Showing papers on "Dielectric loss published in 2014"

Exploring Strategies for High Dielectric Constant and Low Loss Polymer Dielectrics.

Abstract: Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization or dielectric constant tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this Perspective, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach.

Topological‐Structure Modulated Polymer Nanocomposites Exhibiting Highly Enhanced Dielectric Strength and Energy Density

Abstract: Dielectric materials with high electric energy densities and low dielectric losses are of critical importance in a number of applications in modern electronic and electrical power systems. An organic–inorganic 0–3 nanocomposite, in which nanoparticles (0-dimensional) are embedded in a 3-dimensionally connected polymer matrix, has the potential to combine the high breakdown strength and low dielectric loss of the polymer with the high dielectric constant of the ceramic fillers, representing a promising approach to realize high energy densities. However, one significant drawback of the composites explored up to now is that the increased dielectric constant of the composites is at the expense of the breakdown strength, limiting the energy density and dielectric reliability. In this study, by expanding the traditional 0–3 nanocomposite approach to a multilayered structure which combines the complementary properties of the constituent layers, one can realize both greater dielectric displacement and a higher breakdown field than that of the polymer matrix. In a typical 3-layer structure, for example, a central nanocomposite layer of higher breakdown strength is introduced to substantially improve the overall breakdown strength of the multilayer-structured composite film, and the outer composite layers filled with large amount of high dielectric constant nanofillers can then be polarized up to higher electric fields, hence enhancing the electric displacement. As a result, the topological-structure modulated nanocomposites, with an optimally tailored nanomorphology and composite structure, yield a discharged energy density of 10 J/cm3 with a dielectric breakdown strength of 450 kV mm–1, much higher than those reported from all earlier studies of nanocomposites.

Fabrication, characterization, properties and theoretical analysis of ceramic/PVDF composite flexible films with high dielectric constant and low dielectric loss

Abstract: Calcium barium zirconate titanate (Ba0.95Ca0.05Zr0.15Ti0.85O3, BCZT) ceramic particles were prepared by a conventional solid-state method. BCZT powders were modified by dopamine through a chemical coating method. The composite flexible films based on dopamine@BCZT and polyvinylidene fluoride were fabricated via a solution casting method. The microstructure and morphology were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. A precision impedance analyzer and a dielectric withstand voltage test were used to test the dielectric constant, loss tangent, and breakdown strength. TEM results showed that dopamine was uniformly coated on the surface of BCZT particles with an average thickness of 20 nm. SEM results showed that the ceramic particles were dispersed homogeneously in the matrix. The dielectric constant increased with the increase of BCZT contents, while the loss tangent remained constant in the frequency range of 103 to 105 Hz. Different theoretical models were employed to predict the effective dielectric constants of the composite films, and the estimated results were compared with the experimental data. Weibull distribution was used to analyze the dielectric breakdown strength, and the results showed that the breakdown strength decreased then stayed over 60 kV mm−1.

Nano Ag-Deposited BaTiO3 Hybrid Particles as Fillers for Polymeric Dielectric Composites: Toward High Dielectric Constant and Suppressed Loss

Abstract: Nano Ag-deposited BaTiO3 (BT-Ag) hybrid particles usable as fillers for flexible polymeric composites to obtain high dielectric constant, low conductivity, and low dielectric loss were developed. BT-Ag hybrid particles were synthesized via a seed-mediated growing process by a redox reaction between silver nitrate and ethylene glycol. Nano Ag particles with a size less than 20 nm were discretely grown on the surface of the 100 nm BaTiO3. The similar lattice spacing of the (1 1 1) planes of BT and Ag led to the hetero-epitaxial growth of Ag on the BT surface. The thickness of the coherent interface was about 3 nm. The adhesion of Ag to BT efficiently prevented the continuous contact between Ag particles in the polyvinylidene fluoride (PVDF) matrix and suppressed the formation of the conducting path in the composite. As a result, with a filler loading of 43.4 vol %, the composite exhibited a dielectric constant (Dk) value of 94.3 and dielectric loss (tan δ) of 0.06 at 1 kHz. An even higher Dk value of 160 at...

Graphene–carbonyl iron cross-linked composites with excellent electromagnetic wave absorption properties

Abstract: Graphene is a highly desirable material for efficient electromagnetic wave absorption due to its strong dielectric loss and low density. However, the main drawbacks in pristine graphene, such as high dielectric constant and low permeability, inevitably limit its performance due to the poor impedance matching. In this paper, reduced graphene oxide–spherical carbonyl iron composites (RGO–SCI) have been successfully fabricated through a facile wet chemical method. As expected, an apparent improvement of impedance matching in electromagnetic wave absorption could be found through the combination of RGO and SCI. A carbon-bridge effect was adopted to explain the electromagnetic wave absorbing process, which is closely related to a cross-linked framework structure of as-synthesized composites. Besides, in the range of 7.79–11.98 GHz with the thickness of 3.0 mm, the RGO–SCI composites exhibited efficient electromagnetic wave absorption characteristics (RL < 10 dB) with a minimum reflection loss of −52.46 dB.

“Grafting to” route to PVDF-HFP-GMA/BaTiO3 nanocomposites with high dielectric constant and high thermal conductivity for energy storage and thermal management applications

Abstract: The introduction of high dielectric constant ceramic nanoparticles into an insulating polymer is an important approach to prepare high dielectric constant nanocomposites for electric energy storage applications. A key to obtaining desirable properties is the homogeneous dispersion of the nanoparticles in the corresponding polymer. Conventional methods used to improve the nanoparticle dispersion enhance the physical interaction between the nanoparticle and the polymer matrix via nanoparticle surface modification. In this work, the covalent bonding between the nanoparticle and the polymer matrix was utilized to simultaneously enhance the nanoparticle dispersion and nanoparticle/polymer interaction by functionalizing both the polymer and the nanoparticles. The poly(vinylidene fluoride-co-hexafluoropropylene) [PVDF-HFP] was functionalized with glycidyl methacrylate (GMA) via atom transfer radical polymerization. The barium titanate (BaTiO3) nanoparticles were modified by amino-terminated silane molecules. Then the nanocomposites were prepared by a “grafting to” method. Namely, grafting GMA functionalized PVDF-HFP to the surfaces of the BaTiO3 nanoparticles. The introduction of GMA into the PVDF-HFP not only increases the dielectric constant, but also changes the dielectric response of PVDF-HFP. More importantly, this “grafting to” approach results in core–shell structured BaTiO3@PVDF-HFP-GMA and thus a homogeneous dispersion of BaTiO3 nanoparticles in the nanocomposites. The dielectric constant, electric energy density and thermal conductivity of the nanocomposites are significantly enhanced with the increase of BaTiO3, while the dielectric loss shows a slight decrease as the nanoparticle loading increases.

Structural and optical characterization of Cr2O3 nanostructures: Evaluation of its dielectric properties

Abstract: The structural, optical and dielectric properties of as-grown Cr2O3 nanostructures are demonstrated in this paper. Powder X-ray diffractometry analysis confirmed the rhombohedral structure of the material with lattice parameter, a = b = 4.953 A; c = 13.578 A, and average crystallize size (62.40 ± 21.3) nm. FE-SEM image illustrated the mixture of different shapes (disk, particle and rod) of as-grown nanostructures whereas; EDS spectrum confirmed the elemental purity of the material. FTIR spectroscopy, revealed the characteristic peaks of Cr–O bond stretching vibrations. Energy band gap (3.2 eV) of the nanostructures has been determined using the results of UV-VIS-NIR spectrophotometer. The dielectric properties of the material were checked in the wide frequency region (100Hz-30 MHz). In the low frequency region, the matrix of the dielectric behaves like source as well as sink of electrical energy within the relaxation time. Low value of dielectric loss exhibits that the materials posses good optical quality with lesser defects. The ac conductivity of the material in the high frequency region was found according to frequency power law. The physical-mechanism and the theoretical-interpretation of dielectric-properties of Cr2O3 nanostructures attest the potential candidature of the material as an efficient dielectric medium.

Microstructure and dielectric properties of (Nb + In) co-doped rutile TiO2 ceramics

Abstract: The (Nb + In) co-doped TiO2 ceramics recently attracted considerable attention due to their colossal dielectric permittivity (CP) (∼100,000) and low dielectric loss (∼0.05). In this research, the 0.5 mol. % In-only, 0.5 mol. % Nb-only, and 0.5–7 mol. % (Nb + In) co-doped TiO2 ceramics were synthesized by standard conventional solid-state reaction method. Microstructure studies showed that all samples were in pure rutile phase. The Nb and In ions were homogeneously distributed in the grain and grain boundary. Impedance spectroscopy and I-V behavior analysis demonstrated that the ceramics may compose of semiconducting grains and insulating grain boundaries. The high conductivity of grain was associated with the reduction of Ti4+ ions to Ti3+ ions, while the migration of oxygen vacancy may account for the conductivity of grain boundary. The effects of annealing treatment and bias filed on electrical properties were investigated for co-doped TiO2 ceramics, where the electric behaviors of samples were found to be susceptible to the annealing treatment and bias field. The internal-barrier-layer-capacitance mechanism was used to explain the CP phenomenon, the effect of annealing treatment and nonlinear I-V behavior for co-doped rutile TiO2 ceramics. Compared with CaCu3Ti4O12 ceramics, the high activation energy of co-doped rutile TiO2 (3.05 eV for grain boundary) was thought to be responsible for the low dielectric loss.

Combining RAFT polymerization and thiol-ene click reaction for core-shell structured polymer@BaTiO3 nanodielectrics with high dielectric constant, low dielectric loss, and high energy storage capability.

Abstract: Nanodielectric materials with high dielectric constant, low dielectric loss, and high energy storage capability are highly desirable in modern electric and electronics industries. It has been proved that the preparation of core–shell structured dielectric polymer nanocomposites via “grafting from” method is an effective approach to these materials. However, by using this approach, the deep understanding of the structure–dielectric property relationship of the core–shell structured nanodielectrics has been limited because of the lack of detailed information (e.g., molecular weight, grafting density) about the macromolecules grafted onto the nanoparticle surfaces. In this work, by the combination of reversible addition–fragmentation chain transfer (RAFT) polymerization and thiol–ene click reaction, two types of core–shell structured polymer@BaTiO3 (polymer@BT) nanocomposites with high dielectric constant and low dielectric loss were successfully prepared via a “grafting to” method. Compared with the “grafti...

Fluoro-polymer functionalized graphene for flexible ferroelectric polymer-based high-k nanocomposites with suppressed dielectric loss and low percolation threshold.

Abstract: Flexible nanodielectric materials with high dielectric constant and low dielectric loss have huge potential applications in the modern electronic and electric industry. Graphene sheets (GS) and reduced-graphene oxide (RGO) are promising fillers for preparing flexible polymer-based nanodielectric materials because of their unique two-dimensional structure and excellent electrical and mechanical properties. However, the easy aggregation of GS/RGO significantly limits the potential of graphene in enhancing the dielectric constant of polymer composites. In addition, the poor filler/matrix nanoscale interfacial adhesion also causes difficulties in suppressing the dielectric loss of the composites. In this work, using a facile and environmentally friendly approach, polydopamine coated RGO (PDA-RGO) and fluoro-polymer functionalized RGO (PF-PDA-RGO) were prepared. Compared with the RGO prepared by the conventional methods [i.e. hydrazine reduced-graphene oxide (H-RGO)] and PDA-RGO, the resulting PF-PDA-RGO nanosheets exhibit excellent dispersion in the ferroelectric polymer matrix [i.e. poly(vinylidene fluoride-co-hexafluoro propylene), P(VDF-HFP)] and strong interfacial adhesion with the matrix, leading to a low percolation threshold (fc = 1.06 vol%) and excellent flexibility for the corresponding nanocomposites. Among the three nanocomposites, the P(VDF-HFP)/PF-PDA-RGO nanocomposites exhibited the optimum performance (i.e. simultaneously having high dielectric constant and low dielectric loss). For instance, at 1000 Hz, the P(VDF-HFP) nanocomposite sample with 1.0 vol% PF-PDA-RGO has a dielectric constant of 107.9 and a dielectric loss of 0.070, showing good potential for dielectric applications. Our strategy provides a new pathway to prepare high performance flexible nanodielectric materials.

Studies on the dielectric properties of CdS nanoparticles

Abstract: CdS is one of the most important II-VI semi- conductors with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized by the wet chemical method. The crystal structure and grain size of the particles were determined by X-ray diffraction. The optical properties were studied by the ultraviolet-visible absorption spectrum. The dielectric properties of CdS nanoparticles were studied in the fre- quency range of 50 Hz-5 MHz at different temperatures. The frequency dependence of the dielectric constant and dielectric loss is found to decrease with an increase in the frequency at different temperatures. The dielectric prop- erties of CdS nanoparticles are found to be significantly enhanced specially in the low frequency range due to confinement. Further, electronic properties, such as valence electron plasma energy, average energy gap or Penn gap, Fermi energy and electronic polarizability of the CdS nanoparticles were calculated. The AC electrical conduc- tivity measurements reveal that the conduction depends on both the frequency and the temperatures.

Enhanced dielectric properties of amino-modified-CNT/polyimide composite films with a sandwich structure

Abstract: Novel amino-modified-CNT/polyimide (NH2-MWNT/PI) flexile composite films with a sandwich structure were prepared through step-by-step casting, in which a dielectric layer (NH2-MWNT/PI composites) intercalated between the two insulating layers (pure PI, acting as both the bottom and the top layers). Due to the high capacitance of the dielectric layer and the effective blocking off conductive paths by the insulating layers, the sandwich composite films show a high dielectric constant and ultralow dielectric loss, and the dielectric constants of the composite films are almost frequency independent between 1 and 1000 kHz. It is notable that the NH2-MWNT/PI ratio of the mid-layer markedly influences the dielectric property of the composite film. When the NH2-MWNT content of the mid-layer is 10 wt%, the multi-layer composite film (P-10-P) shows the highest dielectric constant (e′) of 31.3 at 1 kHz, while the dielectric loss (tan δ) of the P-10-P is only 0.0016. Furthermore, the obtained multi-layer composite films have high breakdown strength and maximum energy storage density. The mechanical properties and thermal properties of the composite films were also examined in this work.

Enhanced Dielectric Performance in Polymer Composite Films with Carbon Nanotube‐Reduced Graphene Oxide Hybrid Filler

Abstract: The electrical conductivity and the specific surface area of conductive fillers in conductor-insulator composite films can drastically improve the dielectric performance of those films through changing their polarization density by interfacial polarization. We have made a polymer composite film with a hybrid conductive filler material made of carbon nanotubes grown onto reduced graphene oxide platelets (rG-O/CNT). We report the effect of the rG-O/CNT hybrid filler on the dielectric performance of the composite film. The composite film had a dielectric constant of 32 with a dielectric loss of 0.051 at 0.062 wt% rG-O/CNT filler and 100 Hz, while the neat polymer film gave a dielectric constant of 15 with a dielectric loss of 0.036. This is attributed to the increased electrical conductivity and specific surface area of the rG-O/CNT hybrid filler, which results in an increase in interfacial polarization density between the hybrid filler and the polymer.

Facile preparation of uniform barium titanate (BaTiO3) multipods with high permittivity: impedance and temperature dependent dielectric behavior

Abstract: Perovskite barium titanate (BaTiO3) multipods were prepared via high temperature solid state reaction. The crystal structure and morphology of BaTiO3 particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and scanning probe microscopy (SPM). The XRD analysis of the crystal structure revealed that a single-phase compound was formed having tetragonal crystal structure. Calorimetric study (DSC) over room to high temperature was used to find the energy involved in different steps of synthesis especially during the initiation and the termination process for the formation of BaTiO3. These multipods have high average aspect ratio (∼10, where average diameter ∼300 nm and average length ∼3 μm) as seen from FESEM. UV-Vis spectroscopy reveals that the prepared material is UV active. The bulk and surface chemical composition of these BaTiO3 particles as investigated by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra reveals that in the prepared BaTiO3, the titanium ions exist in two different oxidation states, namely Ti3+ and Ti4+. The BaTiO3 multipod exhibits high permittivity with relatively low dielectric loss. From impedance analysis of the material, the dual resistivity characteristics, one for grain and the other for grain-boundary can be distinguished. An equivalent circuit has been proposed through analysis of the complex impedance plot (Nyquist plot) for BaTiO3 multipods. This material has perfect capacitative nature as seen from the Bode plot, and can be used for charge storage devices and other electronic applications. From temperature dependent dielectric analysis, the Curie temperature of BaTiO3 multipods is found to be ∼85 °C.

Dielectric and microwave-absorption properties of SiC nanoparticle/SiBCN composite ceramics

Abstract: SiC nanoparticles with different contents (5–20 wt%) were mixed with liquid polyborosilazane. The compound was used to prepare SiC nanoparticle/polymer-derived SiBCN ceramics (SiC/PDCs-SiBCN). Thermal gravity tests (25–1400 °C) in air and helium atmosphere were used to investigate the thermal stability of SiC/PDCs-SiBCN. Dielectric and microwave-absorption properties of SiC/PDCs-SiBCN were determined at frequencies of 8.2–12.4 GHz by waveguide method. Results show that the addition of SiC nanoparticles increased the thermal stability of SiBCN ceramics. The permittivity, dielectric loss and absorption coefficient of ceramics increased as an elevated SiC content, resulting from the increase of carrier concentration. To understand the high-temperature dielectric property of SiC/PDCs-SiBCN, the permittivity of SiBCN ceramics with 15 wt% of SiC was measured at temperatures of 293–773 K. The composite ceramics were found to have a visible increase in the permittivity and dielectric loss, indicating their great potential as the high-temperature microwave absorption materials.

Effect of Pore Morphology on the Dielectric Properties of Porous Carbons for Microwave Absorption Applications

Abstract: The porous carbons (PCs) with tunable morphologies and pore sizes were prepared by the sol–gel process via a freeze-drying technique for microwave absorption applications. The results of Raman spectroscopy and nitrogen sorption analysis showed that the graphitization degree was barely influenced as the ratio of tert-butanol (T) to resorcinol (R) decreased, while the pore morphologies changed from the disordered slit-shaped pores to the uniform cage-like pores. Dielectric properties of the as-prepared carbon samples were determined by a vector network analyzer in the frequency range of 8.2–12.4 GHz. Results showed that the effect of pore morphology on the dielectric loss of PCs was dominant in the case of similar graphitization. When the T/R ratio was 7.5, the sample with cage-like pores revealed the maximum values in the real part e′ and the imaginary part e″ of complex permittivity, which were 13.2–6.5 and 15.6–10.1, respectively, suggesting a better capacity of dielectric loss in the 8.2–12.4 GHz range....

Giant permittivity and low dielectric loss of SrTiO3 ceramics sintered in nitrogen atmosphere

Abstract: The dielectric properties of SrTiO 3 ceramics sintered in nitrogen (N 2 ) exhibit a weak temperature- and frequency-dependent giant permittivity (>10 4 ) as well as a very low dielectric loss (mostly

Room temperature lead-free relaxor–antiferroelectric electroceramics for energy storage applications

Abstract: Round the globe, scientific communities have been searching for new materials for “green” energy, producing efficiently both high power as well as high energy density. Relaxor ferroelectrics (RFEs) have shown immense potential to achieve this goal. We report fabrication of [Na0.42Bi0.44Al0.06Ba0.08)TiO3 (NBAT–BT)], a lead-free-relaxor antiferroelectric ceramic, via a conventional solid-state reaction method. A small fraction of trivalent cations (Al3+) doping at Na1+/Bi3+ sites develop anti-polar phase in the ferroelectric matrix which in turn changes its functional properties. Rietveld refinement suggests the existence of both tetragonal and rhombohedral phases which is well supported by d-spacing values obtained in high resolution transmission electron microscopy (HRTEM) studies. Elemental analysis confirms the stoichiometry of the system and matches the starting composition well within the experimental uncertainty (±10%) of secondary electron microscopy (SEM) and HRTEM data. Raman spectra suggest the substitution of Al3+ cation at an A-site sublattice. Temperature-dependent dielectric spectra show frequency dependent dielectric dispersion near 80–110 °C, high dielectric loss at high probing frequency, and a non-linear Vogel–Fulcher relation, substantiating the relaxor–antiferroelectric (r-AFE) nature of NBAT–BT. A second order diffuse anti/ferro-electric to paraelectric phase transition near 230–240 °C was observed which follows a modified Curie–Weiss law. The energy density was calculated from polarization–electric field (P–E) loops and dielectric–electric field (e–E) plot. The values were in the range of 0.4–0.6 J cm−3, which is reasonably good for bulk polar material. NBAT–BT shows a much thinner AFE hysteresis above its relaxor FE phase transition; that favors the enhanced energy storage capacity at elevated temperature in the depolarized paraelectric region.

Amplifying dynamic nuclear polarization of frozen solutions by incorporating dielectric particles.

Abstract: There is currently great interest in understanding the limits on NMR signal enhancements provided by dynamic nuclear polarization (DNP), and in particular if the theoretical maximum enhancements can be achieved. We show that over a 2-fold improvement in cross-effect DNP enhancements can be achieved in MAS experiments on frozen solutions by simply incorporating solid particles into the sample. At 9.4 T and similar to 105 K, enhancements up to epsilon(H) = 515 are obtained in this way, corresponding to 78% of the theoretical maximum. We also underline that degassing of the sample is important to achieve highest enhancements. We link the amplification effect to the dielectric properties of the solid material, which probably gives rise to scattering, diffraction, and amplification of the microwave field in the sample. This is substantiated by simulations of microwave propagation. A reduction in sample heating at a given microwave power also likely occurs due to reduced dielectric loss. Simulations indicate that the microwave field (and thus the DNP enhancement) is inhomogeneous in the sample, and we deduce that in these experiments between 5 and 10% of the solution actually yields the theoretical maximum signal enhancement of 658. The effect is demonstrated for a variety of particles added to both aqueous and organic biradical solutions.

Solvothermal synthesis of CoxFe3−xO4 spheres and their microwave absorption properties

Abstract: CoxFe3−xO4 (x = 0–1) spheres are synthesized via a solvothermal reaction using ethylene glycol (EG) as a solvent They are characterized, and the results show that the prepared spheres are mainly 300–500 nm in diameter and constituted by small grains For the EG solution containing stoichiometric ingredients (atomic ratio of Co2+:Fe3+ = 1:2), the obtained spheres are Co09Fe21O4 at 200 °C (sphere A) and Co074Fe226O4 (sphere B) at 300 °C, whose crystallites are 23 nm and 30 nm in size, respectively VSM measurements reveal improved properties with sphere B Variations of complex permittivity and permeability for different composite (75% mass ratio of spheres) have been studied as a function of frequency The calculated reflectivity value indicates that the composite containing sphere A displays better microwave absorption capability The minimum reflection loss reaches −41089 dB at 1208 GHz, with a matching thickness of 2 mm The dielectric loss contributes even more than magnetic loss in the frequency range of 3–14 GHz The synergistic effect of dual losses makes the submicrosphere a promising absorbent in X and Ku bands The composite consisting of sphere B is inferior in dielectric properties owing to ferrous ion migration from octahedral to tetrahedral sites and due to the big crystallites lacking defects After the calcination treatment of the spheres at 700 °C, the dielectric loss turns out to be low due to the disappearing Fe2+ ↔ Fe3+ pairs in adjacent octahedral sites and the loss of defects Variations of the cobalt ratio in spheres can change the resonance frequency and crystallinity of the spheres and ultimately the minimum reflection loss and corresponding frequency band The microwave absorption properties of mixed magnetite and cobalt ferrite spheres are influenced by the cationic stoichiometry and crystalline integrity

Preparation process and dielectric properties of Ba0.5Sr0.5TiO3–P(VDF–CTFE) nanocomposites

Abstract: Ceramic-polymer 0-3 nanocomposites, in which nanosized Ba(0.5)Sr(0.5)TiO3 (BST) powders were used as ceramic filler and P(VDF-CTFE) 88/12 mol% [poly(vinylidene fluoridechlorotrifluoroethylene)] copolymer was used as matrix, were studied over a concentration range from 0 to 50 vol.% of BST powders. It is found that the solution cast composites are porous and a hot-press process can eliminate the porosity, which results in a dense composite film. Two different configurations used in the hot-press process are studied. Although there is no clear difference in the uniformity and microstructure of the composites prepared using these two configurations, the composite prepared using one configuration exhibit a higher dielectric constant with a lower loss. For the composite with 40 vol. BST, a dielectric constant of 70 with a loss of 0.07 at 1 kHz is obtained at room temperature. The composites exhibit a lower dielectric loss than the polymer matrix at high frequency. However, at low frequency, the composites exhibit a higher loss than the polymer matrix due to a low frequency relaxation process that appears in the composites. It is believed that this relaxation process is related to the interfacial layer formed between BST particle and the polymer matrix. The temperature dependence of the dielectric property of the composites was studied. It is found that the dielectric constant of these composites is almost independent of the temperature over a temperature range from 20 to 120 C. Key words: A. Polymer-matrix composites (PMCs); B. Electrical Properties; E. Casting; E. Heat treatment; Dielectric properties.

Enhanced dielectric and ferroelectric properties induced by TiO2@MWCNTs nanoparticles in flexible poly(vinylidene fluoride) composites

Abstract: Flexible polymer based composites containing multi-walled carbon nanotubes (MWCNTs) have been reported to present high dielectric constant. However, the composites generally exhibit high dielectric loss and low dielectric breakdown strength, which prohibits their practical use in electronic and electric industry. MWCNTs were coated with a continuous layer of TiO2 nanoparticles (TiO2@MWCNTs) by a simple hydrothermal process and TiO2@MWCNTs/poly(vinylidene fluoride) (PVDF) composites were prepared by a solution casting method. Compared to the pristine MWCNTs/PVDF composites, the TiO2@MWCNTs/PVDF composites presented enhanced dielectric constant and lower dielectric loss. Additionally, the breakdown strength of the TiO2@MWCNTs/PVDF composites was also improved, which is favorable for enhanced ferroelectric properties in the composites.