BaTiO${}_{3}$-based polycrystalline ceramic at intermediate poling electric fields with in situ transmission electron microscopy. The grains in the virgin ceramic and under high poling fields are found multidomained. The unique single-domain state is believed to be responsible for the ultrahigh piezoelectric property observed in this lead-free composition and is suggested to be of orthorhombic symmetry for its exceptionally low elastic modulus.

A Fast Room-Temperature Poling Process of Piezoelectric Pb(Zr<SUB>0</SUB><SUB>.45</SUB>Ti<SUB>0</SUB><SUB>.55</SUB>)O<SUB>3</SUB> Thin Films

The effect of two poling processes on the ferroelectric and piezoelectric properties of sol–gel and pulsedlaser-deposited Pb(Zr0.45Ti0.55)O3 (PZT) thin films has been investigated as a function of the poling field, poling temperature and poling time. In the case of dc-electric field poling at an elevated temperature (200 °C), the remnant polarization and effective piezoelectric coefficient are found to increase with and saturate at high dc-poling field (400 kV/cm) and long poling time (30 minutes). The room-temperature poling process using ac electric field poling, shows the same trend with poling field but much shorter poling times (100 seconds), with only a slightly lower saturation value of polarization. It is suggested that in room-temperature poling screening charges are merely rearranged, whereas in high temperature poling these charges are largely removed. A much larger improvement in the properties of sol–gel PZT thin films is found, as compared to those deposited using pulsed laser deposition (PLD), indicating that a poling process is required for sol–gel films.

Highly Efficient Organic Electrooptic Materials and Their Hybrid Systems for Advanced Photonic Devices

This review summarizes recent development of highly efficient organic electricoptic (OEO) materials and their applications in hybrid photonic devices. New generation of highly efficient EO polymers possessing large Pockels coefficients of 200-250 pm/V at 1.3 μm and excellent thermal and photochemical stability have been developed for advanced photonic devices. In addition, new pyroelectric poling process provides an efficient and reliable high field poling for EO polymers in multilayered thin films and nanophotonic waveguides. Using OEO materials as a key enabling element, significant progress has been made in the development of innovative hybrid EO devices, including EO polymer hybrid nanophotonic waveguides with high-index semiconductors, all polymer- and polymer/sol-gel-based EO modulators using low-refractive-index cladding layers, and EO polymer-based electric field sensors. At the end, this review also provides an outlook of future development of OEO materials and their hybrid systems for advanced photonic technologies.

In Situ X-ray Diffraction of Biased Ferroelastic Switching in Tetragonal Lead-free (1−x )Ba(Zr0.2 Ti0.8 )O3 -x (Ba0.7 Ca0.3 )TiO3 Piezoelectrics

The effect of electric poling on the bipolar switching for tetragonal BZT–BCT materials is studied using large signal polarization and strain, small signal permittivity, and piezoelectric coefficient, as well as electric field–dependent in situ XRD experiments. Charge carrier agglomeration at domain and grain boundaries with increasing poling fields gives rise to an internal bias field that gradually biases domain switching behavior. The biased switching after electric poling is quantified during a bipolar measurement cycle from analysis of the electric and structural data. For a fresh sample the ferroelastic domain texture induced by a positive and negative electric measurement field is of the same magnitude. After poling, the induced ferroelastic domain texture is larger under a positive measurement field and smaller under a negative measurement field. A very large domain texture is achieved during poling, corresponding to 85% of the domains becoming aligned with their 002 pole in field direction. While the domain texture is significantly improved at higher poling fields, relaxation upon removal of the electric field appears independent of the poling history. This suggests a large extrinsic contribution to the macroscopic strain. It also facilitates the biased ferroelastic switching arising from the internal bias field developed during poling.

Photo-induced denitrogenation of triazoline moieties for efficient photo-assisted poling of electro-optic polymers

Efficient room temperature poling of a guest–host electro-optic (EO) polymer is achieved by photo-induced denitrogenation of triazoline moieties. The host polymer (P1) with Δ2-1,2,3-triazoline groups on the backbone is synthesized by 1,3-dipolar cycloaddition polymerization between a bis-N-phenylmaleimide and an aromatic bis-azide. The guest chromophore (C1) is a push–pull compound with a strong dialkylaminophenyl donor and a CF3–TCF acceptor. By irradiating the thin films of P1 with a compact UV lamp at 365 nm, the angular and asymmetric 1,2,3-triazoline structures can be readily converted into a more straight and symmetrical aziridine structure by losing nitrogen. This photo-induced denitrogenation provides the clean conversion to form an aziridine-based polymer P2. This high efficiency conversion process is insensitive to the light-absorbing nonlinear optical chromophores, and the reaction rate can be controlled by the irradiation power and the thin film UV absorbance. Upon the photo-induced denitrogenation, considerable structural change of the polymer backbone provides sufficient rotational freedom to the chromophores for the poling of EO polymers. This has been verified by the demonstration of high field poling (up to 250 V μm−1) and large EO activity at RT for thin films containing 20–25 wt% of chromophore C1 in P1, which can be efficiently activated by photochemical denitrogenation of triazoline moieties by irradiating with low-power UV light.

Fabrication and Characterization of Dielectric Nanocube Self-Assembled Structures

Orderly assemblies of BaTiO3 (BT) cube-shaped nanocrystals (nanocubes) and BT–SrTiO3 (ST) mixture nanocubes were fabricated on Pt-coated Si substrates directly by capillary-force-assisted solution self-assembly and heat treatment. These dielectric nanocubes aligned face to face in quite a wide region of 10×50 µm2 on the average with a height of 1 µm. The local microstructure of the nanocube assembly was observed by high-resolution transmission electron microscopy. It was revealed that the lattice strain at the interface of the neighboring nanocubes was locally induced. The piezoresponse of the BT–ST mixture nanocube assembly showed a nonlinear curve and a stepwise behavior at a high poling field, which differed from the ferroelectric BT and paraelectric ST assemblies investigated by scanning probe microscopy. The characteristic behavior might be attributed to the interfacial lattice strain in mixture assemblies.

Piezoresponse properties of orderly assemblies of BaTiO3 and SrTiO3 nanocube single crystals

Orderly assemblies of BaTiO3 (BT) nanocubes, SrTiO3 (ST) nanocubes and BT-ST mixture nanocubes were fabricated on Pt-coated Si substrate directly by solution self-assembly and heated at 850 °C. The dielectric nanocubes aligned face to face in a quite wide region of several tens of square-micrometers with a height of one micrometer, and even inside of the structures was ordered. The piezoresponse of BT-ST mixture assembly showed non-linear curve and stepwise behavior at high poling field, which differed from ferroelectric BT and paraelectric ST nanocube assemblies.