Enhanced dielectric permittivity of BaTiO3/epoxy resin composites by particle alignment

Barium titanate (BaTiO₃)/epoxy resin composites with a novel structure, in which the BaTiO₃ particles were directionally aligned in the epoxy resin matrix, were fabricated using the ice-templating method. The effects of the filler particle alignment and the filler fraction on the dielectric permittivity as well as the dielectric loss of the composites were studied. The results show that the aligning filler particles can significantly improve the dielectric permittivity while maintaining the dielectric loss compared with the traditional composite structure (homogeneously distributed). Due to the feasibility of the enhancement of the dielectric properties of the composites, the particle alignment that is achieved via the ice-templating method can be used in the field of high energy density capacitors.     

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.     

Effect of filler loading and thickness parameters on the microwave absorption characteristic of double-layered absorber based on MWCNT/BaTiO3/pitted carbonyl iron composite

In this work, single- and double-layer electromagnetic wave absorbers were prepared by as-prepared MWCNTs/BaTiO₃/pitted carbonyl iron composites. MWCNT/BaTiO₃ (MW/BTO) was prepared via sol-gel method whereas the carbonyl iron particles (CI) were corroded via pitting corrosion method. The structural, microstructural, magnetic and microwave absorption properties of the composites were evaluated via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA) methods. CST studio software was employed to simulate the microwave absorption characteristics of double-layer absorbers. Moreover, the effects of changing matching and absorbing layer thickness (3 mm in total) and filler loading (10, 20 and 30 wt%) of the as-prepared composite on the microwave absorption properties were investigated. According to the results, maximum RL value for single layer absorber with 20 wt% filler loading can reach ?11.5 dB at 9.7 GHz with 3 mm thickness and 0.4 GHz bandwidth. In contrast, double-layered absorber using 10 wt% of the composite in the upper layer (as matching layer) and 30 wt% of the composite in lower layer (as absorbing layer) can increase the reflection loss and absorption bandwidth values to ?15.5 dB and 1 GHz respectively. Improving in absorption characteristics can be attributed to coupling interactions, impedance matching and multiple scattering. The main advantages of the prepared double layer absorber than single layer absorber are tuning the intensity and effective absorption bandwidth by adjusting the layer order, thickness and filler loading of each layer which shown good potential for practical application.     

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.     

Effects of BaTiO3 and FeAlSi as fillers on the magnetic,dielectric and microwave absorption characteristics of the epoxy-based composites

A systematic study was carried out on the magnetic, dielectric and microwave absorption properties of the two-phase FeAlSi/epoxy and three-phase FeAlSi/BaTiO₃/epoxy composites through experimental and simulation method. A percolation effect was observed in the dielectric, but not in the magnetic behavior of the FeAlSi/epoxy composites when the FeAlSi content was high. The 2D modeling shows that the high electric energy density is responsible for the high permittivity near the percolation threshold (49 vol%). On the other hand, the permeability of the composites matches well with the effective medium theory model (EMT), indicating that the permeability of FeAlSi/epoxy composite is more associated with the filler size and shape. Theoretical calculations show that the increment of the FeAlSi and BaTiO₃ loading, as well as the thickness will cause the absorption peak position to shift to low frequencies. The microwave absorption of these composites can be mainly attributed to the dielectric loss and magnetic loss.     

A graphite nanoplatelet/epoxy composite with high dielectric constant and high thermal conductivity

A simple strategy for the preparation of composites with high dielectric constant and thermal conductivity was developed through a typical interface design. Graphite nanoplatelets (GNPs) with a thickness of 20–50 nm are fabricated and homogeneously dispersed in the epoxy matrix. A high dielectric constant of more than 230 and a high thermal conductivity of 0.54 W/mK (a 157% increase over that of pure epoxy) could be obtained for the composites with a lower filler content of 1.892 vol.%. The dielectric constant still remains at more than 100 even in the frequency range of 10⁵–10⁶ Hz. When loaded at 2.703 vol.%, GNP/epoxy composites have a dielectric constant higher than 140 in the frequency range of 10²–10⁴ Hz and a high thermal conductivity of 0.72 W/mK, which is a 240% increase over that of pure epoxy. The high dielectric constant and low loss tangent are observed in the composite with the GNPs content of 0.949 vol.% around 10⁴ Hz. It is believed that high aspect ratio of GNPs and oxygen functional groups on their basal planes are critical issues of the constitution of a special interface region between the GNPs and epoxy matrix and the high performance of the composites.     

Fabrication and origin of high-k carbon nanotube/epoxy composites with low dielectric loss through layer-by-layer casting technique

The distribution of polarized space charges and their relaxation behavior in high dielectric constant electric conductor/polymer composites are main factors that determine the frequency-dependent dielectric constant and dielectric loss. However, few reports focus on this motif. We present here the dielectric performance and mechanism of a unique kind of composites with multi-layers (coded as [MWCNT/EP]_x, where x refers to the number of layers), fabricated by using layer-by-layer casting technique. Each composite layer with same thickness was composed of multi-walled carbon nanotubes (MWCNTs) and epoxy (EP) resin. When the loading of MWCNTs is 0.5 wt%, the four-layer [MWCNT0.5/EP]₄ material shows the highest dielectric constant (465 at 1 Hz) and low dielectric loss tangent (0.7 at 1 Hz), about 4 and 2.1 × 10⁻² times the values of traditional MWCNT0.5/EP composite, respectively. By investigating the space charge polarization (SCP), Debye polarization and dielectric moduli in [MWCNT/EP]_x materials, the complex relationships and the origin among dielectric constant, dielectric loss, frequency and the content of filler were clearly elucidated. The SCP within each layer is different from that between layers. The greatly improved dielectric properties of [MWCNT/EP]_x materials are believed to be the reinforced SCP and blocked transport of carriers between every two layers.     

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.     

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.     

BaTiO3 nanocubes-Gelatin composites for piezoelectric harvesting: Modeling and experimental study

Flexible composites containing BaTiO₃ nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO₃ nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO₃ addition), permittivity reaches ε_r ～15.7 with respect to ε_r ～9.8 of pure Gelatine (measured at 10⁵ Hz), while the average piezoelectric coefficient d₃₃ as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to ～7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.     

Optical properties of multi-stacked BaTiO3/SrTiO3 thin films synthesized via chemical method

In this work, the BaTiO₃ and SrTiO₃ thin films as well as BaTiO₃/SrTiO₃ lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO₃, but cubic structure for SrTiO₃. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO₃ samples and from 4.13 eV to 3.80 eV for SrTiO₃ samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO₃, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO₃ and SrTiO₃. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO₃ sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied.     

Thermomechanically stable dielectric composites based on poly(ether ketone) and BaTiO3 with improved electromagnetic shielding properties in X‐band

High‐performance barium titanate (BaTiO₃) filled poly(ether ketone) (PEK) composites were prepared by melt compounding with an aim to investigate the effect of BaTiO₃ on thermal, thermomechanical, dielectric, and electromagnetic interference shielding behavior of PEK. The content of BaTiO₃ in the PEK matrix was varied from 0 to 18 vol %. Scanning electron microscopy studies shows that BaTiO₃ particles were uniformly distributed in the PEK matrix up to 13 vol % loading followed by the formation of agglomerates at higher loading (18 vol %). Rockwell hardness increased up to 13 vol % loading followed by a decrease at 18 vol % loading. Dynamic mechanical analysis revealed that storage modulus increases with increase in BaTiO₃ loading with a maximum value of 3192 MPa at 13 vol % compared to 2099 MPa for neat PEK. Dielectric constant of composites measured in the frequency range of 8.2–12.4 GHz increased approximately three times upon incorporation of 18 vol % of BaTiO₃. This increment in dielectric constant is reflected in improved electromagnetic shielding properties as loading of dielectric filler (BaTiO₃) increases. Total shielding effectiveness of ?11 dB (～92% attenuation) at loading of 18 vol % BaTiO₃ justifies the use of these composites for suppression of EM radiations. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46413.     

Multifunctional fiberglass-reinforced PMMA-BaTiO3 structural/dielectric composites

Fiberglass-reinforced polymer composites were investigated for potential use as structural dielectrics in multifunctional capacitors that require simultaneous excellent mechanical properties and good energy storage characteristics. Composites were fabricated employing poly(methyl methacrylate), PMMA, as the structural matrix. While barium titanate (BaTiO₃) nanopowder was added to the composites for its high room temperature dielectric constant, fiberglass was employed to confer high stiffness. A conductive polymer blend of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) was used to coat the BaTiO₃ nanoparticles with the purpose of further elevating the dielectric constant of the resultant PMMA-composites. FTIR spectroscopy, TGA and SEM measurements were conducted to prove the successful coating of BaTiO₃ nanoparticles with the PEDOT:PSS blend. TEM measurements revealed a good dispersion of coated nanoparticles throughout the PMMA matrix. The fiberglass-reinforced-PMMA composites containing neat and coated BaTiO₃ were found to exhibit excellent stiffness. In addition, the use of PEDOT:PSS in conjunction with BaTiO₃ was observed to improve the dielectric constant of the composites. Finally, the dielectric constant of the structural composites was found to vary only slightly with temperature.     

Flexible 0–3 Ceramic‐Polymer Composites of Barium Titanate and Epoxidized Natural Rubber

Flexible composites with a high electrical permittivity are pursued in materials research, due to their potential applications in electrical devices. We synthesized such ceramic‐polymer composites from BaTiO₃ and epoxidized natural rubber. The influence of BaTiO₃ concentration on cure characteristics, mechanical (static & dynamic), dielectric, and morphological properties of the composites was investigated. The tensile strength and elongation at break decreased with BaTiO₃ loading, while the storage modulus and permittivity of composites increased. As for dynamic electrical properties, the dielectric loss factor and tan δ of the composites showed a maximum peak within the frequency range extending up to 10⁵ Hz, reflecting the relaxation process of the polymer matrix. All of the composites showed two peaks in the frequency dependence of electric modulus, due to conductivity and molecular relaxation. Scanning electron microscopy micrographs confirmed the 0–3 structure of composites, with isolated BaTiO₃ particles.     

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.     

Dielectric properties of polymer/ceramic composites based on thermosetting polymers

Summary A series of thermosetting polymer/ceramic composites were prepared. Three kinds of thermosetting polymers, i.e. cyanate resin, bismaleimide resin, and epoxy resin, were used as matrixes, and BaTiO₃ particles were as fillers. The dielectric properties of these composites were investigated. Experimental data of the dielectric constants were fitted to several theoretical equations in order to obtain the best-fitting equations of the dielectric constants of these composites. The result indicates that the dielectric constants of composites all increase with the increase of BaTiO₃ content. Using bismaleimide resin and epoxy resin as matrixes, the dielectric losses both increase obviously as the amount of BaTiO₃ particles is increased, but the dielectric loss of cyanate/BaTiO₃ composite decreases. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of cyanate/BaTiO₃ composite are both the smallest. The predications of the effective dielectric constants by Lichterecker mixing rule are in good agreement with experiment data.     

Microwave dielectric properties of PTFE/CaTiO3 polymer ceramic composites

CaTiO₃ ceramic powder filled polytetrafluoroethylene (PTFE) composites with various filler volume fractions up to 60 vol.% were prepared. The effects of volume fraction of the ceramic filler on the microstructure and microwave dielectric properties of the composites were investigated in detail. As the volume fraction of the ceramic filler increases, the dielectric constant (?_r) and the temperature coefficient of resonant frequency (τ_f) of composites increase, while the product of quality factor and frequency (Q × f) decreases. Composites with 40 vol.% CaTiO₃ exhibited good microwave dielectric properties: ?_r = 13 at ∼5 GHz, Q × f = 930 GHz, and τ_f = 260 ppm/°C. Different mixing rules were used to predict the dielectric constant of composites, and it was found that the dielectric constants predicted by Effective Medium Theory (EMT) were in good agreement with experimental data.     

Characteristics of polyimide/barium titanate composite films

In this study, the characteristics of the polyimide/BaTiO₃ composite films with various amounts of BaTiO₃ were evaluated. Modifier 1-methoxy-2-propyl acetate was added during composite preparation to disperse the BaTiO₃ particles in polyimide matrix. Conversion of polyamic acid (PAA) to polyimide was not completed for the composite film with a high BaTiO₃ loading (90 wt%). Dielectric constant of the film increases from 3.53 to 46.50, at the sweep frequency of 10 kHz, as the BaTiO₃ content increases from 0 to 90 wt% (0–67.5 vol.%), which is mainly due to the relatively high dielectric constant of BaTiO₃ particles in the polyimide matrix. The dielectric losses at 10 kHz is ranging from 0.005 to 0.015, which is due to the switching of the domain wall. Water absorption decreases considerably with increasing BaTiO₃ content. With 10 wt% (2.5 vol.%) BaTiO₃ addition, the water absorption of the composite film reduces 45% from that of pure polyimide. Also, high loading of BaTiO₃ is not beneficial to reduce the water absorption of the composite film.     

Rheological,mechanical, and electrical properties of Sr0.7Bi0.2TiO3 modified BaTiO3 ceramic and its composites

Porous BaTiO₃-based relaxor ferroelectric ceramics with lamellar structure were achieved by ice templating method, and the rheological properties of ceramic slurry for freeze casting were deeply studied. Epoxy resin was then backfilled to generate ceramic–epoxy resin composites. Ceramic–epoxy composites with a lamellar structure were obtained when using a slurry with a ceramic content of 45 wt.%. The nanoindentation results showed that the introduction of ceramic materials into the epoxy resin can significantly improve the penetration resistance and hardness of the material. The dielectric and ferroelectric properties of the composites were also characterized. The interaction between the highly coupled dipoles in the polymers results in a decrease in the breakdown field strength of the composite. The dielectric constant reached up to ∼800. At 220 kV/cm, W_rec = 0.62 J/cm³, and η was ∼80%. At low frequencies, W_rec was ∼0.16 J/cm³, which indicated good stability.     

Barium titanate‐based nanodielectrics of two chemically recyclable thermosets

In this work was investigated the effect of the addition of barium titanate (BaTiO₃) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO₃‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10^?8 S m^?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO₃ ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (10² Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (T_g) values in the range 125–180 °C. An increase of 7 °C in T_g was observed after the incorporation of 0.5 wt% of BaTiO₃ into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO₃. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry