Dielectric constant and energy density of poly(vinylidene fluoride) nanocomposites filled with core-shell structured BaTiO3@Al2O3 nanoparticles

doi:10.1016/j.ceramint.2016.11.128

Ceramics International

Volume 43, Issue 3, 15 February 2017, Pages 3127-3132

https://doi.org/10.1016/j.ceramint.2016.11.128 Get rights and content

Abstract

Ceramics-polymer nanocomposites consisting of core-shell structured BaTiO₃@Al₂O₃ (BT@Al₂O₃) nanoparticles as the filler and poly(vinylidene fluoride) (PVDF) as the polymer matrix were fabricated by solution casting. At the same volume fraction, the BT@Al₂O₃/PVDF nanocomposites, with larger dielectric constant and higher energy density, outperformed the BT/PVDF nanocomposites. The 2.5 vol% BT@Al₂O₃/PVDF nanocomposites at 360 MV/m had a double more energy density than pure PVDF at 400 MV/m (6.19 vs. 2.30 J/cm³), and a remarkably 42% lower remnant polarization than the 2.5 vol% BT/PVDF nanocomposites (0.99 vs. 1.69 μC/cm² at 300 MV/m). Such significant enhancement was closely related to the surface modification by Al₂O₃, which improved the insulation of BT nanoparticles and reduced the contrast of dielectric constant between the filler and the PVDF matrix.

Introduction

Ceramics-polymer nanocomposites have attracted wide attention in the past decade due to their potential for high-energy storage applications [1], [2], [3], [4], [5]. These nanocomposites can be broadly applied in electrical and electronic fields (e.g. embedded capacitors, high charge-storage capacitors, and memory devices) owing to the combination of large dielectric constant from the ceramic fillers and high breakdown strength and mechanical flexibility from the polymer matrix [6], [7], [8]. The energy storage density of dielectric materials is defined by the integral U=∫EdP (where E is the applied electric field and P is the polarization) implies that the high energy storage density strongly depends on a large dielectric constant and high breakdown strength. At present, the main focus is to enhance the dielectric constant of nanocomposites by incorporating large-dielectric-constant conductive fillers or ceramic fillers. As reported, the 20 vol% Ag nanowires embedded into a PVDF matrix improved the dielectric constant at 100 Hz to 800, and remained at 379 up to 1000 Hz [9]. As the load of BaTiO₃ particles as a dopant into a polyimide matrix rose from 0 to 67.5 vol%, the dielectric constant of the films increased from 3.53 to 46.50 [10].

The filler-matrix interface is critical in determining the energy storage density of nanocomposites [11], [12], [13]. On one hand, the incorporation of conductive or ceramic fillers results in the agglomeration of fillers, air voids, inorganic-organic interfaces and other defects, increasing the leakage current and decreasing the breakdown strength of the nanocomposites [14]. On the other hand, the contrast of dielectric constants between fillers and matrix produces an inhomogeneous local electric field, which further declines the breakdown strength [15]. Therefore, to synthesize homogeneous nanocomposites, some researchers aim to reduce the negative influences due to the incorporation of ceramic fillers. For instance, Ba_0.3Sr_0.7TiO₃ nanofibers prepared via electrospinning were modified by dopamine and evenly dispersed in the poly(vinylidene fluoride-trifluoroethylene) matrix [16]. SiO₂-layer-coated BaTiO₃ nanoparticles were homogeneously distributed in PVDF, and the energy density was increased to 6.28 J/cm³ by a load of 2 vol% SiO₂-layer-coated BaTiO₃ nanoparticles [17].

Here we report an approach to synthesize core-shell structured BT@Al₂O₃ through precipitation. Homogeneous nanocomposites were prepared starting from core-shell structured BT@Al₂O₃ nanoparticles as the filler and PVDF as the matrix. Dielectric responses and energy storage properties of the nanocomposites were studied.

Section snippets

Experimental

Substances used here included BaTiO₃ nanoparticles (diameter 100 nm, Guoteng Co. Ltd, China), PVDF (3F New Materials Co. Ltd, China), ammonia, aluminum sulfate (Al₂(SO₄)₃), N,N-dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) (Sinopharm Chemical Reagent Co. Ltd, China).

The Al₂O₃ layer was synthesized through the precipitation reaction of Al₂(SO₄)₃ on the surface of BT nanoparticles. The BT nanoparticles were dispersed in an aqueous PVP solution and then ultrasonicated for 1 h. Then the

Results and discussion

Al₂O₃ layers were continuously coated onto the surfaces of BT nanoparticles, as evidenced by the HRTEM of the core-shell structure (Fig. 1a). The amorphous layers are about 5 nm thick. As showed in Fig. 1b, the XRD patterns of the BT@Al₂O₃ nanoparticles and untreated BT particles both show the pure tetragonal phase, without obvious change in the crystal structures. These results indicate that Al₂O₃ existed as an amorphous structure.

The amorphous layers were further verified as Al₂O₃ layers by

Conclusions

Core-shell structured BT@Al₂O₃ nanoparticles were prepared by the precipitation method, and then combined with PVDF to synthesize high-energy-density nanocomposites through a solution casting method. TEM and XPS reveal that Al₂O₃ was continuously coated atop the BT nanoparticles with an average thickness of 5 nm. The BT@Al₂O₃/PVDF nanocomposites exhibited much higher energy discharge and much lower energy loss than the BT/PVDF nanocomposites, which was because the Al₂O₃ layer enhanced the

Acknowledgment

This work was supported by the Ministry of Science and Technology of China, China through 973-project (Grant no.2015CB654601). International Science and Technology Cooperation Program of China, China (Grant no. 2013DFR50470) and National Natural Science Foundation of China (Grant no.51272177).

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Dielectric constant and energy density of poly(vinylidene fluoride) nanocomposites filled with core-shell structured BaTiO3@Al2O3 nanoparticles

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgment

Compos. Part A: Appl. Sci. Manuf.

Ceram. Int.

Ceram. Int.

Ceram. Int.

Ceram. Int.

Ceram. Int.

Ceram. Int.

J. Colloid Interface Sci.

Ultrahigh energy density of polymer nanocomposites containing BaTiO3@TiO2 nanofibers by atomic-scale interface engineering

Adv. Mater.

Phosphonic acid-modified barium titanate polymer nanocomposites with high permittivity and dielectric strength

Adv. Mater.

Ultra high energy density nanocomposite capacitors with fast discharge using Ba0.2Sr0.8TiO3 nanowires

Nano Lett.

Fabrication of novel Ag nanowires/poly(vinylidene fluoride) nanocomposite film with high dielectric constant

Phys. Status Solidi A

Dielectric constant and energy density of poly(vinylidene fluoride) nanocomposites filled with core-shell structured BaTiO₃@Al₂O₃ nanoparticles

Ultrahigh energy density of polymer nanocomposites containing BaTiO₃@TiO₂ nanofibers by atomic-scale interface engineering

Ultra high energy density nanocomposite capacitors with fast discharge using Ba_0.2Sr_0.8TiO₃ nanowires