Effect of atmosphere on the PTCR characteristics of porous (Ba,Sr)TiO3 ceramics

Porous and fine-grained (Ba,Sr)TiO3 ceramics were fabricated by adding partially oxidized Ti powders. During heating and cooling, the electrical resistance was measured in air, O2, N2, and H2 atmospheres and in H2 followed by air atmosphere. The effect of atmosphere on the PTCR characteristics and the role of oxygen on the grain-boundaries in the PTCR characteristics were investigated. The porous (Ba,Sr)TiO3 ceramics showed a large PTCR effect, which was strongly sensitive to atmosphere. This effect was increased in oxidizing atmosphere mainly because of an increase in potential barrier height whereas decreased in reducing atmosphere mainly because of a decrease in potential barrier height.