Varistor characteristics in PTCR-type (Ba,Sr)TiO3 ceramics prepared by single-step firing in air |
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Authors: | M Kuwabara H Matsuda Y Ohba |
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Affiliation: | (1) Department of Materials Science, The University of Tokyo, 7-3-1 Hongo, Tokyo, 113, Japan;(2) Taiko Refractories Co., Kitakyushu, 804, Japan |
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Abstract: | This paper deals with donor, acceptor-codoped (Ba0.4Sr.6)TiO3 ceramics with distinct varistor characteristics at room temperature, which were prepared by single-step firing in air. The materials, with the Curie point at around –90 °C, exhibited a large PTCR (positive temperature coefficient of resistivity) effect of more than seven orders of magnitude in the temperature range –90 °C (the resistivity 103 · cm) to room temperature ( > 1010 · cm). An apparent dielectric constant of >20000 and tan < 0.05 (at 100 kHz) were observed for the present materials at room temperature, and moreover, the materials exhibited nonlinear current-voltage characteristics with the nonlinear coefficient, , in the range 7–12 and the varistor field, Ev, in the range 0.3–1.0 kV/cm. The value of in the present materials increased systematically with increasing in their PTCR temperature range. It has been found that there exists a close correlation between and the grain-boundary potential barrier height, e , obtained from the -T characteristic of the materials. An almost linear relationship was also found to exist between and log Ev for the present materials. |
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