Carbon black (0 to 60 vol%) was added to (Ba,Sr)TiO3 powder. The resulting mixture was treated by sonication and freeze drying. The effects of the carbon black content on the microstructure and PTCR characteristics of the resulting porous (Ba,Sr)TiO3 ceramics were investigated. The combined process of sonication and freeze drying was an effective method for preparing a homogeneous dispersion of nano-size carbon black. The porosities of all (Ba,Sr)TiO3 ceramics were < 10%. The PTCR jump of the (Ba,Sr)TiO3 ceramics prepared with carbon black was > 106, and increased slightly with increasing carbon black content. Carbon black is an effective additive for BaTiO3-based ceramics, showing excellent PTCR characteristics. The change in the resistivity of porous (Ba,Sr)TiO3 ceramics can be explained in terms of the change in potential barrier height due to the chemisorption/desorption of oxygen atoms at the grain boundaries.

Keywords: Carbon black, Freeze drying, Y-doped (Ba,Sr)TiO3 ceramics, PTCR