Dielectric Properties of Ba 0.5 Sr 0.5 TiO 3 -P(VDF-CTFE) Nanocomposites
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Dielectric Properties of Ba0.5Sr0.5TiO3-P(VDF-CTFE) Nanocomposites Pei-xuan Wu, Xiaobing Shan, and Zhong-yang Cheng Materials Research and Education Center, Auburn University, Auburn, AL, 36849 ABSTRACT Ceramic/polymer composite made of nanosize Ba0.5Sr0.5TiO3 (BST) powders and P(VDF-CTFE) copolymers as matrix. The concentration of the composites with BST from 0% to 40% in volume was investigated. The dielectric properties and structure as well as the morphology of the composites were characterized over a broad temperature range. It is found that the wetability between the polymer and ceramic powder is poor. The approach to improve the uniformity of composites was investigated. Due to the dielectric-constant-maximum temperature of the BST is different from that of copolymer, a weak dependence of the dielectric constant on temperature was observed over temperature from 10 °C to 100 °C. INTRODUCTION Polymers, as a kind of dielectric materials, are currently the suitable material chosen for actuators, energy storage devices because of their high energy density and low dielectric loss, such as poly(vinylidene fluoride)-co-chlorotrifluoroethylene [P(VDF-CTFE)] [1]. However, for the polymers with high dielectric strength and high flexibility, its dielectric constant is low (around 2~3). Consequently, a ceramic/polymer composite is in need of possessing both high dielectric constant and high flexibility properties. To obtain this goal, the ferroelectric ceramics have been chosen and the dielectric properties of composite have been improved. A dielectric constant of 13.9 with a loss of 0.014 was got at 0.1 MHz in BaSrTiO3 (BST) and thermoplastic cyclic olefin copolymer (COC) [2]. And it was reported that the nanosize ceramic powders of 0-3 type composites could increase the microstructure of the composite [3]. The main purposes of this experiment were to prepare a 0-3 type ceramic–polymer composite made of P(VDF-CTFE) with different concentrations of ferroelectric barium strontium titanate Ba0.5Sr0.5TiO3 (BST) nanosize powders and study the dielectric properties of the nanocomposite. EXPERIMENT In this experiment, P(VDF-CTFE) copolymer, with VDF/CTFE ratio 88/12 mol% was chosen for matrix and Ba0.5Sr0.5TiO3 (BST, from nGimat Co.) naonpowder as filler. The BST/P(VDF-CTFE) composite films were prepared by solution-cast method. P(VDF-CTFE) 88/12 mol% copolymer was dissolved in N, N dimethylformamide (DMF) with magnetic stirring for 4 hours. After the BST powder added into the solution, it was stirred for 8 hours. The solution was cast on glass substrate and dried at 70 °C for 8 hours in an oven. Then the thin film was annealed at 140oC for 2 hours. In order to improve the wettability, a hot compression technique was used. Gold electrodes were sputtered on both sides of the thin film samples (single layer & hot compressed multilayer). Agilent 4294A impedance analyzer was used to measure the dielectric property of the samples. The measured frequency range is 100 Hz to 10 MHz. JEOL
(JSM-7000F) Field Emission Scanni
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