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Dielectric polymer composites with high dielectric constants and high thermal conductivity have many potential applications in modern electronic and electrical industry. In this study, three-phase composites comprising poly(vinylidene fluoride) (PVDF), barium titanate (BT) nanoparticles, and β-silicon carbide (β-SiC) whiskers were prepared. The superiority of this method is that, when compared with the two-phase PVDF/BT composites, three-phase composites not only show significantly increased dielectric constants but also have higher thermal conductivity. Our results show that the addition of 17.5 vol % β-SiC whiskers increases the dielectric constants of PVDF/BT nanocomposites from 39 to 325 at 1000 Hz, while the addition of 20.0 vol % β-SiC whiskers increases the thermal conductivity of PVDF/BT nanocomposites from 1.05 to 1.68 W m(-1) K(-1) at 25 °C. PVDF/β-SiC composites were also prepared for comparative research. It was found that PVDF/BT/β-SiC composites show much higher dielectric constants in comparison with the PVDF/β-SiC composites within 17.5 vol % β-SiC. The PVDF/β-SiC composites show dielectric constants comparable to those of the three-phase composites only when the β-SiC volume fraction is 20.0%, whereas the dielectric loss of the PVDF/β-SiC composites was much higher than that of the three-phase composites. The frequency dependence of the dielectric property for the composites was investigated by using broad-band (10(-2)-10(6) Hz) dielectric spectroscopy.

Barium titanate/polyimide (BaTiO3/PI) nanocomposite films with high dielectric permittivity (20), high breakdown strength (67 MV m−1), and high thermal stability are prepared by an in‐situ polymerization process. A very thin polymer layer (about 5 nm) is coated on the surface of nanosized BaTiO3 particles to form a core–shell‐like structure, which can guarantee homogeneous dispersion of the BaTiO3 particles in the PI matrix. It is confirmed that the core–shell‐like structure originates from both the electrostatic attraction between the precursor poly(amic acid) (PAA) and the BaTiO3 particles and the hydrogen bond interaction between PI and the BaTiO3 particles. Such a structure also has some influence on the dielectric properties and breakdown strength of films. After casting and degassing of the sticky film, the dielectric permittivity of the nanocomposite film is close to or even higher than that of submicrocomposite films, which is attributed to the advanced interfacial structure between the BaTiO3 and PI phases.

Nanodielectrics, which are concentrated in polymer matrix incorporating nanofillers, have received considerable attention due to their potential benefits as dielectrics. In this paper, short-term breakdown and long-term failure properties of nanodielectrics have been reviewed. The characteristics of polymer matrix, types of nanoparticle and its content, and waveforms of the applied voltage are fully evaluated. In order to effectively comment on the published experimental data, a ratio k has been proposed to compare the electric properties of the nanodielectrics with the matrix and assess the effect for nanoparticles doping. There is evidence that the short-term breakdown properties of nanodielectrics show a strong dependence on the applied voltage waveforms. The polarity and the cohesive energy density (CED) of polymer matrix have a dramatic influence on the properties of nanodielectrics. Nanoparticle doped composites show a positive effect on the long-term failure properties, such as ageing resistance and partial discharge (PD) properties of nanocomposites are superior than microcomposites and the matrix. The larger the dielectric constant and CED of the matrix become, the more significant improvements in long-term performance appear. Based on the reported experimental results, we also present our understandings and propose some suggestions for further work.

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The incorporation of graphene sheets (GSs) into polymer matrices affords engineers an opportunity to synthesize polymer composites with excellent physical performances. However, the development of high performance GS-based composites is difficult because of the easy aggregation of GSs in a polymer matrix as well as the weak interfacial adhesion between GSs and the host polymer. Herein, we present a simple and effective route to hyperbranched aromatic polyamide functionalized graphene sheets (GS-HBA). The resulting GS-HBA exhibits uniform dispersion in a thermoplastic polyurethane (TPU) matrix and strong adhesion with the matrix by hydrogen-bond coupling, which improve the load transfer efficiency from the matrix to the GSs. Thus, the GS-HBA-TPU composites possess excellent mechanical performance and high dielectric performance. It has been demonstrated that the GS-HBA composite has higher modulus, higher tensile strength and higher yield strength, and remains at nearly the same strain at break when compared with the composites with graphene oxide, ethylene diaminemodified graphene, and hydrazine reduced graphene. In addition, the hyperbranched polymer chains allow construction of a large number of microcapacitors and suppress the leakage current by isolating the GSs in a TPU matrix, resulting in a higher permittivity and lower loss tangent for the GS-HBA composite in comparison with ethylene diamine-modified graphene, or hydrazine reduced-graphene composites.

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Acceptor doping and donor doping have been known to result in opposite ferroelectric aging effects, but the aging effect of hybrid-doped (acceptor+donor) ferroelectrics has remained unclear. In this letter the authors report the aging effect in Mn3++Nb5+ hybrid-doped BaTiO3 ceramics with acceptor fixed at 1mol% but with donor varied from 0.5to2mol%. The authors found surprisingly that ferroelectric aging existed in all the samples, no matter which of the two, acceptor or donor, was dominant: all the samples showed a double hysteresis loop after aging, but with increasing donor (Nb5+) concentration the coercive field and hysteresis decrease. Meanwhile, a large nonlinear recoverable electrostrain up to 0.17% (due to reversible domain switching) was observed at 3kV∕mm, which exceeded that of acceptor-monodoped ceramics and was about twice the piezoelectric strain of hard lead zirconate titanate. These results demonstrate that hybrid doping is an effective way to enhance the domain-switching-related electrostrain properties. Finally, the aging effect of hybrid-doped ferroelectrics was explained.