Silicone rubbers for dielectric elastomers with improved dielectric and mechanical properties as a result of substituting silica with titanium dioxide

One prominent method of modifying the properties of dielectric elastomers (DEs) is by adding suitable metal oxide fillers. However, almost all commercially available silicone elastomers are already heavily filled with silica to reinforce the otherwise rather weak silicone network and the resulting metal oxide filled elastomer may contain too much filler. We therefore explore the replacement of silica with titanium dioxide to ensure a relatively low concentration of filler. Liquid silicone rubber (LSR) has relatively low viscosity, which is favorable for loading inorganic fillers. In the present study, four commercial LSRs with varying loadings of silica and one benchmark room-temperature vulcanizable rubber (RTV) were investigated. The resulting elastomers were evaluated with respect to their dielectric permittivity, tear and tensile strengths, electrical breakdown, thermal stability and dynamic viscosity. Filled silicone elastomers with high loadings of nano-sized titanium dioxide (TiO₂) particles were also studied. The best overall performing formulation had 35 wt.% TiO₂ nanoparticles in the POWERSIL® XLR LSR, where the excellent ensemble of relative dielectric permittivity of 4.9 at 0.1 Hz, breakdown strength of 160 V µm^?1, tear strength of 5.3 MPa, elongation at break of 190%, a Young’s modulus of 0.85 MPa and a 10% strain response (simple tension) in a 50 V μm^?1 electric field was obtained.     

Octakis(phenyl)-T8-silsesquioxane-filled silicone elastomers with enhanced electromechanical capability

The first dielectric elastomer actuators based on electroactive nanocomposites with octakis(phenyl)-T8-silsesquioxane (phenyl-T8), obtained ex-situ, used as voltage stabilizer filler for silicone elastomers are reported. The incorporation and homogeneous dispersion of crystalline phenyl-T8 in percentages of 2.5, 3.5, 5, and 10 into the amorphous matrix consisting in a polydimethylsiloxane-α,ω-diol with Mn = 240,000 g/mol was successfully achieved by solution mixing and crosslinking. For the sample with the best actuation performance (that containing 3.5 wt.% filler), an optimized filled elastomer was obtained by dispersing 3.6 wt. % phenyl-T8 in the matrix using a suitable surfactant (Pluronic L81), thus gaining an increased electrical breakdown of 30% compared with the pristine sample. Beside dielectric strength, the matured films were characterized in terms of morphology, mechanical, dielectric and actuation tests. In spite of structural incompatibility between the filler and the matrix, the obtained materials are soft elastomers showing high strain (~800%) and low Young's modulus of 50–100 kPa. The use of phenyl-T8 in a silicone matrix lead to electroactive films with slightly increased lateral actuation strain and electric breakdown strength.     

Electrical breakdown of an acrylic dielectric elastomer: effects of hemispherical probing electrode’s size and force

Dielectric elastomers are widely investigated as soft electromechanically active polymers (EAPs) for actuators, stretch/force sensors, and mechanical energy harvesters to generate electricity. Although the performance of such devices is limited by the dielectric strength of the constitutive material, the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied. Here, we describe a custom-made setup to measure electrical breakdown of soft EAPs, and we present data for a widely studied acrylic elastomer (VHB 4905 from 3M). The elastomer was electrically stimulated via a planar and a hemispherical metal electrode. The breakdown was characterized under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode. With a given radius of curvature, the breakdown field increased by about 50% for a nearly 10-fold increase of the applied mechanical stress, while with a given mechanical stress the breakdown field increased by about 20% for an approximately twofold increase of the radius of curvature. These results indicate that the breakdown field is highly dependent on the boundary conditions, suggesting the need for reporting breakdown data always in close association with the measurement conditions. These findings might help future investigations in elucidating the ultimate breakdown mechanism/s of soft elastomers.     

Electro-Thermal model of thermal breakdown in multilayered dielectric elastomers

Energy transduction of dielectric elastomers involves minute electrical and mechanical losses, both of which potentially increase the temperature within the elastomer. Thermal breakdown of dielectric elastomers occur when heat generated therein cannot be balanced by heat loss on the surface, which is more likely to occur in stacked dielectric elastomers. In this article an electro-thermal model of a multilayered dielectric elastomer able to predict the possible number of layers in a stack before thermal breakdown occurs is presented. Simulation results show that point of breakdown is greatly affected by an increase in surrounding temperature and applied electric field. Furthermore, if the stack diameter is large, thermal insulation of the cylindrical surface is a valid approximation. Two different expressions for the electrical conductivity are used, and it is concluded that the Frank-Kamenetskii expression is more conservative in prediction of point of breakdown than the Arrhenius expression, except at high surrounding temperature. © 2018 American Institute of Chemical Engineers AIChE J, 65: 859–864, 2019     

Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites

Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation.

     

Silicone elastomers with high dielectric permittivity and high dielectric breakdown strength based on dipolar copolymers

Dielectric elastomers (DEs) are a promising new transducer technology, but high driving voltages limit their current commercial potential. One method used to lower driving voltage is to increase dielectric permittivity of the elastomer. A novel silicone elastomer system with high dielectric permittivity was prepared through the synthesis of siloxane copolymers, thereby allowing for the attachment of high dielectric permittivity molecules through copper-catalysed azide-alkyne 1,3-dipolar cycloaddition (CuAAC). The copolymers have a high degree of chemical freedom, as the dimethylsiloxane spacer units between the functional groups, as well as the degree of functionalisation, can be varied. Thus, the best overall properties were obtained for an elastomer prepared with a copolymer with a 1200 g mol⁻¹ dimethylsiloxane spacer unit and 5.6 wt% of the high dielectric permittivity molecule 1-ethynyl-4-nitrobenzene. Here, a high increase in dielectric permittivity (∼70%) was obtained without compromising other favourable DE properties such as elastic modulus, gel fraction, dielectric loss and electrical breakdown strength.     

Enhanced Electromechanical Properties of Three-Phased Polydimethylsiloxane Nanocomposites via Surface Encapsulation of Barium Titanate and Multiwalled Carbon Nanotube with Polydopamine

Owing to its low modulus, high breakdown strength, and low dielectric loss, polydimethylsiloxane (PDMS) is used as a great dielectric elastomer despite its low dielectric permittivity. Herein, polydopamine (PDA) is used to encapsulate barium titanate (BT) and multiwalled carbon nanotube (MWCNT) in situ during its polymerization to prepare core–shell structured fillers, which are then solution-compounded with PDMS, and subsequently vulcanized with a cross-linking agent. The resulting three-phased nanocomposites exhibit improved filler-PDMS interactions upon filler PDA-encapsulation likely due to interfacial hydrogen bonding, thereby to enhance filler dispersion within the PDMS matrix. Compared with the unencapsulated PDMS nanocomposites, a softening effect (i.e., decreased cross-linking) by the finer filler-dispersion, in the context of a hardening effect by filler network formation, strengthens in the PDA-modified nanocomposites to produce their lower moduli. Additionally, the insulating, interfacial PDA partially inhibits the formation of conductive paths and leakage currents, causing decreased dielectric loss while increased breakdown strength of the nanocomposites. Therefore, the PDA-encapsulated BT and MWCNT filled PDMS nanocomposites display excellent electromechanical properties with a largest possible actuated strain of 7.0% at a breakdown strength of 13.9 kV mm⁻¹, which is 1.8 times that (3.9%@15.0 kV mm⁻¹) of their unencapsulated counterparts and 4.7 times that (1.5%@18.4 kV mm⁻¹) of unfilled, neat PDMS.     

Electro-thermal and -mechanical model of thermal breakdown in multilayered dielectric elastomers

Multiple breakdown phenomena may take place when operating dielectric elastomers. Thermal breakdown, which occurs due to Joule heating, becomes of special importance when using multilayered stacks of dielectric elastomers, due to the large volume-to-surface-area-ratio. In this article, a 2D axisymmetric finite-element model of a multilayered stack of dielectric elastomers is set up in COMSOL Multiphysics®. Both the electro-thermal and electro-mechanical couplings are considered, allowing for determination of the onset of thermal breakdown. Simulation results show that an entrapped particle in the dielectric elastomer drastically reduces the possible number of layers in the stack. Furthermore, the possible number of layers is greatly affected by the ambient temperature and the applied voltage. The performance of three hyperelastic material models for modeling the elastomer deformation are compared, and it is established that the Gent model yields the most restrictive prediction of breakdown point, while the Ogden model yields the least restrictive estimation.     

Importance of Mullins effect in commercial silicone elastomer formulations for soft robotics

Silicone elastomers are used in a wide range of applications, including artificial muscles, biomedical devices, and soft robotics, for which chemical, thermal, and mechanical stability are important requirements that these elastomers must fulfill. However, to ensure that silicone elastomers' properties and performance remain constant under long-term deployment, it is necessary to examine and account for the Mullins effect, which has the potential to significantly alter certain elastomer properties of interest. In this article, the mechanical properties of soft and hard commercial silicone elastomers and two blends of commercial silicone elastomers are investigated—specifically their softening behavior due to the Mullins effect. Ultimate stresses, ultimate strains, and Young's moduli are obtained from uniaxial tensile tests. Results show that the point of softening greatly depends on both the elastomer type and its strain history. Furthermore, a significant permanent set is observed in the softest commercial formulations.     

Anomalous behavior of the dielectric and electrical properties of polymeric nanodielectric poly(vinyl alcohol)–titanium dioxide films

The complex dielectric permittivity, alternating‐current electrical conductivity, electric modulus, and impedance spectra of polymeric nanocomposite (PNC) films consisting of a poly(vinyl alcohol) (PVA) matrix dispersed with nanosize particles of titanium dioxide (TiO₂); (i.e., PVA–x wt % TiO₂, where x is 0, 1, 3, or 5) were investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. A detailed analysis of the results showed that the values of the dielectric and electrical parameters of these PNC‐based nanodielectric films varied anomalously with increasing TiO₂ concentration. The temperature‐dependent dielectric characterization of the PVA–3 wt % TiO₂ film revealed that the dielectric polarization at a fixed frequency increased nonlinearly with increasing temperature. The temperature‐dependent electric modulus relaxation time values of the nanodielectric film obeyed Arrhenius behavior. The X‐ray diffraction study confirmed that the crystalline phase of the PVA matrix decreased with increasing TiO₂ concentration; this suggested that the interaction of the TiO₂ nanoparticles caused some destruction of the hydroxyl group dipolar ordering in the hydrogen‐bonded crystalline structure of the pristine PVA matrix. The intensities of the diffraction peaks of the TiO₂ nanofiller were enhanced as its concentration increased in these nanodielectrics; this confirmed the existence of TiO₂ nanoparticles inside the crystalline phases of the PVA matrix. The surface morphology of the films was examined by the study of their scanning electron micrographs. The feasibility of using these flexible polymeric nanodielectric films as electrical insulators and dielectric substrates in low‐power microelectronic devices operated at audio‐ and radio‐frequency electric fields was explored. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44568.     

Evaluation of PP/EPDM nanocomposites filled with SiO2, TiO2 and ZnO nanofillers as thermoplastic elastomeric insulators

Abstract

Thermoplastic elastomer, which has important characteristics for cable insulation, was developed by melt blending of polypropylene (PP) with ethylene propylene diene monomer (EPDM) at various blend ratios together with SiO₂, TiO₂ and ZnO nanofillers at fixed loading of 2 vol.-%. The influence of EPDM content and the presence of nanofillers in the blend on burning rate, hydrophobicity and dielectric breakdown strength were investigated. Burning rate of PP/EPDM/ZnO was significantly reduced, implying that there was an improvement in fire retardancy with the addition of ZnO nanofillers in the polymer blend. Both SiO₂ and ZnO filled system showed an improvement in hydrophobicity. Furthermore, dielectric breakdown strength showed higher value in EPDM rich blends. In addition, the presence of nanofillers deteriorated the dielectric breakdown strength of PP/EPDM nanocomposites.     

Morphology,mechanical, and dielectric breakdown properties of PBT/PET/TPE,PBT/PET/PA66, PBT/PET/LMPE,and PBT/PET/TiO2 blends

The morphology and thermal behavior of tertiary blends of poly(butylene terephthalate) [PBT]/poly(ethylene terephthalate) [PET] alloy resin (Alloy)/thermoplastic elastomer (TPE), Alloy/nylon 66 (PA66), Alloy/low molecular weight polyester (LMPE), and Alloy/titanium dioxide (TiO₂) have been investigated by scanning electron microscopy, differential scanning calorimetry, and thermogravimetry (TG). In case of TPE and LMPE containing blends did not show any morphological change compared with Alloy whereas for PA66 containing blends, the size of the dispersed phase increased with the increase the PA66 contents. The crystallization peak of Alloy/TPE blends became undetectable with an increasing TPE content. In contrast, the crystallization temperature (T_c1) of Alloy/PA66, Alloy/LMPE, Alloy/TiO₂ blends increased significantly as the PA66, LMPE, and TiO₂ content increases. TG traces show a significant shift of the weight loss towards higher temperature for Alloy/TiO₂ blend whereas Alloy/TPE, Alloy/PA66 and Alloy/LMPE blends slightly decreases in thermal stability than Alloy. To investigate the applicability for insulation material, the prepared blend samples were extruded an electric wire and the breakdown voltage (BDV) of wires was investigated. The melt flow rate of Alloy increased as the amount of TPE increased, and a contrary trend was found when the increase of the amount of TiO₂. The dielectric breakdown test applies a voltage that is greater than the product's rated operating voltage for a specific period of time during which dielectric breakdown must not occur. The BDV of Alloy/TPE and Alloy/PA66 blends is higher than other blends before and after thermal aging 225°C for 30 min. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Preparation,morphology, and mechanical properties of elastomers based on polydimethylsiloxane/ polystyrene blends

Polydimethylsiloxane/polystyrene (PDMS/PS) blends were prepared by radical copolymerization of styrene (St) and divinylbenzene (DVB) in the presence of α,ω‐dihydroxy‐polydimethylsiloxane (PDMS), using benzoyl peroxide as initiator. The PDMS/PS blends obtained by this method are a series of stable, white gums, when the feed ratio of PDMS to St is 60/40 and DVB to St is not more than 2.0 wt %. Elastomers based on PDMS/PS blends were formed by crosslinking PDMS with methyl‐triethoxysilicane (MTES). The MTES dosage was much larger than the amount necessary for end‐linking hydroxy‐terminated chains of PDMS, with the excess being hydrolyzed to crosslinked networks, which were similar to SiO₂ and acted as filler. Mechanical property measurements show that the elastomers thus formed exhibit superior mechanical properties with respect to pure PDMS elastomer and the elastomers based on PDMS/PS system we prepared before. Moreover, investigations were carried out on the elastomers by extraction measurement and scanning electron microscopy (SEM). The extraction data show that the sol‐fraction decreases with increasing the feed ratio of DVB to St. SEM observation demonstrates that the elastomer has a microphase‐separated structure consisting of dispersed PS domains within a continuous PDMS matrix, and the extracted material exhibits a porous structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Maximum actuation strain for dissipative dielectric elastomers with simultaneous effect of prestretch and temperature

A dielectric elastomer can generate giant deformation by the voltage actuation, but the deformation is often hindered by the electromechanical instability and “snap‐through deformation,” which may lead to electrical breakdown. In this study, for the first time, the mathematical model is established for dissipative dielectric elastomers in the dynamic model with simultaneous effect of prestretch and temperature in order to achieve maximum actuation strain. The deformation of the dissipative dielectric elastomer: VHB 4905/4910 is investigated for the two simple actuation methods: constant and ramping voltage actuation, respectively. The best combined conditions of voltage and prestretch to obtain a large deformation at different operating temperatures are studied in detail. Under the best combined conditions, the influences of three factors: voltage, prestretch, and temperature on the maximum actuation strain are analyzed. This study should offer a great help in the design of dielectric elastomer actuators, and give the guidance to the accomplishment of the large deformation of dissipative dielectric elastomer actuators. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45850.     

Bilaterally Microstructured Thin Polydimethylsiloxane Film Production

Thin PDMS films with complex microstructures are used in the manufacturing of dielectric electro active polymer (DEAP) actuators, sensors and generators, to protect the metal electrode from large strains and to assure controlled actuation. The current manufacturing process at Danfoss Polypower A/S produces films with a one-sided microstructured surface only. It would be advantageous to produce a film with both surfaces microstructured, as this increases the film’s performance efficiency. The new technique introduced herein produces bilaterally microstructured film by combining an embossing method with the existing manufacturing process. In employing the new technique, films with microstructures on both surfaces are successfully made with two different liquid silicone rubber (LSR) formulations: 1) pure XLR630 and 2) XLR630 with titanium dioxide (TiO₂). The LSR films (～70 µm) are cast on a carrier web substrate using a coating blade. The carrier web, which has a sinusoidal corrugation with wave height of 7 µm and a wave period of 7 µm on its surface, imparts corrugations to the bottom surface of the film. The elastomer film on the carrier web is preheated to the gel point, where the elastomer film can retain an imprint made on it. The preheated film at gel point is embossed between the rolls of a gravure lab coater, which corrugates the top surface of the film. The films are then heated, in order to cure completely. For the LSR systems used in this process, the optimum conditions for preheating are 110°C for 4–7 s, while for embossing the temperature is 110°C with 25 psi pressure between the rolls at a speed of 1.4 rpm. Scanning electron microscope (SEM) images confirm the formation of microstructures on both the surfaces of the film.     

Conducting fluorine doped tin dioxide (FTO) coatings by ultrasonic spray pyrolysis for heating applications

Fluorine doped tin dioxide (FTO) coatings were deposited on AISI 304 stainless steel (SS) substrates using ultrasonic spray pyrolysis (USP) technique. Four different candidate insulating intermediate layers of TiO₂, MgO, Al₂O₃ and SiO₂ were selected and coated on AISI 304 SS using USP and investigated in order to overcome dielectric breakdown of FTO layer due to conductive nature of stainless steel substrate under the applied voltage. After the optimization of the process parameters for the depositions, only TiO₂ layer was successfully deposited while other oxides did not form continuous films on AISI-304 SS surface despite the efforts. SEM analysis, supported by back-scatter imaging, revealed thickness values of the layers for FTO and TiO₂, individually. Heating performances of the samples with varying sheet resistance values were examined under different applied voltages. Heating experiments showed that 300 °C can be reached with 10 V of applied voltage without occurrence of an electrical breakdown of FTO coating having 160 nm thickness with TiO₂ intermediate layer of 660 nm. 28.6% efficiency for the conversion of electrical energy into heat was calculated for FTO coating while bare stainless steel showed only 7.3% efficiency. Later, the heating experiments were repetitively conducted and the samples were tested under high relative humid environment to determine their resistance against moist conditions.     

Electric‐field response behaviors of chitosan/barium titanate composite hydrogel elastomers

Chitosan/barium titanate (BaTiO₃) composite hydrogel elastomers were prepared in the presence or absence of an applied direct‐current (dc) electric field. Scanning electron microscopy was used to observe the microstructure of the elastomers and the dispersion of particles in it. Tests of the storage moduli (Gs) of the elastomers were investigated with a dynamic mechanical analyzer. On this basis, the G increment and increment sensitivity were explored. The results show that the particles were sequentially dispersed, and the values of the G values for the elastomer were higher under an external applied dc electric field; this indicated that the composite elastomers exhibited excellent electric field response. Furthermore, the electric‐field response of the composite elastomers changed with the particle concentration, and the maximum response occurred when the mass fraction of BaTiO₃ was 2.0%. The G value of the composite elastomer with a BaTiO₃ weight percentage of 2.0 increased with increasing electric field; this revealed that the composite elastomer had a positive electric field response. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42094.     

Simultaneously improved actuated performance and mechanical strength of silicone elastomer by reduced graphene oxide encapsulated silicon dioxide

Herein, graphene oxide (GO)-encapsulated silica (SiO₂) hybrids (GO@SiO₂) were prepared via electrostatic self-assembly of the 3-aminopropyltriethoxysilane (APS)-modified SiO₂ and GO. The as-prepared GO@SiO₂ was introduced into polydimethylsiloxane (PDMS) elastomer to simultaneously increase the dielectric constant (k) and mechanical properties of PDMS. Then, the in situ thermal reduction of GO@SiO₂/PDMS composites was conducted at 180°C for 2 h to increase the interfacial polarizability of GO@SiO₂. As a result, the values of k at 1000 Hz are largely improved from 3.2 for PDMS to 13.3 for the reduced GO@SiO₂ (RGO@SiO₂)/PDMS elastomer. Meanwhile, the dielectric loss of the composites remains low (<0.2 at 1000 Hz). More importantly, the actuated strain at low electric field (5 kV/mm) obviously increases from 0.3% for pure PDMS to 2.59% for the composites with 60 phr of RGO@SiO₂, an eightfold increase in the actuated strain. In addition, both the tensile strength and elastic modulus are obviously improved by adding 60 phr of RGO@SiO₂, indicating a good reinforcing effect of RGO@SiO₂ on PDMS. Our goal is to develop a simple and effective way to improve the actuated performance and mechanical strength of the PDMS dielectric elastomer for its wider application.     

Enhanced dielectric constant and suppressed electrical conductivity in polymer nanocomposite films via loading MXene/TiO2/MoS2 nanosheets

Conductor/polymer nanocomposites can achieve high dielectric constant with low filler loading, but conductive fillers come into contact with each other easily, resulting in the formation of conductive paths. In this work, MXene/TiO₂/MoS₂ nanosheets were prepared by one-step hydrothermal method, and MXene/TiO₂/MoS₂/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposite films were prepared by solution casting method. At 1 kHz, with an optimized MXene/TiO₂/MoS₂ nanosheets loading of 8.0 wt%, MXene/TiO₂/MoS₂/P(VDF-HFP) nanocomposite films achieve a high dielectric constant of 944 and maintain a low dielectric loss of 0.19. TiO₂ and MoS₂ semiconductive layers on the surface of MXene nanosheets can prevent the formation of conductive paths, and therefore, nanocomposite films possess suppressed electrical conductivity. Moreover, MXene/TiO₂/MoS₂ nanosheets can build more microcapacitor structures in nanocomposite films with higher filler loading, which further improves the dielectric constant of nanocomposite films. Finite element simulation shows that TiO₂ and MoS₂ semiconductive layers can lower the electric field intensity and polarization intensity at the interface between conductive fillers and polymer matrix. Herein, MXene/TiO₂/MoS₂/P(VDF-HFP) nanocomposite films possess not only excellent dielectric properties, but also excellent mechanical properties, which can be used as flexible dielectric materials in electronic packaging technology.     

Effects of phase constitution and microstructure on energy storage properties of barium strontium titanate ceramics

Barium strontium titanate (Ba_0.3Sr_0.7TiO₃, BST) ceramics have been prepared by conventional sintering (CS) and spark plasma sintering (SPS). The effects of phase constitution and microstructure on dielectric properties, electrical breakdown process and energy storage properties of the BST ceramics were investigated. The X-ray diffraction analysis and dielectric properties measurements showed that the cubic and tetragonal phase coexisted in the SPS sample while the CS sample contained only tetragonal phase. Much smaller grain size, lower porosity, fewer defects and dislocation were observed in SPS samples, which greatly improved the electrical breakdown strength of the Ba_0.3Sr_0.7TiO₃ ceramics. The enhanced breakdown strength of the SPS samples resulted in an improved maximum electrical energy storage density of 1.13 J/cm³ which was twice as large as that of the CS sample (0.57 J/cm³). Meanwhile, the energy storage efficiency was improved from 69.3% to 86.8% by using spark plasma sintering.