Varistor characteristics in PTCR-type (Ba,Sr)TiO3 ceramics prepared by single-step firing in air.

This paper deals with donor, acceptor-codoped (Ba_0.4Sr_.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, E_v, 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 E_v for the present materials. [ABSTRACT FROM AUTHOR]