Microstructure and dielectric behavior of the three-phase Ag@SiO 2 /BaTiO 3 /PVDF composites with high permittivity
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Shuhui Yu,a) Rong Sun,b) and Suibin Luo The Chinese University of Hong Kong, Shatin, N.T. Hong Kong 999077, China
Xianwen Liang, Jie Wan, and Zhiqiang Zhuang Department of Materials Science and Engineering, South China University of Technology, Tianhe District, Guangzhou 510641, China (Received 9 May 2011; accepted 9 December 2011)
Ag nanoparticles were prepared via a wet chemical reduction method and treated with tetraethoxysilane (TEOS) to form an insulating SiO2 layer on the surface (Ag@SiO2). The Ag@SiO2 nanoparticles were introduced in to the BaTiO3/poly (vinylidene fluoride) matrix to prepare the three-phase Ag@SiO2/BaTiO3/poly (vinylidene fluoride) composite, and the dielectric behavior of the composite was investigated. The results showed that the typical “conductor/ polymer” percolation effect was not observed in the composite as a result of the SiO2 layer, which prevented Ag particles from contacting with each other directly and restricted the movement of electrons under external field. The high dielectric constant of 723 and a relatively low loss of 0.82 were achieved at 100 Hz with 40 vol% Ag@SiO2 and 20 vol% BaTiO3, respectively. The microcapacitor network model and “Maxwell-Wagner-Sillars” (MWS) effect were used to investigate dielectric properties of the three-phase composite.
I. INTRODUCTION
Recently, much work has been devoted to developing conductor/polymer composites with high dielectric constant, in which an “insulator/conductor” transition has been demonstrated, which is called the percolation effect. In this type of composites, dielectric constant (k) of the composites climbs up abruptly as the concentration of the conducting fillers approaches the neighborhood of the percolation threshold.1–4 The dielectric constant of these composites is much higher than the widely used ceramic/ polymer composites. However, the high loss (tand) in these conductor/polymer composites, which is caused by the percolation tunneling current, weakens their dielectric performance. Li et al.5 reported that the poly (vinylidene fluoride) (PVDF) composite containing 4 vol% ester functionalized multiwall carbon nanotube (MWCNT), exhibited a dielectric constant of 400 at 1 kHz. However, its loss tangent was close to 10. An effective way to reduce dielectric loss of the conductor/polymer composite is coating the conducting particles with a thin insulating layer to form the core@shell structure. For instance, Shen has prepared Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2012.26 J. Mater. Res., Vol. 27, No. 7, Apr 14, 2012
Ag@C composite particles via carbonaceous shell coating on the Ag surface. The dielectric loss of Ag@C/ epoxy composite showed a low value of 0.05 at 1 kHz.6 Besides, as demonstrated by Xu, a low dielectric loss of 0.02 in Al@Al2O3/epoxy composites was achieved.7 SiO2 thin film is a commonly used insulating material with good stability. The SiO2 layer can be formed by hydrolyzing tetraethoxysilane (TEOS) on the surface of metal pa
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