Characteristics of porous BaTiO3-based PTC thermistors fabricated by adding graphite powders

The crystalline structure, microstructure, and electrical properties of porous graphite-containing BaTiO3-based PTC thermistors were studied. The sintered ceramics showed a tetragonal perovskite structure, irrespective of the added graphite content. The added graphite formed the interstitial solid solutions with Ba0.999Sb0.001TiO3 and was distributed homogeneously in the sintered ceramics. The grain size of the as-sintered graphite-containing BaTiO3-based ceramics was much larger than that of the as-sintered graphite-free ones. This is mainly due to the exothermic reactions of the graphites and oxygen molecules in the ceramics. The porosity of the as-sintered ceramics increased with increasing graphite content due to an enhanced evolution of CO and CO2 gases associated with the exothermic reactions. It was found that the newly prepared porous graphite-containing BaTiO3-based PTC thermistors showed a large PTCR effect. (C) 2003 Ellsevier B.V. All rights reserved.