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Microscopic Mechanism of measures by the impurity ( niobium , manganese ) co-doped BaTiO_3 ceramic PTC effect

Author: FangLiMin
Tutor: YangHai
School: Yunnan Normal University
Course: Astrophysics
Keywords: Microwave sintering Barium titanate ceramics PTC effect Ferroelectric polarization Curie-Weiss law
CLC: TQ174
Type: Master's thesis
Year: 2006
Downloads: 208
Quote: 0
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Abstract


Barium titanate （BaTiO3） is a dielectric material, with a perovskite （ABO3） structure that finds many applications in electronic devices. When pure, this material is highly resistive at room temperature but its electrical resistivity can be dramatically lowered by some dopants. Suitably doped, semiconducting barium titanate polycrystals or ceramics exhibit an anomalous electrical resistivity increase above the Curie temperature Tc. This increase is well known as the positive temperaturecoefficient of resistivity （PTCR） effect, and has been utilized as PTC thermistors. The fundamental physical explanations for these intriguing characteristics have attracted a considerable amount of research.In this paper, at first, we review the research survey of the microwave sintering technology and the developments of PTCR ceramics, in which we expatiate on the main characters of the microwave sintering technology and the progresses of its applications both here and abroad; the properties, applications, classifications of PTCR ceramics; the mechanism of the microwave sintering technology and theoretical models of the PTC effect of the composites based on BaTiO3. Secondly, by comparing the sintering time, grain size, relative density of the microwave sintering ceramics to the traditional sintering method, we educe that the main characters of the microwave sintering are simple, fast, energy efficient, especially which can restrain the grain growth and make the tenacity and ductibility of grains better. Thirdly, we analyze the relations between the Jahn-Teller effect and the structural phase transition of BaTiO3 ceramics, and make it simple the complicated phase transition from paraelectric state to ferroelectric state. At last, we investigate the mechanism of the PTC effect of BaTiO3 ceramics doped donor dopants （Nb） and acceptor dopants （Mn） simultaneously through the analysis of electrical resistivity as a function of temperature and XRD of samples. So we conclude that it’s a good explanation of the PTC effect with Heywang model and the effect of spontaneous polarization. Moreover, we present some feasible aspects of the research on the BaTiO3 ceramics in

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