Large Dielectric Strength Research Articles

Energy storage properties, transmittance and hardness of Er doped K0.5Na0.5NbO3-based ceramics

Transparent energy storage ceramics can balance energy storage characteristic and optical characteristic, and are expected to be used in areas such as transparent pulse capacitors. However, excellent energy storage performance and dramatic light transmittance are difficult to achieve simultaneously, limiting their subsequent development in the actual applications. The paper proposes a way to improve the transparent energy storage properties of KNN-based samples by regulating domain and grain size. By introducing an appropriate amount of Er2O3, fine cube grains and nanodomains are constructed. When doping 0.20 mol% Er2O3, the ceramics exhibited excellent recoverable energy storage density Wrec ∼ 6.2 J/cm3, superior energy-storage efficiency η ∼ 71.3 %, large dielectric breakdown strength Eb ∼ 670 kV/cm, ultrahigh hardness value of 6.9 GPa, and a maximum transmittance T ∼72 % at 880 nm. Dense microstructure, nanoscale grains, symmetrical lattice structure and relaxor behavior are the main reasons for obtaining high energy storage and transparency properties.

Interfacial insight of core@double‐shell Mo@MoO3@PS/PVDF composites towards prominently meliorative dielectric performances

AbstractPolymer dielectrics with synergistically large dielectric permittivity (ε') and breakdown strength (Eb) but prohibited loss is of crucial applications in the electronic devices and power equipment. In this study, we aim to elevate the integrated dielectric performances of molybdenum (Mo)/polyvinylidene fluoride (PVDF) by constructing a semiconducting molybdenum oxide (MoO3) shell and insulating polystyrene (PS) shell on the Mo surface through high‐temperature oxidation followed by suspension polymerization. The resulting core@double‐shell Mo@MoO3@PS particles were compounded with PVDF to achieve high ε' and Eb while minimizing the loss. The results reveal that the Mo@MoO3@PS/PVDF composites indicate simultaneously ameliorative ε' and Eb along with restrained loss owing to the existence of the MoO3@PS double‐shell, which not only prominently enhances the interfacial compatibility and interactions between fillers and PVDF, but significantly inhibits the conductivity and loss through impeding the long‐distance motion of carrier charges. The dielectric capabilities could be improved by adjusting the thickness of the PS interlayer. The Havriliak‐Negami equation was used to fit the experimental results, which showed the impact of the PS shell on the polarization mechanism and how it inhibits carrier migration. The Mo@MoO3@PS/PVDF with high ε' and Eb yet exceptionally low loss exhibit potential applications in microelectronics and electrical industries.

Simultaneously realizing ultrahigh energy storage density and efficiency in BaTiO3-based dielectric ceramics by creating highly dynamic polar nanoregions and intrinsic conduction

Nowadays, it is urgent to explore advanced and eco-friendly energy storage capacitors based on lead-free relaxor ferroelectric (RFE) ceramics in order to meet the ever-increasing requirements in pulsed power systems. BaTiO3 (BT)-based RFE ceramics are considered as ones of the best high-temperature energy storage materials due to their good thermal stability. However, relatively low recoverable energy storage density (Wrec<5 J/cm3) has been a key bottleneck restricting the practical applications of them. Here, a novel strategy is proposed to create highly dynamic PNRs and the intrinsic conduction by introducing Bi(M1-0.015xTa0.015x)O3+0.015x (BMO-Ta, M=Mg2/3Ta1/3) to BT matrix. As a consequence, the designed (1-x)BT-x(BMO-Ta) ceramics exhibit dramatically enhanced energy storage properties including ultrahigh Wrec and efficiency (η), because of the coexistence of very slim polarization hysteresis (P-E) loops, large polarization difference (ΔP) and giant dielectric breakdown electric strength (Eb). Wrec and η of the x=0.25 ceramic reach up to 9.03 J/cm3 and 95.2% under 720 kV/cm, respectively. Furthermore, it shows excellent temperature/frequency/cycling stability over a wide range of 20−200 °C, 1−500 Hz and 1−3.3 × 105 cycles, respectively (the variations of Wrec and η are < 3% and < 4%, respectively). The findings in this paper not only indicate excellent comprehensive properties achieved in the novel (1-x)BT-x(BMO-Ta) system, but also provide an effective approach to explore advanced energy storage capacitors in other lead-free ceramic systems.

(Invited, Digital Presentation) Yet Another Symmetry Breaking in Electromechanical Materials

The wide range of fascinating properties observed in complex oxide continue to attract great interest such as ferro-, piezo- and pyroelectricity. Several strategies have been employed to break the lattice symmetry and expand the range of functionalities. Electrostriction is a general property of all dielectrics and occurred when the deformation of a dielectric material is proportional to the square of the applied electric field. Recently, Gd2O3-doped CeO2 (CGO) has emerged as a new family of electrostriction materials with the maximum stress exceeding 500 MPa. To date, various efforts have been made to improve the strain output, such as stimulate by electric field, varying the temperature and aging the defects. However, materials that simultaneously satisfy the requirements of fast response, large strain and high energy density are still very rare. The development of materials with large dielectric breakdown strength, high dielectric constant and low elastic modulus is still challenging.Heterostructure interfaces plays an important role by contributing to its unique structural and physical properties which result in symmetry breaking, electronic and/or atomic reconstruction(s) as well as strain gradients from which a wealth of new intriguing properties can emerge. Such richness arises from a strong interaction between the charge, orbital, spin, and lattice degrees of freedom.Here, I will show how symmetry breaking offers extraordinary opportunities such as stabilizing phases which are otherwise not stable using highly coherent interfaces and enhancing the electromechanics with interfaces or inducing piezoelectricity in otherwise centrosymmetric system. In one example I will show the results obtained with a stack of ultrathin defective oxide single-crystal layers with stable phases and electrostriction properties exceeding any known system. Alternating layers of Gd2O3-doped CeO2 (CGO) and Er2O3-stabilized δ-Bi2O3 (ESB) were deposited on NdGaO3 substrates. The measured electrostriction coefficients found to follow a linear increase with the decrease of the number of interfaces. We have observed the highest electrostriction coefficient which surpasses any known electrostrictive materials, including the commercial relaxor ferroelectrics, such as PMN-PT. In another examples I will show our recent discovery illustrating the possibility to induce a large piezoelectric response in centrosymmetric oxides, i.e., in cubic fluorite oxides, Gd-doped CeO2-x. Surprisingly, the results show the generation of large low-frequency piezoelectric responses (d33 ~ 100,000 pm/V). Such a high piezoelectric response from intrinsically nonpiezoelectric materials has not been observed before in centrosymmetric materials.This collection of possibilities offers unique opportunities for a wide range of rich world and new functionality of complex oxide and their interfaces.

Electric Switching Behaviors and Dielectric Relaxation Properties in Ferroelectric, Antiferroelectric, and Paraelectric Smectic Phases of Bent-Shaped Dimeric Molecules.

This study reports the electric switching behaviors and dielectric properties of the ferroelectric smectic-A (SmAPF), anti-ferroelectric smectic-A (SmAPA), anti-ferroelectric SmCAPA, and smectic-A (SmA) phases formed by mixing the bent-shaped dimeric molecules, α,ω-bis(4-alkoxyanilinebenzylidene-4'-carbonyloxy)pentanes. These four phases each show characteristic features. The SmAPF shows a low threshold electric field for ferroelectric switching and a large dielectric strength due to the collective fluctuation mode of dipoles at around 500 Hz. Both the threshold electric field and dielectric strength are strongly dependent on the cell thickness. The threshold field decreases to 0.1 V μm-1, and the dielectric strength increases up to a huge value of 10,000 as the cell thickness increases up to 80 μm. The SmAPA also shows a similar collective mode at around 2 kHz with a relatively small dielectric strength (around 200), which may be induced by the anti-phase rotation of dipoles in adjacent layers. In these collective modes, the dielectric strength is found to be inversely proportional to the switching threshold field. On the other hand, another anti-ferroelectric SmCAPA as well as the paraelectric SmA show only the non-collective mode (i.e., rotational relaxation of individual molecules around their short axes) at a high frequency of around 100 kHz.

Synthesis of polar polynorbornenes with high dielectric relaxation strength as candidate materials for dielectric applications.

Materials with high dielectric permittivity and dielectric relaxation strength are sought for thermal and pressure sensors and electrical energy generators. However, most polymers have either too low dielectric permittivity or are so polar that their glass transition temperature (Tg) is too high and thus decomposition and side reactions occur before an electric field can polarize the polar groups. Here, we use the power and versatility of ring-opening metathesis polymerization (ROMP) to synthesize polar polymers with high dielectric relaxation strength and Tg significantly below the decomposition temperature. We first synthesized six polar norbornene monomers by conventional esterification, which were then polymerized by ROMP using Grubbs first- and third-generation catalysts. The structure of the polynorbornenes obtained were verified by multinuclear NMR spectroscopy, molecular weights determined by gel permeation chromatography (GPC), and thermal properties evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Additionally, their dielectric permittivity, conductivity, and dielectric losses were measured at different temperatures and frequencies ranging between 0.1 and 106 Hz.

Voltage Control of Perpendicular Magnetic Anisotropy in Multiferroic Composite Thin Films under Strong Electric Fields.

"Ferroelectric/ferromagnetic" multiferroic composites with perpendicular magnetic anisotropy (PMA) are useful for developing power-efficient magnetic memories. Voltage control of PMA has been demonstrated in bulk multiferroic composites based on ferroelectric single crystals, but they are not compatible for integration. Multiferroic composite thin films are useful for developing integrated devices; however, voltage control of PMA in them has not been achieved yet at room temperature due to their low magnetoelectric (ME) coupling coefficient. Here, we demonstrate such functionality and propose to enhance their ME coupling effect under a strong electric field by taking full advantage of the large dielectric strength of ferroelectric thin films. First, the thickness-dependent breakdown of Pb(Zr0.384Ti0.576Nb0.04)O3 (PNZT) thin films was studied, and the two-layer (∼200 nm) samples exhibited the highest breakdown strength (3.68 MV/cm) and small surface roughness (<1 nm). Second, we fabricated "PNZT/(Co/Pt)5" thin films with strong PMA whose breakdown strength is nearly independent of the top electrode materials. Finally, voltage-induced effective magnetic field (Heff) in "PNZT/(Co/Pt)5" was studied. It is comparable to that achieved in bulk composites and will induce magnetization switching under strong electric fields. Multiferroic composite thin films with large breakdown strength will provide a useful platform for enabling integrated multiferroic devices.

Thermal, mechanical and dielectric properties of functionalized sandwich BN-BaTiO3-BN/polypropylene nanocomposites

Research attention has been drawn towards the development of polypropylene (PP) based materials, which simultaneously have large dielectric constant, mechanical strength, and thermal stability for power-related applications. This study achieved that by using sandwich structured BN-BaTiO3-BN in modification of PP matrix. The BN-BaTiO3-BN sandwich nanoparticles were prepared via hydrothermal and assembly techniques. Before that, the nanoparticles were surface functionalized using 3-glycidoxypropyltrimethoxysilane. The functionalized nanoparticles were investigated using FTIR and TGA, which confirmed successful functionalization. Molten polypropylene grafted maleic anhydride (PPMA) compatibilizer was used to wrap the BN and BaTiO3 (BT) nanoparticles, which also promoted their compatibility with the PP matrix. The nanocomposites were prepared via melt compounding method using rheomixer. The developed PP nanocomposites showed enhanced DSC properties and thermal stability (above 20 °C compared to the pure PP). In addition, the dielectric constant increased from 2.02 at 100 Hz for the pure PP to 4.68 for PP/5BN-15BT nanocomposite, which is about 132% increase. The nanocomposite also retained an appreciable low loss of about 0.05 at 100 Hz. The enhanced dielectric and thermal properties are required for optimal performance of PP dielectric film capacitor for power applications and miniaturization of electronic components. The various improved properties were attributed to interfacial polarization, interlocking of PP chains and thermal barriers in the PP matrix offered by the nanoparticles.

Fabrication and dielectric performance of RGO-PANI reinforced PVDF/BaTiO3 composite for energy harvesting

Today’s techno savvy world demands smart devices which are light-weight, flexible, and scalable. Functional polymers and their composites are suitable candidates that can fulfill the requirements in flexible device applications. Polyvinylidene fluoride (PVDF) is one kind of functional polymers possessing a large dielectric strength as well as permanent electrical dipole. To improve the dielectric and ferroelectric performance of the PVDF polymer, it can be hybridized with an inorganic/organic inclusion phase, usually ferroelectric ceramic particles or nano-sized low dimensional carbon. In this work, reduced- graphene oxide (RGO) and RGO-PANI were chosen as the inclusion phase (filler). The present work focuses towards enhancing the dielectric and ferroelectric properties of PVDF-BaTiO3 (P/BT) nanocomposites impregnated with RGO and RGO/PANI(Polyaniline) nanofillers. In-situ polymerization method was adapted to fabricate the RGO/PANI nanocomposite and spin coating method for P/BT composites. X-ray diffractograms and FTIR corroborate the presence of ferroelectric phases in P/BT matrix. Wayne Kerr precision impedance analyzer was used in the frequency frame of 1 Hz to 1 MHz and temperature window from 30 °C to 160 °C to study the dielectric properties. The P-E hysteresis loops were obtained using Radiant Ferroelectric Tester at different voltage cycles. The dielectric constant of P/BT matrix with 0.03% RGO loading exhibited the highest dielectric constant 2 × 105. Remarkable increase in the energy density of composites with filler loading was observed. P/BT with 1 wt% loading of RGO-PANI achieved the maximum value of polarization 3.6 µC/cm2 and discharge energy density 0.76 J/cm3 (under the electric field of 170 kV/cm) with 55% efficiency. This contribution provides a potential route to design and fabricate high energy density flexible capacitor for microelectronic devices.

Enhanced recoverable energy density of 0.94Bi0.50(Na0.78K0.22)0.50Ti1−x(Fe0.50Nb0.50)xO3–0.06BaZrO3 lead-free relaxor ceramics doped by (Fe0.50Nb0.50)4+ complex ions

The innovative 0.94Bi0.50(Na0.78K0.22)0.50Ti1−x(Fe0.50Nb0.50)xO3–0.06BaZrO3 (BNKTBZ-xFN) lead-free relaxor ceramics were designed and fabricated by the conventional solid-state technique. The dielectric, ferroelectric, energy storage, and impedance performance of these ceramics were investigated systematically. XRD patterns revealed that the (Fe0.50Nb0.50)4+ complex ions had completely dissolved in the lattice and constructed a single solid-solution. The addition of (Fe0.50Nb0.50)4+ complex ions had an obvious impact on the grain size and crystallinity of BNKTBZ-xFN ceramics, which led to a large dielectric breakdown strength. In addition, the degree of diffusivity (γ) for BNKTBZ-xFN ceramics were increased from ~ 1.72 to ~ 1.93, indicating an enhanced relaxor behavior with the doping of (Fe0.50Nb0.50)4+ complex ions. The highest recoverable energy density (Wrec) ~ 1.20 J/cm3 and energy-storage efficiency (η) ~ 72% were attained at 120 kV/cm for BNKTBZ-2FN ceramic with the excellent fatigue resistance. Therefore, the BNKTBZ-2FN ceramic might be a promising candidate for energy-storage electronic devices.

Cross-Plane Thermal Conductance of Phosphonate-Based Self-Assembled Monolayers and Self-Assembled Nanodielectrics.

Self-assembled nanodielectrics (SANDs) consist of alternating layers of polarized phosphonate-functionalized azastibazolium π-electron (PAE) and high-k dielectric metal oxide (ZrO2 or HfOx) films. SANDs are desirable gate dielectrics materials for thin-film transistor applications because of their excellent properties such as low-temperature fabrication, large dielectric strength, and large capacitance. In this paper, we investigate the cross-plane thermal boundary conductance of SANDs using the frequency domain thermoreflectance (FDTR) technique. First, we characterize the thermal conductance of PAE self-assembled monolayers (SAMs), inverted-PAE (IPAE) SAMs, and mixed PAE-IPAE SAMs, sandwiched between thin gold and silica (SiO2) films at the top and bottom surfaces. Next, we quantify the thermal conductance of SAND-n with different numbers (n) of PAE-ZrO2 layers and thicknesses ranging between 4.7 and 11.3 nm. From the FDTR measurements, we observe that the thermal boundary conductance of the SAMs can be tuned between 42.1 ± 4.6 MW/(m2 K) and 52.4 ± 2.5 MW/(m2 K), based on the relative density of the PAE and IPAE chromophores. In the SAND-n samples, we observe a monotonic decrease in the thermal conductance with increasing n. We use the measured thermal conductance data in a series resistance model to estimate a thermal interface conductance of 695 MW/(m2 K) for the contact between the PAE chromophore and the zirconium dioxide films, which is an order of magnitude larger than the SAMs. We attribute the improved thermal conductance to stronger adhesion between the PAE chromophore and the zirconium dioxide films, as compared to the weakly bonded SAMs to the gold and silicon dioxide films.

Formation mechanism, dielectric properties, and energy-storage density in LiNbO3-doped Na0.47Bi0.47Ba0.06TiO3 ceramics

The development of ferroelectric (FE) ceramics with high recoverable energy-storage density (Wrec) critically affects the miniaturization and integration of advanced pulse-power capacitors. However, most lead-free FE materials have the shortcomings of large remanent polarization and low dielectric breakdown strength. In this work, a strategy of composition control was implemented to improve the Wrec of lead-free ceramics. The effects of Li and Nb ion incorporation on the structure, dielectric, and ferroelectric properties of the highly insulating (Na0.5Bi0.5)TiO3–BaTiO3 (NBT–BT) ceramic was investigated. X-ray diffraction analysis of the samples revealed that the pure phase was isostructural to (Na0.5Bi0.5)TiO3. Dielectric measurements exhibited two pronounced anomalies which shift a certain angle within the depolarization-temperature range. The effects of LiNbO3 content on the breakdown characteristics and discharge energy storage of NBT–BT ceramics were investigated. An enhanced discharged energy density of 1.05 J/cm3, calculated from a hysteresis loop, was observed at x = 4 mol%. The improved structure also resulted in an increase of up to 61% in breakdown strength.

Enhanced energy storage density and discharge efficiency in potassium sodium niobite-based ceramics prepared using a new scheme

The development of lead-free ceramics with high recoverable energy density (Wrec) and high energy storage efficiency (η) is of great significance to the current energy situation. In this work, a new scheme was proposed to improve the Wrec and η of potassium sodium niobate ((K, Na)NbO3, abbreviated as KNN) lead-free ceramics. Doping Bi elements in KNN ceramics to form a second phase (K2BiNb5O15) can reduce the grain size and form Schottky-like contact. Meanwhile, the hybridization between the Bi 6p and O 2p orbitals can enhance the maximum polarization (Pmax). So the K1-3xBixNa0.5NbO3-1 mol%CuO ceramics was proposed to improve the Wrec of lead-free ceramics. A large Wrec (2.89 J/cm3) and dielectric breakdown strength (DBS) (300 kV/cm with a thickness of 0.2 mm) were achieved for K0.14Bi0.12Na0.5NbO3-1 mol%CuO ceramics. The high Wrec was supposed to benefit from low remnant polarization (Pr), high Ps and DBS of ceramics. In addition, a large η (80%) was simultaneously achieved for K1-3xBixNa0.5NbO3-1 mol%CuO ceramics, which is superior to mostly reported lead-free bulk ceramics. The results show that K1-3xBixNa0.5NbO3-1 mol%CuO ceramics have a good application prospect in the field of energy storage, and provide a new scheme for the preparation of lead-free ceramics with high energy storage density and high conversion efficiency.

A high-tolerance BNT-based ceramic with excellent energy storage properties and fatigue/frequency/thermal stability

A novel perovskite lead-free solid solution of (Ba0.06Bi0.47Na0.47)1-xLaxTi1-yZryO3 were designed by dual-substitution of La3+ and Zr4+ for (Ba0.06Bi0.47Na0.47)2+ and Ti4+. The frequency-, temperature- and fatigue-dependent energy storage properties of the materials were investigated. After the dopings of La3+ and Zr4+, the crystal structure of the ceramics remains unchanged; and tetragonal and rhombohedral phases coexist in all ceramics which exhibit a relaxor phase transition. The co-substitution of La3+ and Zr4+ leads to the high dielectric breakdown strength (DBS), large spontaneous polarization (Ps) and small remnant polarization (Pr) of the materials. The optimum energy storage properties are achieved at x/y = 0.02/0.04, giving high recoverable energy storage density of Wrec ~1.55 J/cm3, excellent energy storage efficiency of ƞ ~72.6% and large dielectric breakdown strength of DBS ~136 kV/cm. Furthermore, the ceramic with x/y = 0.02/0.04 possesses superior durability of frequency (~2–60 Hz), fatigue (~ 103) and temperature (~ 25–245 °C).

Giant electrical energy storage density in the P(VDF-TrFE)–graphene oxide composite papers with quasi-two-dimensional ferroelectricity

The nanocomposites consisting of graphene oxide (GO) and ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] have been successfully synthesized by a co-evaporation method. The structural, dielectric and ferroelectric properties of the composite papers are investigated. The Raman spectroscopy analyses on the nanocomposites GO/P(VDF-TrFE) reveal that the defects in GOs are reduced significantly by the loading of ferroelectric P(VDF-TrFE). The IG/ID ratio increases from 1.02 (for pure GO) to 1.17 [for GO/P(VDF-TrFE)-10%], revealing that the defects are reduced by the introduction of the nano-fillers due to a strong interaction between GO and P(VDF-TrFE) in the nanocomposites. The permittivity of the nanocomposites is enhanced by almost 3-times as compared to that of the pristine GOs. The nanocomposites show a notably raised polarization with high applied electric field. Furthermore, due to the high dielectric constants, the electrical energy storage density of the nanocomposites is as high as ~ 39.89 J cm−3 at 2.8 MV cm−1. The large energy density and high dielectric break down strength suggest that GO/P(VDF-TrFE) could be the promising novel materials for electrical energy storage.

Design and Application of Integrated Optics Sensor for Measurement of Intense Pulsed Electric Field

Integrated optical waveguide sensor has characteristics of good insulation, broadband response, small size, and large dielectric strength, which is appropriate for measurement of intensive pulsed electric field. Two types of integrated optics sensors using through and reflective type asymmetric Mach–Zehnder interferometer are designed, fabricated, and implemented. Key parameters of the optical waveguide and antenna are theoretically analyzed and designed. The time domain response, input/output characteristics and frequency response of the sensors are investigated. The temperature stability is evaluated by measuring output power fluctuations of the sensors. Experiment results reveal that the sensitivity of the through type sensor is a little higher than that of the reflective type sensor, while the size (length) of the reflective type sensor is only half of the through type. Besides, as only a single optical fiber is coupled, it is convenient for the reflective type sensor to measure in very small space. Applications of the sensor for measurement of the lightning electromagnetic pulse, nuclear electromagnetic pulse, and pulsed radio frequency fields are demonstrated. The measurement results indicate that the developed integrated optics sensor has powerful potential and is expected to be widely used for measurement of intense pulsed electric fields.

High-efficiency synthesis of high-performance K0.5Na0.5NbO3 ceramics

Pure (K0.5Na0.5)NbO3 (KNN) ceramics with high density, fine and uniform-size grains were prepared by mechanochemical activation-assisted process. The time of synthesis is only 100 min, which is 72% – 93% shorter than the 6–24 h of the conventional solid-state method. Compared to samples prepared by conventional solid-state method, both the microstructure evolvement and electric properties were explored in detail. Results show the electric properties was significantly improved. Moreover, the dielectric and ferroelectric properties of obtained KNN ceramics exhibit strong dependence on the crystal size of the initial powders. The optimized ceramics HKNN100 showed a quite high energy storage performance, i.e., large electric energy storage density (Wtol = 1.612 J/cm3) and recoverable energy storage density (Wrec = 0.431 J/cm3), which can be mainly ascribed to the large dielectric breakdown strength (DBS = 110 kV/cm). Our works demonstrated that mechanochemical activation-assisted method possesses advantages for high-efficiency preparation of KNN or KNN-based ceramics.

Enhanced energy-storage performance of (1-x)(0.72Bi0.5Na0.5TiO3-0.28Bi0.2Sr0.7□0.1TiO3)-xLa ceramics

Leed-free ferroelectric (1-x)(0.72Bi0.5Na0.5TiO3-0.28Bi0.2Sr0.7□0.1TiO3)-xLa (NBST-xLa; x = 0, 0.5%, 1.5%, 2%) ceramics were synthesized using a conventional solid-state reaction method and the effect of La-doping on the microstructure and electrical properties was investigated. The introduction of La could reduce the grain size and improve the porosity of NBST ceramics. Temperature-dependent dielectric permittivity illustrated that the relaxation properties of NBST-xLa ceramics changed parabolically with the increase of La content. The introduction of La gave rise to a large dielectric breakdown strength and maximum polarization when x = 0.5%, which was attributed to the variation of the microstructure and the relaxation properties of NBST-xLa ceramics, respectively. The optimum effective energy storage density of 1.2 J/cm3 at 90 kV/cm was achieved when x = 0.5%. These results indicated that NBST-0.5%La ceramic may provide a practical perspective for energy storage ceramics research.

High energy-storage density of lead-free BiFeO3 doped Na0.5Bi0.5TiO3-BaTiO3 thin film capacitor with good temperature stability

In this work, the lead-free and BiFeO3 doping Na0.5Bi0.5TiO3-BaTiO3 thin films [(0.94-x)Na0.5Bi0.5TiO3-0.06BaTiO3-xBiFeO3 (NBT-6BT-xBFO), x = 0.00, 0.01, 0.03, 0.05 and 0.07] were deposited on Pt/Ti/SiO2/Si substrates by a sol-gel method. The enhanced ferroelectric properties and high energy-storage density have been achieved at 5% BiFeO3 substitution. Moreover, the 5% BiFeO3 doping Na0.5Bi0.5TiO3-BaTiO3 (0.89NBT-0.06BT-0.05BFO) thin-films exhibited a high dischargeable energy density (Wrecovered) of 42.9 J/cm3 with a corresponding energy-storage efficiency (η) of 65.7% under an electric field of 1720 kV/cm, and the high temperature stabilities with regard to their energy-storage properties over temperatures ranging from room temperature to 260 °C were demonstrated, and the charging and discharging characteristics demonstrate the faster microsecond discharge and large dielectric strength of the thin film capacitor. The results indicated that the 0.89NBT-0.06BT-0.05BFO thin-films might be promising environmentally friendly lead-free materials for energy-storage capacitor application.

Hierarchical micro-nanostructured albite-based glass-ceramic for high dielectric strength insulators

A novel glass-ceramic material based on albite type Na-rich feldspar has been synthesized by conventional ceramic process. High crystallinity, >94% Vol.% is obtained by fast sintering which allows energy saving processing. Albite is the main crystalline phase and tetragonal SiO2 is a secondary phase. Electrical properties were examined by complex impedance, DC measurements, and dielectric breakdown test. Dielectric characterization shows a non-Debye type dielectric behavior with low dielectric constant, 4.6 at 1 MHz, low dielectric losses, (∼10−3 at 1 MHz, and a large dielectric strength, ∼60 kV/mm), that it is the largest value reported in ceramic insulators. Those dielectric properties are attained by the low glassy phase content in the samples and their unique micro-nanostructure. All these properties make this novel material a very promising candidate in the market of ceramic electrical insulator, highlighting for high-voltage applications.