Fabrication And Dielectric Properties Of Niobate/Poly(Vinylidene Fluoride) Composites Films

With the development of high-technology, the traditional single phase materials have been difficult to meet the requirements of application, especially in the field of capacitors and high energy storage devices. Ceramic/polymer composites integrate the advantages of the two phases which were the good dielectric properties of ceramic materials and the good mechanical strength and processing performance of polymer materials. One of the key problem was the selection of inorganic fillers. Inorganic high dielectric fillers were widely used in the preparation of inorganic/polymer composite, such as BaTiO3(BT), Pb(Zr, Ti)O3(PZT), and Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) and other ferroelectric ceramic particles. Recently, KxNa1-xNbO3(KNN) was widely researched as a kind of lead-free ceramics, due to its excellent ferroelectric and piezoelectric properties as well as friendly to the environment. In addition, solid solution of ferroelectric materials KNN, in the field of high frequency applications, was selected with a high dielectric constant, low dielectric loss, and low aging rate and plane coupling coefficient in wide frequency range.In this paper, KNN fillers were prepared by a traditional solid-state reaction. Then the morphology and composition of KNN particles were characterized by SEM and EDS, respectively. KNN particles size is about 1 microns. And the ratio of K and Na is 1:1 in KNN particles, which indicates the successful preparation of K0.5Na0.5NbO3 ceramic powder. In this paper, KNN/PVDF hybrid films with high dielectric permittivity were prepared by a solution casting process. The structure, morphology and dielectric properties of the KNN/PVDF films were characterized and analyzed through the measurements of FT-IR, XRD, SEM and dielectric. The effects of the doping KNN particles, well dispersed in the matrix, on the structure, morphology, and dielectric properties of KNN/PVDF hybrid films were investigated. The introduction of KNN fillers has a remarkable influence on the α-, β-, γ-phase structure and the crystallinity of the polymer matrix; and it is also effective in improving the dielectric performance. A dielectric permittivity as high as 250 is obtained at 10 Hz when the concentration of the KNN filler reaches 30 vol.%, which is 28 times higher than that of the pure PVDF matrix. The conductivity of the hybrid film with 40 vol.% KNN concentrations is lower than 8×10-10(S cm-1) at 102 Hz and room temperature, which shows the excellent insulation and is important for the potential application of this kind of KNN/PVDF hybrid films in future electronic industry.