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Synthesisand Characterization of (Bi1/2A1/2)-Modified BaTiO3(A=Na, K) Semiconducting Ceramics
Keywords: semiconducting ceramics, PTCR, electrical characterization
Barium titanate (BaTiO3; BT)-based semiconductor ceramics are widely utilized as positive temperature coefficient resistors (PTC thermistors). The PTC characteristic is associated with the ferroelectric Curie point Tc. A blending BT with lead titanate (PbTiO3) is indispensable if the device is to have a higher switching temperature than Tc of BT (= 130 oC). Recently, there is a strong demand to develop lead-free electroceramics whose properties are comparable to those of lead-contained ones. We have been proposing the semiconducting ceramics of the BaTiO3-(Bi1/2A1/2)TiO3 (A=Na, K) system as lead-free PTC thermistor materials. For determining the maximum switching temperature, the phase diagrams of the binary systems were clarified. The ceramics showed semiconductivity by sintering in N2 flow with a low O2 concentration and acquired PTC properties by the post-annealing in air. This process produced low resistivity at room temperature rather than the process by doping trivalent and pentavalent cations into Ba and Ti sites, respectively. The modified BaTiO3 semiconducting ceramics exhibit resistivity change at the temperatures up to ~210oC. Furthermore, SEM local property analysis of individual grain boundaries was carried out. Conductive mode electron beam induced current (EBIC) contrast was observed in the semiconducting ceramics as the ceramics were heated above Tc.
Hiroaki Takeda, Associate Professor
Tokyo Institute of Technology
Meguro, Tokyo 152-8552 ,
Japan


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