Nuoxin Xu

Significantly Enhanced Dielectric Performance of Poly(vinylidene fluoride-co-hexafluoropylene)-based Composites Filled with Hierarchical Flower-like TiO2 Particles

In this study, we report a feasible strategy for fabricating high-dielectric-constant polymer composites for applications in energy storage devices and embedded capacitors. Hierarchical flower-like TiO2 particles were prepared via a facile solvothermal process and incorporated into the P(VDF-HFP) matrix. The temperature and frequency dependent dielectric properties of flower-like TiO2/P(VDF-HFP) composites as well as commercial TiO2/P(VDF-HFP) composites were investigated. The results reveal that the flower-like TiO2 particles are more effective in increasing the dielectric constant of P(VDF-HFP) when compared with commercial TiO2. Typically, the dielectric constant of the P(VDF-HFP) composite filled with 20 vol % flower-like TiO2 reaches 83.1 at 100 Hz, in contrast to 43.4 for the composite filled with 20 vol % commercial TiO2 and 11.3 for pristine P(VDF-HFP). Also, the flower-like TiO2-filled composites exhibit similar characteristic breakdown strengths to their commercial TiO2-filled counterparts. The significant improvement in the dielectric constant could be attributed to the enhancement of Maxwell-Wagner-Sillars polarization, which originates from the sophisticated morphology of flower-like TiO2 particles.

Nanocomposites with BaTiO3–SrTiO3 hybrid fillers exhibiting enhanced dielectric behaviours and energy-storage densities

Herein, small loadings of SrTiO3 nanowires (ST NWs) were synthesized and grafted onto the surface of BaTiO3 nanoparticles (BT NPs) in a hydrothermal process. Nanocomposites comprised of P(VDF-HFP) matrix and ceramic fillers were prepared using BT–ST nanocrystals of different molar ratios. Microstructure and thermal analysis confirm that BT NPs have been successfully functionalized with polyphenol-Sr2+ shells on the surface, and the BT–ST-P(VDF-HFP) nanocomposites can obtain a higher thermal stability than both pure P(VDF-HFP) and BT-P(VDF-HFP) composites. Dielectric properties measured at various frequencies and temperatures indicate that the nanocomposites with several BT–ST ratios exhibit enhanced dielectric properties over a wide frequency range. With a BT–ST molar ratio of 2 and the dielectric constant of 7.5 vol% sample can increase by 3.2 and dielectric loss can decrease by 0.015, compared with BT-P(VDF-HFP) nanocomposites. In addition to the dielectric behaviours progress, the BT–ST-P(VDF-HFP) composites also possess higher electrical displacements and corresponding energy-storage densities compared to BT-P(VDF-HFP) nanocomposites. The energy density of the optimal BT–ST-P(VDF-HFP) sample is four times higher than that of pure P(VDF-HFP) under an electric field of 20 kV mm−1. All the improved performances suggest an easy method to fabricate nanocomposites bearing potential electrical applications.

High performance of P(VDF-HFP)/Ag@TiO2 hybrid films with enhanced dielectric permittivity and low dielectric loss

Ag@TiO2 core–shell nanoparticles were synthesized as fillers using a simple vapor-thermal method. Based on the nanoparticles, the P(VDF-HFP)/Ag@TiO2 hybrid films were first prepared by embedding Ag@TiO2 nanoparticles in a poly(vinylidene fluoride co-hexafluoropropylene) [P(VDF-HFP)] matrix. Microstructural and thermal analysis confirmed that Ag nanoparticles had been successfully coated by TiO2 shells and that the thickness of the shell layer was about 8–10 nm. The Ag@TiO2 nanoparticles act as nucleation sites to promote crystallization of the polymer matrix without changing its structure. The P(VDF-HFP)/Ag@TiO2 composite exhibited enhanced dielectric properties over a wide frequency range, and the dielectric permittivity of the polymer nanocomposites is enhanced by ∼300% over the P(VDF-HFP) matrix at a low filler loading of 10 vol%. Moreover, P(VDF-HFP)/Ag@TiO2 also exhibit a higher dielectric constant than P(VDF-HFP)/Ag, P(VDF-HFP)/TiO2 and P(VDF-HFP)/Ag/TiO2 blend composites while maintaining a low loss tangent (below 0.03 at 1 kHz) to achieve a duplex polarization effect.

In-situ preparation of hierarchical flower-like TiO 2 /carbon nanostructures as fillers for polymer composites with enhanced dielectric properties

Novel three-dimensional hierarchical flower-like TiO2/carbon (TiO2/C) nanostructures were in-situ synthesized via a solvothermal method involving calcination of organic precursor under inert atmosphere. The composite films comprised of P (VDF-HFP) and as-prepared hierarchical flower-like TiO2/C were fabricated by a solution casting and hot-pressing approach. The results reveal that loading the fillers with a small amount of carbon is an effective way to improve the dielectric constant and suppress the dielectric loss. In addition, TiO2/C particles with higher carbon contents exhibit superiority in promoting the dielectric constants of composites when compared with their noncarbon counterparts. For instance, the highest dielectric constant (330.6) of the TiO2/C composites is 10 times over that of noncarbon-TiO2-filled ones at the same filler volume fraction, and 32 times over that of pristine P (VDF-HFP). The enhancement in the dielectric constant can be attributed to the formation of a large network, which is composed of local micro-capacitors with carbon particles as electrodes and TiO2 as the dielectric in between.

Phase transition and piezoelectric properties of alkali niobate ceramics through composition tuning

(1 − x)(K0.40Na0.60)(Nb0.95Sb0.05)O3–x(Bi0.5K0.5)HfO3 lead-free piezoceramics were prepared by conventional sintering method, and effects of BKH on phase transition and piezoelectric properties of the ceramics are systematically investigated. XRD as well as TEM analysis indicates rhombohedral, orthorhombic and tetragonal phase coexistence for 0.03 ≤ x ≤ 0.05 and greatly enhanced piezoelectric properties are observed in the ceramics with mixed phase coexistence regime, i.e., d*33 (∼614 pm V−1) and d33 (∼400 pC N−1) for x = 0.035. The results show that KNNS–xBKH ceramics have potential to partially substitute PZT, and demonstrate polymorphic phase boundary (PPB) involving R phase induced by composition tuning is mostly contributed to remarkably enhanced properties of KNN-based ceramics because of lower anisotropic energy than in O–T phase coexistence PPB.

TiO2@Ag/P (VDF-HFP) composite with enhanced dielectric permittivity and rather low dielectric loss

Ag-loaded TiO2 hybrid particles (TiO2@Ag) were synthesized as fillers by using an ethylene glycol reduction method. Based on this, the TiO2@Ag/P(VDF-HFP) hybrid films were prepared by embedding TiO2 nanoparticles in a poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] matrix. Morphology and thermal analysis show that the introduction of TiO2@Ag does not disrupt the continuity of the polymer matrix, while the strong interaction between fillers and matrix influences the crystallization process of the composite. The adhesion of Ag to TiO2 efficiently separates the Ag particles from connecting and suppresses the formation of a conductive network, and the ultra-small Ag nanoparticles “trap” the carriers due to coulombic blockade and quantum confinement effect, which results in low dielectric loss and electrical conductivity of the composites. As a consequence, the dielectric permittivity of polymer nanocomposites was enhanced by 300% over the P(VDF-HFP) matrix at a filler content of 30 vol% while maintaining a rather low dielectric loss (0.037 at 1 kHz), demonstrating promising applications in electronic devices.