Springer Online Journal Archives 1860-2000
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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 ρ ≈ 103 Ω · cm) to room temperature (ρ 〉 1010 Ω · cm). An apparent dielectric constant of 〉20000 and tan δ 〈 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, α, in the range 7–12 and the varistor field, Ev, in the range 0.3–1.0 kV/cm. The value of α in the present materials increased systematically with increasing ρ in their PTCR temperature range. It has been found that there exists a close correlation between α and the grain-boundary potential barrier height, eφ, obtained from the ρ-T characteristic of the materials. An almost linear relationship was also found to exist between α and log Ev for the present materials.
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