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The Study of Dielectric Properties of BatiO3/Cu Ceramic Composites

Author: XuNing
Tutor: PuYongPing
School: Shaanxi University of Science and Technology
Course: Materials Science and Engineering
Keywords: ceramic/metal composites percolation theory dielectricproperties
CLC: TB332
Type: Master's thesis
Year: 2012
Downloads: 81
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The incessant development of the electronic technique calls for electroniccomponents with micromation, high-stored energy, multifunction andintelligence. To meet the demand, the dielectric materials in the electroniccomponents like capacitors must have good performance on dielectric constantand dielectric properties by optimizing technics and formula. Nowadays, theceramic capacitors use the perovskite structure dielectric materials with higherdielectric constant, while dielectric constant of single-phase materials is limited.Composites which have higher dielectric constant seems to be an excellentsubstitute. At the same time, the percolation theory used to describeheterogeneous composite system in a phase of long-range coupling provides agood theoretical guidance to research and develop the high dielectric constantcomposite materials.This paper based on the percolation theory studied dielectric properties ofthe Barium Titanate and copper ceramic composite with high dielectric constants.BaTiO3/Cu ceramic composites were fabricated by the traditional mixing methodin nitrogen gas. The phase and microstructure of the obtained ceramiccomposites were investigated using X-ray diffraction, SEM and EDS, while themechanical properties and electric properties of the composites were measuredby a three bending test and impedance spectroscopy respectively.1. From the XRD patterns of the BaTiO3/Cu ceramic composites sintered innitrogen gas with traditional solid phase sintering method, the diffraction peaksof the composites which has no shift changes in accord with pure BaTiO3and Cu.Besides that, the peak value of Cu increases with increasing its content and noother phase were observed. All leads to a conclusion that no reaction took placebetween BaTiO3and Cu during the sintering and the copper was not incorporatedinto the perovskite structure of BaTiO3.2. The mechanical behavior of the composites improves obviously with adding Cu into BaTiO3matrix. The bending strength of the composites had aabrupt change to134.4MPa,1.6times larger than that of the monolithic BaTiO3when adding the Cu content to30wt.%. It can be explained,on the one hand,with the introduction of metal particles into a matrix of BaTiO3, the energyreleased from the crack propagation was absorbed by the plastic deformation ofthe metal and stopped the formation of the micro-cracks at the phase boundary.On the other hand, the interface between BaTiO3and Cu gives an opportunity todevelop an interpenetrating network with a strong ceramic-metal bonding, thusincreasing the bending strength of the matrix greatly.3. The electric properties of the BaTiO3/Cu ceramic composites exhibit anonlinear translated with increasing Cu content, and the percolation threshold ofthe composites is25wt.%. The copper particles randomly dispersed in BaTiO3matrix when copper content was below the percolation threshold lead to a verylow composite conductivity, close to that of the BaTiO3. When copper contentincreased to the percolation threshold, the conductivity of the composites took anonlinear translation and became close to that of the conductive phase4. According to the percolation theory, dielectric constant of the BaTiO3/Cuceramic composites increased to1.0×105at1kHz, which can be explained bythe space charge polarization, result of the accumulated charge between theinterface of two phase with different conductivity, which also could be refered asMaxwell-Wagner polarization model. With the frequency went higher to about1kHz, the conductivity took a nonlinear decrease

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