Flexible and low cost lead free composites with high dielectric constant

Highly flexible lead free composite film having random distribution of ceramic filler was synthesized using Barium Titanate (BT) as a filler and inexpensive Thermoplastic Polyurethane (TPU) as a matrix. The results show that the 30 vol% BT-TPU composite has a dielectric constant of ~31 which is comparable to the expensive and difficult to produce PVDF based composites. With a breakdown field of 150 kV/mm, an energy density value of ~3 J/cm³ was estimated. These lead-free TPU based composites provide an alternative to PVDF based composites for energy storage applications.     

Ultrathin ceramic nanowires for high interface interaction and energy density in PVDF nanocomposites

Dielectric nanocomposites with ceramic fillers have a crucial role in energy storage applications. Therefore, poly(vinylidene fluoride) (PVDF) based nanocomposites filled with 20 nm diameter, surface hydroxylated BaTiO₃ nanowires (BTnws) were produced by solution-casting method in this work, in which BTnws were synthesized via solvothermal method. The dielectric constant of BTnws/PVDF nanocomposites was 24 when the content of fillers was 10vol% at 100 Hz and the breakdown strength could increase up to 417 kV/mm before decreasing. The nanocomposites showed enhanced energy density performance and the maximum energy density could reach to 8.1J/cm³ at 320 kV/mm with 10vol% BTnws, nearly tripled that of pure PVDF at 300 kV/mm. Finite element and molecular dynamic simulation results revealed that thin BTnws could create dielectric homogeneity in the nanocomposites and have strong interface interaction with PVDF molecular. The ultrathin BTnws provided the possibility that single PVDF molecular could wrap on its surface, but this molecular wrapping pattern would not occur when the diameter of BTnws was large. Besides, the wrapping pattern could be reinforced by interactions between surface hydroxyl groups of BTnws and F atoms of PVDF molecular. Such contributions could induce good interface compatibility and lead to the improvement of energy density.     

Core@double-shell structured fillers for increasing dielectric constant and suppressing dielectric loss of PVDF-based composite films

High dielectric constant polymer dielectrics have attracted a great deal of attention in flexible electronics. However, it appears to be a paradox for polymer dielectrics that the enhancement of their dielectric constant often comes along with the increase of dielectric loss. Hence, we reported core@double shell structured filler/poly(vinylidene fluoride) (PVDF) composites to overcome this paradox. The hybrid filler with BaTiO₃ (BT) as the core, conductive carbon as the inner shell, and insulating polydopamine (PDA) as the outer shell was synthesized. As a result, the BT@C@PDA/PVDF composites at the filler content of 11 vol% exhibit an outstanding dielectric performance with a dielectric constant of 45 and a dielectric loss of 0.053 at 10³ Hz. This phenomenon can be attributed to the increased interfacial polarization induced by the inner carbon shell and the conductive paths blockade caused by the outside PDA shell inside the BT@C@PDA/PVDF composites. This work reveals that rational design of core@double shell structured hybrid fillers maybe a promising way to optimize the overall dielectric performance of the PVDF-based composites.     

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.     

Tunable BaxSr1-xTiO3 nanoparticles induced high energy storage density in layer-structured asymmetric polymer-based nanocomposites

In order to solve the problem of low charging and discharging energy density of dielectric capacitors, the structure design of layered polymer matrix composites is carried out in this paper. Ba_0.7Sr_0.3TiO₃, Ba_0.8Sr_0.2TiO₃ and Ba_0.9Sr_0.1TiO₃ nanoparticles were successfully prepared by the oxalate coprecipitation method. The surface of Ba_xSr_1-xTiO₃ was successfully coated with dopamine, which promoted the dispersion of the polymer matrix of the ceramic powder. Monolayer Ba_xSr_1-xTiO₃/PVDF composites containing Ba_xSr_1-xTiO₃ with different Ba/Sr ratios were successfully prepared by the casting method. Three-layer asymmetric composites with different fillers were successfully prepared by layer-by-layer casting. The phase and microstructure of the as-prepared materials were analyzed by XRD and SEM. The dielectric, electrical conductivity, ferroelectric and energy storage properties of the composites were tested. The effects and laws of the design of the three-layer asymmetric structure on the dielectric properties and energy storage properties of the layered composites are mainly studied. When the structure of the three-layer asymmetric composite is 1-2-3, the breakdown field strength reaches 330 kV/mm, the discharge energy density reaches 8.51 J/cm³, and the charge-discharge efficiency is 67%. This work demonstrates that layered composites with asymmetric properties can facilitate the development of electrical energy storage.     

Improved dispersion and interfacial interaction of SiO2@polydopamine fillers in polytetrafluoroethylene composites for reduced thermal expansion and suppressed dielectric deterioration

Copper-clad laminate (CCL) comprised of copper foil and polytetrafluoroethylene (PTFE) faces severe thermal expansion mismatch due to the discrepancy in coefficient of thermal expansion (CTE) between the two components. Incorporating inorganic fillers with low CTE into PTFE has been proved to be a promising way to achieve the goal. However, it is a challenge to achieve homogeneous distribution and good interfacial interaction of fillers in PTFE composites owing to the characteristics of PTFE emulsion. In this work, core@shell structured SiO₂@polydopamine fillers (SiO₂@PDA) were synthesized and incorporated into PTFE matrix to form SiO₂@PDA/PTFE composites. Due to the presence of PDA shell, SiO₂@PDA exhibited improved dispersion and interfacial interaction, contributing to the reduced CTE and suppressed dielectric deterioration of SiO₂@PDA/PTFE composites. With 40 vol% of filler, the CTE of SiO₂@PDA/PTFE composite was efficiently reduced (50%), coupled with a limited sacrifice of only 2% and 40% of increments for dielectric constant (D_k, 2.3) and dielectric loss (D_f, 2.4 × 10⁻³), respectively (@40 GHz), as compared with that of the corresponding SiO₂/PTFE composite. The fillers and composites were comprehensively characterized to verify the mechanism of CTE and dielectric properties of the composites.     

Enhanced dielectric response of ternary polymeric composite films via interfacial bonding between V2C MXene and wide-bandgap ZnS

Increasing the dielectric constant of polymer/sulfide ceramic composites by using wide-bandgap semiconducting sulfide ceramic fillers like ZnS is difficult because of their low interface polarization. To increase the dielectric constant, in this study, ternary polymer-based composite films were designed and fabricated using a hybrid filler consisting of shell-like ZnS particles and core-like V₂C MXene particles. First, V₂C MXene with a multi-layered structure was synthesized from the simplest raw materials followed by the in-situ hydrothermal growth of ZnS particles around the V₂C particles. Then, binary polymer/ZnS and ternary polymer/V₂C–ZnS composites were fabricated, and their dielectric, conductive, and electrical breakdown properties were investigated. Finally, the effect of interfacial bonding between the V₂C and ZnS phases was investigated by density functional theory calculations, and the contribution of V₂C/ZnS interfacial bonding to the higher dielectric constant of the ternary composites than that of the binary composites was explained. The ternary composites exhibited balanced electrical properties suitable for energy storage applications. The ternary composite with 10 wt% hybrid filler loading exhibited a high dielectric constant of ~52, a low dielectric loss of ~0.11 at 100 Hz, and a high electrical breakdown strength of ~202 MV m⁻¹. This study paves the way for the facile fabrication of high-performance composite dielectrics for application in advanced capacitors.     

Structural,dielectric and mechanical behaviors of (La,Nb) Co-doped TiO2/Silicone rubber composites

Ceramic/polymer composites have great potential to achieve the concomitant enhancement of both dielectric constant and breakdown field while maintaining other superior properties of the polymer matrix, ideal for elastomer sensors, actuators, capacitive energy storage, and many other applications. However, material incompatibility between the ceramic filler and the polymer matrix often leads to void formation, particle aggregation and phase separation, with significantly degraded performance. Herein, through surface modification, co-doped TiO₂ particles were uniformly dispersed and bridged onto the silicone rubber matrix via a silane coupling agent for fabricating composites via mechanical mixing and hot-pressing. The synthesized composites exhibit enhanced dielectric constant, increased from 2.78 to 5.06 when 50 wt% co-doped TiO₂ particles are incorporated. Their dielectric loss is less than 0.001 in a broad frequency range. Theoretical modelling and experimental results reveal that the morphology and dispersion state of co-doped TiO₂ particles were crucial to the dielectric properties of the silicone rubber-based composites. Besides, the composites are thermally stable up to 400 °C. Significantly increased tensile strength (612 kPa) and elongation at break (330%) were obtained for the composite incorporated with 30 wt% co-doped TiO₂ particles, accompanied by a moderate increased elastic module (540 kPa). Such composites have the potential for different applications.     

Low dielectric loss LNT/PEEK composites with high mechanical strength and dielectric thermal stability

(3-Aminopropyl)triethoxysilane treated La_(2−x)/3Na_0.06TiO₃ (x = 0.06) (LNT) microparticles filled polyetheretherketone (PEEK) composites were prepared using hot pressing process. The effects of variation of LNT ceramic filling fraction on dielectric properties, water absorption, thermal stability and mechanical strength were investigated. All composites demonstrate low water absorption (less than 0.4%) when the ceramic filling fraction is lower than 0.6V_f. The obtained composites exhibited dielectric permittivities varying from ~4 to ~22 as the ceramic fillers increased from 0.1 to 0.8V_f and low losses (~10⁻⁴ @1 MHz, 3~5 × 10⁻³ at the frequencies of microwave (10 GHz) and millimeter wave (29-50 GHz), respectively). The mechanical strength, dimensional and dielectric thermal stability of the composite are remarkably improved by the addition of LNT ceramic fillers. A composite with near zero temperature coefficients of dielectric permittivity or resonant frequency and flexural strength of ~140 MPa could be obtained. The out-of-plane coefficient of thermal expansion (CTE) could be reduced to ~20 ppm/°C as the ceramic filler loading reached 0.7V_f.     

Core-shell structured BaTiO3@SiO2@PDA for high dielectric property nanocomposites with ultrahigh energy density

Flexible nanocomposite dielectrics with high dielectric constant and discharge energy density have broad application prospects in the field of energy storage. However, dielectrics with high dielectric constant tend to have a high dielectric loss. Herein, we prepared a dielectric composite material with ultra-high discharge energy density by modifying the interface between nanoparticles and poly(vinylidene fluoride-co-hexafluoropropylene) (P[VDF-HFP]). After coating a shell of insulating amorphous SiO₂ (~7 nm) outside the barium titanate (BT), the electric field concentration and current density inside BT particles can be significantly reduced. In addition, coating the SiO₂ shell with a polydopamine (PDA) shell (~7 nm) not only enhances the interface interaction between the nanoparticles and the polymer matrix, but also can form lots of microcapacitors in the composite. As a result, an ultra-high discharge energy density of 13.78 J/cm³ at the expense of relatively inconspicuous efficiency (~59.8%) in the BT@SiO₂@PDA/P (VDF-HFP) with 2.5 wt% loading has been achieved under 460 kV/mm. This is mainly attributed to the increases of dielectric constant from 12.1 to 14.2 and the relatively low dielectric loss (0.086) at 100 Hz. Moreover, compared with the pure P (VDF-HFP) (400 kV/mm), the breakdown voltage of the composite with 2.5 wt% loading is surged to 460 kV/mm, which benefited from the hindrance of nanoparticles on carrier migration at low content. This work has realized a thin-film dielectric with ultra-high discharge energy density through a novel design of the nanoparticle structure, providing a theoretical direction for the development of polymer dielectric capacitors.     

Improved dielectric properties and energy density of PVDF composites using PVP engineered BaTiO<Subscript>3</Subscript> nanoparticles

This work systematically investigates the effect of modifier polyvinylpyrrolidone (PVP) on the microstructure, dielectric and energy storage properties of BaTiO₃/PVDF composites. The results demonstrate that the BaTiO₃ nanoparticles modified by PVP are uniformly dispersed in the composites, and the defects including cracks and voids are obviously decreased in contrast to the composites with unmodified BaTiO₃ nanoparticles. Due to the enhanced interfacial polarization, the composites with BaTiO₃@PVP show improved dielectric properties compared with the composites with unmodified BaTiO₃ nanoparticles. For instance, at 1 kHz, the dielectric constant and dielectric loss of the composite with 50 vol% of BaTiO₃@PVP nanoparticles are 80.4 and 0.085, while of which the BaTiO₃/PVDF are 35 and 0.265, respectively. The discharge energy density of the composites is largely improved with PVP engineered BaTiO₃ nanoparticles. The composite with 30 vol% BaTiO₃@PVP achieves a discharged energy density of 4.06 J/cc at 240 kV/mm, which is 116% larger than that of pure PVDF (1.88 J/cc). This research provides an effect modifier to prepare high performance dielectric materials.     

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.     

Enhanced dielectric and mechanical properties of CaCu3Ti4O12/Ti3C2Tx MXene/silicone rubber ternary composites

Dielectric polymer composites with conducting fillers would have great potential for diverse applications if their severe leakage loss could be addressed. In this regard, ternary composites using both ceramic and conducting materials as fillers might be an enabler for high dielectric constant and low dielectric loss. Herein, ternary composites with both Ti₃C₂T_x MXene conducting nanosheets and CaCu₃Ti₄O₁₂ (CCTO) dielectric particles embedded in silicone rubber were studied. It was found that a ternary composite with 1.2 wt% (0.40 vol%) Ti₃C₂T_x MXene and 12 wt% (2.58 vol%) CCTO could provide an overall superior performance that include a high dielectric constant of 8.8, low dielectric loss of less than 0.0015, good thermal stability up to 450 °C, and excellent mechanical properties with tensile strength of 569 kPa, elastic module of 523 kPa and elongation at break of 333%. The outstanding performance is attributed to the improved uniform dispersion and good interfacial compatibility of mixed fillers in the polymer matrix, suggesting ternary composites might be a better option over their binary counterparts in preparing high performance dielectric composites.     

Polyvinylidene fluoride-modified BaTiO3 composites with high dielectric constant and temperature stability

Polyvinylidene fluoride (PVDF)-modified X7R-type BaTiO₃ (BTO) composites were prepared by hot pressing, and the dielectric properties were investigated. The dielectric constant of the PVDF–BTO composites at 1 kHz increased significantly with increasing the volume fraction of BTO up to 0.5, and good temperature stability of dielectric constant was obtained for the composites, which benefited from the temperature-stable dielectric constant of the modified BaTiO₃. Two significant dielectric relaxations were observed for the PVDF–BTO composites, and they fit the Vogel–Fulcher and Arrhenius fittings, respectively.     

Improved dielectric and mechanical properties of Ti3C2Tx MXene/silicone rubber composites achieved by adding a few boron nitride nanoplates

MXenes have attracted great attentions in the fabrication of dielectric polymer composites because of their excellent electrical conductivity. However, the high dielectric loss tangent would suppress the application of such polymer-based composites. Incorporating insulating fillers might be a solution. Herein, Ti₃C₂T_x MXene/silicone rubber (SR) composites incorporated with boron nitride (BN) nanoplates were prepared. The homogeneous distribution of fillers was obtained in the composites, which was also thermally stable up to 400 °C. Dielectric constant of 7.06 (2.54 times of pure SR) and dielectric loss tangent of 0.00131 were achieved when the filling contents of MXene and BN in SR composite were 1.2 wt% and 5 wt%, respectively. The improved dielectric constant can be ascribed to the enhanced interfacial polarization and the formation of conductive network, while the low dielectric loss tangent can be due to the insulating interlayers of BN which could inhibit the transfer of free electrons from conductive fillers to the insulating polymer matrices. BN/MXene/SR composites displayed improved mechanical properties (tensile stress of 671 kPa and elongation at break of 353%) and good flexibility (elastic modulus of 540 kPa) due to the low filling content of fillers. This work is promising for preparing dielectric polymer composites in applications of electronic devices.     

Novel polymer composites of RuO2@nBaTiO3/PVDF with a high dielectric constant

The dielectric properties of a novel polymer dielectric material were investigated. The conductive phase of RuO₂ was synthesized for deposition on the surface of a nanosized BaTiO₃ (nBT). The RuO₂@nBT hybrid particles were incorporated into a poly (vinylidene fluoride) (PVDF) as a three-phase composite (RuO₂@nBT/PVDF). The obtained dielectric constant (ε′) was significantly high (3837.16) for the composite with a volume fraction of $f_{Ru{O}_2@nBT}$ = 0.50. The large interfacial polarization between the RuO₂?nBT and RuO₂?PVDF interfaces considerably increased the value of ε′. Therefore, interfacial polarization is a critical factor in improving the dielectric properties. The dielectric behavior of the RuO₂@nBT/PVDF composites can be described using the effective medium percolation theory model, which indicates the significant contributions of the conductive RuO₂ phase and high-permittivity nBT phase.     

New composites with high thermal conductivity and low dielectric constant for microelectronic packaging

Three composites based on cyanate (CE) resin, aluminum nitride (AlN), surface‐treated aluminum nitride [AlN(KH560)], and silicon dioxide (SiO₂) for microelectronic packaging, coded as AlN/CE, AlN(KH560)‐SiO₂(KH560)/CE, and AlN‐SiO₂/CE composite, respectively, were developed for the first time. The thermal conductivity and dielectric constant of all composites were investigated in detail. Results show that properties of fillers in composites have great influence on the thermal conductivity and dielectric constant of composites. Surface treatment of fillers is beneficial to increase the thermal conductivity or reduce dielectric constant of the composites. Comparing with binary composite, when the filler content is high, ternary composites possess lower thermal conductivity and dielectric constant. The reasons leading to these outcomes are discussed intensively. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Achieving high breakdown strength and figure of merit of Ba0.6Sr0.4TiO3 films through coating a Y3Fe5O12 layer

Low tunability and figure of merit significantly limited the application of Ba_0.6Sr_0.4TiO₃ (BST) ferroelectric film, which originates from the low electric breakdown strength and high dielectric loss of BST layer. Garnet structured Y₃Fe₅O₁₂ (YIG) exhibits the merits of good microwave dielectric property and a much high resistivity, which are helpful for enhancing the breakdown strength and suppressing the dielectric loss. In this work, Y₃Fe₅O₁₂/Ba_0.6Sr_0.4TiO₃ (YIG/BST) composite films were fabricated via chemical solution deposition method. The composite films exhibited a low dielectric loss (0.006) and an almost frequency independent dielectric constant in a frequency range from 10 kHz to 1 MHz. The electric breakdown strength was significantly enhanced from less than 400 kV/cm to around 800 kV/cm through coating a YIG layer, causing an excellent tunability of 72.84% and an ultra-high figure of merit (FOM=118) at 800 kV/cm in YIG/BST film. It is physically clarified that the conduction loss plays an important role in BST film while the intrinsic loss is the dominate factor for the YIG/BST composite films.     

Effect of POSS‐grafted titanium dioxide on the electrical and thermal properties of LDPE/TiO2 polymer nanocomposite

Two types of nanocomposites have been fabricated by a ball‐milling technique. The first type consists of untreated titanium dioxide (TiO₂) incorporated into low‐density polyethylene (LDPE). For the second one, TiO₂ filler chemically treated with trisilanol phenyl–polyhedral oligomeric silsesquioxane (TP–POSS) as compatibilizing agent was ball‐milled with LDPE. All specimens were tested by microstructure analysis and thermal, dielectric characterization techniques. Microstructure analysis by atomic force microscopy and scanning electron microscopy show clearly an increased dispersion in presence of POSS. Scanning electron microscopy even shows the formation of a particular structure due possibly to interactions between functionalization. It was observed that the modification of the surface of TiO₂ by the POSS decreased the dielectric loss. All nanocomposites containing treated TiO₂ revealed an improvement in thermal conductivity, with the most distinct value of 19% in case of LDPE containing 5 wt % treated TiO₂. The incorporation of TiO₂ fillers seems to reduce the dielectric breakdown strength of the nanocomposites. However, nanocomposites containing 3 and 5 wt % treated TiO₂ have exhibited a slightly enhancement in dielectric breakdown strength up to 5%. The improvement in surface resistance to partial discharge was found in all nanocomposites specimens, especially for both types of composite containing 7 wt % untreated and treated TiO₂. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46095.     

Gradient dielectric constant sandwich-structured BaTiO3/PMMA nanocomposites with strengthened energy density and ultralow-energy loss

High energy storage density with low-energy loss polymer films are essential for high-performance electric devices. To avoid the high-energy loss of utilizing nonlinear polymer materials, a sandwich nanostructure comprising a linear polymer poly(methyl methacrylate) (PMMA) matrix embedded with a high dielectric constant BaTiO₃ (BT) interlayer and poly(vinylidene fluoride) (PVDF) binder was constructed using a solution casting strategy. This structural design takes advantage of each component in the composite. The good dispersion of BT particles in the binder, which was incorporated between PMMA, enabled a high dielectric constant and fewer defects. Additionally, the excellent film formation ability of the PVDF binder guarantees the uniform thickness and stable structure of the BT mid-layer, and good miscibility between PVDF and PMMA enhanced the interaction between each layer. Interestingly, since the dielectric constant of PVDF was between BT fillers and PMMA, a dielectric gradient distribution mitigated the local electric field concentration, as proven by the simulation results. Consequently, a low-loss linear PMMA composite film exhibited satisfying breakdown strength and excellent discharged energy density, which were 25% and 460% higher than those of pristine PMMA, respectively.