Electrical energy density and dielectric properties of poly(vinylidene fluoride-chlorotrifluoroethylene)/BaSrTiO3 nanocomposites

A series of poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE))/barium strontium titanate (BST) nanocomposites were fabricated by solution casting method. The addition of BST nanoparticles could enhance both the dielectric constant and the displacement of the resultant composite significantly. The surface activation of BST nonaparticles with KH550 was confirmed as an effective way to improve the breakdown strength of the composite. The high electric displacement (D > 15 μC/cm²), breakdown field (>200 MV/m) and low dielectric loss in P(VDF-CTFE)/BST nanocomposites suggest that the high electrical energy density may be desirable. That indicates the potential application of this class of copolymer/ceramics nanocomposites for high energy storage components.     

Improvement of dielectric breakdown strength and energy storage performance in Er2O3–modified 0.95Sr0.7Ba0.3Nb2O6-0.05CaTiO3 lead-free ceramics

In this study, 0.95?Sr_0.7Ba_0.3Nb₂O₆-0.05CaTiO₃-x wt% Er₂O₃ ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr_0.7Ba_0.3Nb₂O₆-0.05CaTiO₃ ceramics, the Er₂O₃ dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm³ and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors.     

Enhanced energy storage properties of BaO-K2O-Nb2O5-SiO2 glass ceramics obtained through microwave crystallization

BaO-K₂O-Nb₂O₅-SiO₂ (BKNS) glass ceramics were prepared by microwave crystallization of transparent glass matrices and the effects of microwave treatment temperature on their dielectric performances, phase structure, microstructure and breakdown strength (BDS) were investigated systematically. X-ray diffraction results suggested that microwave treatment had no significant influence on the type of precipitated phases. The microstructure of the glass ceramics was remarkably optimized via microwave treatment. The dielectric constant and breakdown strength of microwave-treated samples were significantly improved as compared with conventional-heated samples at the same temperature. The maximum theoretical energy storage density of microwave-treatment samples at 750?°C reached 12.7?J/cm³, which was larger than that of the conventional-heated samples (8.6?J/cm³).     

Dielectric relaxation behavior and energy storage properties in Ba0.4Sr0.6Zr0.15Ti0.85O3 ceramics with glass additives

Ba_0.4Sr_0.6Zr_0.15Ti_0.85O₃ ceramics with SrO–B₂O₃–SiO₂ glass additives were prepared via the solid state reaction route. The effects of glass contents on the sintering behavior, dielectric properties, microstructures, and energy storage properties of BSZT ceramics were investigated. Dielectric breakdown strength of 22.4 kV/mm was achieved for BSZT ceramics with 20 wt% glass addition. Dielectric relaxation behavior was observed in dielectric loss versus temperature plots. In order to investigate the mechanism of dielectric breakdown performance, the relationship between dielectric breakdown strength and grain boundary barrier was studied by the measurements of breakdown strength and activation energy. A discharged energy density of 0.45 J/cm³ with an energy efficiency of 88.2% was achieved for BSZT ceramics with 5 wt% glass addition.     

Ba0.4Sr0.6TiO3/MgO Composites with Enhanced Energy Storage Density and Low Dielectric Loss for Solid-State Pulse-Forming Line

(100−x) wt% Ba_0.4Sr_0.6TiO₃−x wt% MgO composites (10≤x≤30) were prepared using Ba_0.4Sr_0.6TiO₃ powder and nanosized MgO powder (∼60 nm) by a solid-state reaction. The energy storage density and dielectric loss were investigated for the purpose of a potential application in solid-state pulse-forming line. The results show that Ba_0.4Sr_0.6TiO₃/MgO composites exhibit a notably enhanced energy density and low dielectric loss, compared with pure Ba_0.4Sr_0.6TiO₃. The enhancement of the energy density is attributed to the notable increase in breakdown strength of the composites and the improvement of dielectric constant stability with regard to electric field. In the case of x=30, the samples exhibited a breakdown strength of 33.1 kV/mm, an energy density of 1.14 J/cm³, a moderate dielectric constant of 270, and a low dielectric loss of 4 × 10⁻⁴.     

MgO-modified Sr0.7Ba0.3Nb2O6 ceramics for energy storage applications

We explored the phase structure, microstructure, dielectric and energy storage properties of MgO-modified strontium barium niobate Sr_0.7Ba_0.3Nb₂O₆-xwt%MgO (SBNMx; x?=?0–5) ceramics fabricated via conventional solid-state sintering precess. X-ray diffraction analysis indicates Mg²⁺ incorporates into lattice at x?=?0.5 and secondary phases come into formation for samples at x?≥?1, which results in the decrease of dielectric constant. There is also significant reduction of dielectric loss up to 0.002. Compared with pure SBN ceramics, the grain size of SBNMx ceramics becomes denser and more uniform, moreover, the dielectric breakdown strength shows increasing trend from 137?kV/cm to 226?kV/cm, which is in favor of the energy storage. SBNM0.5 ceramics presents the optimal energy storage performance: energy storage density of 0.93?J/cm³ and energy storage efficiency of 89.4% at 157?kV/cm, indicating that SBNM ceramics are prospective candidates for high voltage capacitor applications.     

High energy density nanocomposites based on poly(vinylidene fluoride‐chlorotrifluoroethylene) and barium titanate

Three series of poly (vinylidene fluoride‐chlorotrifluoroethylene)/barium titanate (BT) nanocomposites with varied compositions were fabricated via solution cast process followed by thermally treated in different ways. Quenching the composite samples at lower temperature could effectively enhance their dielectric constant, breakdown strength as well as the energy density. The highest energy density (13.6 J/cm³) is observed in the sample quenched from 200°C to ?94°C with 5 vol% BT, which is much higher than nanocomposites reported in the current literature. The addition of ceramic particles leads to the improvement of dielectric permittivity and energy density measured under the same electric field. However, the dielectric breakdown strength and the energy density measured at breakdown strength of the resultant composites are reduced as a function of BT content. The fixed maximum electric displacement and reduction of saturation electric field suggest that the addition of ceramic particles with high dielectric constant may help increase the energy density of composites under low electric field but not for high electric field. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Nanocomposites of Surface‐Modified BaTiO3 Nanoparticles Filled Ferroelectric Polymer with Enhanced Energy Density

We report nanocomposites of increased dielectric permittivity, enhanced electric breakdown strength and high‐energy density based on surface‐modified BaTiO₃ (BT) nanoparticles filled poly(vinylidene fluoride) polymer. Polyvinylprrolidone (PVP) is used as the surface modification agent and homogeneous nanocomposite films have been prepared by solution casting processing. The dielectric permittivity of the nanocomposite with treated BT is higher than those with untreated BT and reaches the maximum value of 77 (1 kHz) at BT concentration of 55 vol%. The electric breakdown strength of the nanocomposite is greatly enhanced to 336 MV/m at BT concentration of 10 vol% and the calculated energy density is 6.8 J/cm³. The results indicate that using PVP as surface modification agent can greatly enhance the dielectric permittivity and electric breakdown strength of the ceramic–polymer nanocomposite and achieve high‐energy density for energy storage and power capacitor applications.     

Effects of TiO2 addition on dielectric and energy storage properties of BaO-K2O-Nb2O5-SiO2 glass ceramics

In this work, 25.6BaO-6.4K₂O-32Nb₂O₅-36SiO₂-xTiO₂ (0 ≤ x ≤10 mol%) (BKNST) glass ceramics were synthesized by conventional melts and controllable crystallization method. The effects of different TiO₂ addition on the phase composition, dielectric and energy storage properties of BKNS glass ceramics were systematically evaluated. With the TiO₂ concentration increasing, a growing content of Ba₂TiO₄ phase was observed in the glass ceramics. The microstructures appeared to be homogenous and uniform with very low porosity through the addition of TiO₂, for which the maximal breakdown strength of 2112 kV/cm and the corresponding energy storage density of 9.48 J/cm³ were obtained with x = 7.5. The extremely low dielectric loss of less than 1‰ (25 °C, 100 kHz) and the obviously improved microstructure contributed to the increased breakdown strength. In addition, the discharge power density of the glass-ceramic capacitor (x = 7.5) was investigated using the RLC charge-discharge circuit and a relatively high value of 16 MW/cm³ at 300 kV/cm was obtained.     

Enhanced dielectric properties of three phase dielectric MWCNTs/BaTiO3/PVDF nanocomposites for energy storage using fused deposition modeling 3D printing

This research studied the effect of fused deposition modeling (FDM) 3D printing on three phase dielectric nanocomposites using poly(vinylidene) fluoride (PVDF), BaTiO₃ (BT), and multiwall carbon nanotubes (CNTs). PVDF polymer and BT ceramics are piezo-, pyro- and di-electric materials extensively used for sensor and energy storage/harvesting applications due to their unique characteristic of dipole polarization. To increase dielectric property, CNTs have been recently utilized for uniform dispersion of BT nanoparticles, ultrahigh polarization density, and local micro-capacitor among matrix. It was proved that 3D printing process provides homogeneous dispersion of nanoparticles, alleviating agglomeration of nanoparticles and reducing micro-crack/voids in matrix which can potentially enhance their dielectric property than traditional methods. In this research, these three-phase nanocomposites are fabricated through FDM 3D printing process and characterized for dielectric property. Increasing both BT and CNT nanoparticles improves dielectric properties, while CNTs have a percolation threshold near 1.7?wt%. The most desirable combination of dielectric constant and loss properties (118 and 0.11 at 1?kHz) is achieved with nanocomposites containing 1.7?wt%-CNT/45?wt%-BT/PVDF. These results provide not only a technique to 3D print dielectric nanocomposites with improved dielectric property but also large-scale electronic device manufacturing possibility with freedom of design, low cost, and faster process.     

Eco-friendly poly(vinyl alcohol)/delaminated V2C MXene high-k nanocomposites with low dielectric loss enabled by moderate polarization and charge density at the interface

High-dielectric-constant (high-k) polymer/conductor composites with low dielectric loss are desirable for energy storage. However, high leakage currents from interfacial regions with high charge density are difficult to handle. In this work, high permittivity and low dielectric loss were achieved in poly(vinyl alcohol) (PVA)/V₂C MXene nanocomposite films fabricated by solution casting by taking advantage of the interfacial compatibility and moderate interfacial charge density of the nanocomposites. Water-soluble PVA was utilized as the polymer matrix. Delaminated V₂C MXene nanosheets with appropriate conductivity were prepared and used as the filler. The mild interface polarization of the nanocomposites was responsible for achieving favourable permittivity values. The small gap between the work functions of PVA and V₂C contributed to moderate interfacial charge density values and thus low dielectric loss values. A proportional correlation between the interfacial charge density and the conductivity of composites was also verified. The depth of charge injection from the MXene to PVA was found to be half of the interlamellar spacing of the delaminated MXene. The dependence of the electrical properties of the nanocomposites on the frequency and MXene content was also studied. The composite with 4 wt% MXene exhibited a permittivity of ~24 (16 times that of PVA) and a dielectric loss of ~0.14 (1.5 times that of PVA) at 1 kHz, as well as breakdown strength of ~31 MV m⁻¹ (63% of PVA). This work might enable environmentally friendly fabrication of promising composite dielectrics.     

Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr_0.2Ti_0.8)O₃-(1-x)(Ba_0.7Ca_0.3)TiO₃ [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (T_R-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (T_T-C) of 110?°C. The dielectric analysis suggests that the phase transition at T_T-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A₁, E(LO) Raman mode. The saturation polarization (P_s) ≈8.3?μC/cm² and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 10⁵ cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high T_T-C (110?°C), a high dielectric constant (ε_r ≈?12,285) with low dielectric loss (0.03), good polarization (P_s ≈?8.3?μC/cm²) and large recoverable energy density (W?=?121?mJ/cm³) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.     

Enhanced energy-storage properties of (1-x)(0.7Bi0.5Na0.5TiO3-0.3Bi0.2Sr0.7TiO3)-xNaNbO3 lead-free ceramics

A series of (1-x)(0.7Bi_0.5Na_0.5TiO₃-0.3Bi_0.2Sr_0.7TiO₃)-xNaNbO₃ (BNT-BST-100xNN) lead-free ceramics were fabricated using conventional solid-state reaction technique. The phase behavior, microstructure, dielectric, ac impedance and energy-storage properties of the sintered ceramics were systematically investigated. XRD patterns and surface SEM micrographs revealed the introduction of NaNbO₃ didn't change the perovskite structure of BNT-BST at low doping level. The NaNbO₃ doping gave rise to slimmer P-E loops and thus gained enhanced energy storage properties. Therefore, a maximum energy storage density of 1.03 J/cm³ was achieved at 85 kV/cm at x = 0.01 via increasing the dielectric breakdown strength (DBS). Temperature-dependent dielectric permittivity illustrated the enhanced relaxor characteristics, implying the long-rang ferroelectric order was further damaged due to the introduction of NaNbO₃. The results above indicate the sintered ternary ceramics can be a promising lead-free candidate for energy storage capacitors.     

Self-growth of nanocrystalline structures for amorphous Sr0.925Bi0.05TiO3 thin films with high energy density

Process of self-growth nanocrystalline structure was explored to improve the dielectric properties of amorphous Sr_0.925Bi_0.05TiO₃ (SBT) thin films through controlling the annealing temperature. The crystallinity of the material was 15% when annealed at 550?°C, and the resulting nanocrystalline particles were 14?nm in size as determined by XRD analysis. Therefore, the proposed process could produce a novel film of an amorphous matrix coating nanocrystalline particles. Finite element analysis results showed that the applied electric field was focused primarily in the amorphous matrix, which could effectively decrease the probability of low voltage breakdown of the nanocrystalline particles. Simultaneously, the nanocrystalline particles supplied more polarization charges, which helped to improve the dielectric constant of the inorganic composite. Combining the merits of amorphous and crystalline phases, the ultimate energy storage density of the modified sample was as high as 21.2?J/cm³, which represents an improvement of 5.1?J/cm³ compared with that of pure amorphous SBT thin film.     

High permittivity nanocomposites fabricated from electrospun polyimide/BaTiO3 hybrid nanofibers

High dielectric permittivity, good mechanical properties, and excellent thermal stability are highly desired for the dielectric materials used in the embedded capacitors and energy‐storage devices. This study reports polyimide (PI)/barium titanate (BaTiO₃) nanocomposites fabricated from electrospun PI/BaTiO₃ hybrid nanofibers. The PI/BaTiO₃ nanocomposites were investigated using Fourier transform infrared spectroscopy, scanning electron microscope, transmission electron microscope, thermal gravimetric analysis, an electromechanical testing machine, a LCR meter and an electric breakdown strength tester. The results showed that BaTiO₃ fillers were uniformly dispersed up to 50 vol% in PI matrix. The dielectric permittivity of the composite (50 vol% BaTiO₃) was 29.66 with a dielectric loss of 0.009 at 1 kHz and room temperature. The dielectric permittivity showed a very small dependence on temperature (up to 150°C) and frequency (100 Hz–100 kHz). The nanocomposites also showed high thermal stability and good mechanical properties. The PI/BaTiO₃ nanocomposites will be a promising candidate for uses in embedded capacitors, especially in high temperature circumstance. POLYM. COMPOS., 37:794–801, 2016. © 2014 Society of Plastics Engineers     

Effect of sintering temperature and Ho2O3 on the properties of TiO2-based varistors

In this study, a series of TiO₂-based ceramics doped with different contents of Ho₂O₃ in the range of 0–0.6?mol% are prepared by means of a conventional solid-state reaction method. Phase composition, microstructure and element distribution are studied by use of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) separately. The influence of sintering temperature and Ho₂O₃ on the properties of samples is explored. The results show that the breakdown voltage decreases continuously while both the nonlinear coefficient and the relative dielectric constant ascend firstly and then descend with the sintering temperature increasing. Meanwhile, the relative dielectric constant and nonlinear coefficient of samples firstly ascend and then descend with the increasing of Ho₂O₃. Although the minimum breakdown voltage (3.3?V/mm) is obtained when sample is sintered at 1450?°C, the sample doped with 0.45?mol% Ho₂O₃ sintered at 1400?°C exhibits high comprehensive electrical properties, with breakdown voltage of 6?V/mm, the nonlinear coefficient of 5.5 and the relative dielectric constant of 1.88?×?10⁵.     

Highly-efficient electromagnetic interference shielding and microwave dielectric behavior of a (Bi2O3 + B2O3)-doped MWCNT/BaTiO3 ceramic nanocomposite

Microwave dielectric properties along with electromagnetic interference shielding effectiveness (EMI SE) of a multi-walled carbon nanotube (MWCNT)/barium titanate (BaTiO₃) nanocomposite are investigated in this paper. Appropriate amount of sintering additive (Bi₂O₃ +?B₂O₃) was doped into some nanocomposites to reduce the sintering temperatures. The dielectric properties of the nanocomposites with various MWCNT and sintering additive contents were evaluated at different microwave frequency ranges. It was found that the incorporation of optimized amount of (Bi₂O₃ +?B₂O₃) can give rise to significantly good dielectric properties. Results also indicated that incorporation of 6?wt% (Bi₂O₃ +?B₂O₃) into 1.5?mm-thick nanocomposite containing 8?wt% MWCNT led to an EMI SE greater than 28?dB, suggesting this novel nanocomposite as a promising candidate for microwave absorption and electromagnetic interference applications.     

Large-scale and ultra-low thermal conductivity of ZrO2 fibrofelt/ZrO2-SiO2 aerogels composites for thermal insulation

The large-scale fibrous/aerogels composites are prepared by using zirconia fibrofelt (ZFF) as skeleton to give high strength and ZrO₂-SiO₂ aerogels (ZSA) as filler to give excellent thermal insulation through vacuum impregnation. The ZFF/ZSA with a low density of 0.302?g/cm³ and a high porosity (89%) exhibits large size of 180?mm in length, 180?mm in width and 25?mm in height which is larger than other fibrous aerogels. Meanwhile, the ZFF/ZSA exhibits high compressive strength of up to 0.17?MPa which is approximately six times higher than that of ZFF (0.028?MPa). The ZFF/ZSA shows a much lower thermal conductivity of 0.0341?W?m^?1 K^?1 at room temperature and 0.0460–0.096?m^?1 K^?1 during 500?°C and 1100?°C which are lower than that of conventional fibrous materials, indicating its excellent thermal insulation property in a wide temperature range, and the thermal insulation mechanism is analyzed. Thus, the large-scale, low density, high strength, and low thermal conductivity of ZFF/ZSA composites show enormous potential application in the fields of architecture, engineering pipes and aerospace for thermal insulation and protection.     

Bi0.5Na0.5TiO3-BaTiO3-CaZrO3:ZnO high-temperature dielectric composites with wide operational range

0.82[0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃]-0.18CaZrO₃:xZnO (BNT-BT-CZ:xZnO, x = 0–0.40 with interval of 0.10) high temperature dielectric composites were prepared and the structural and electrical properties were investigated. Significantly improved temperature-insensitive permittivity spectra have been observed in the composites: the temperature range for low variance in permittivity (Δε_r/ε_r,150?°C < 10%) is 70–190?°C for x?=?0, whereas it is extended at least to 30–250?°C for the optimal x?=?0.10 at 1?kHz. Especially, for this optimal composite, the variance of permittivity is less than 4.0% in the temperature range of 30–400?°C with the suitable permittivity value of ~ 600 at 10?kHz. By comparatively investigating the properties of unpoled and poled samples, the improved temperature-insensitive permittivity is rationalized by the ZnO-induced local electric field that can suppress the evolution of polar nanoregions and thus enhance the temperature-insensitivity of permittivity.     

Energy storage density and tunable dielectric properties of BaTi0.85Sn0.15O3/MgO composite ceramics prepared by SPS

(100-x) wt.% BaTi_0.85Sn_0.15O₃–x wt.% MgO (BTS/MgO) composite ceramics were prepared by spark plasma sintering (SPS) technology. Phase constitution, microstructure, dielectric and electrical energy storage properties of BTS/MgO composite ceramics were investigated. The samples prepared by SPS had smaller grain size and presented layer-plate substructure. Dielectric permittivity and dielectric loss of BTS/MgO composite ceramics decreased significantly with the content of MgO increasing, and dielectric tunability maintained a relatively high value (>45%). Meanwhile, the dielectric breakdown strength was improved when addition of MgO in BTS matrix, which resulted in a significant improvement of energy storage density. The high dielectric breakdown strength of 190 kV/cm, energy storage density of 0.5107 J/cm³ and energy storage efficiency of 92.11% were obtained in 90 wt.% BaTi_0.85Sn_0.15O₃–10 wt.% MgO composite ceramics. Therefore, BTS/MgO composites with good tunable dielectric properties and electrical energy storage properties could be exploited for energy storage and phase shifter device applications.