Influence of BaTi Ratio on the Positive Temperature Coefficient of Resistivity Characteristics of Ca-Doped Semiconducting BaTiO sub(3) Fired in Reducing Atmosphere and Reoxidized in Air

The positive temperature coefficient of resistivity (PTCR) characteristics of donor-doped BaTiO sub(3) fired in a reducing atmosphere and reoxidized in air are investigated. The result reveals that conventional semiconducting BaTiO sub(3) ceramics fired in a reducing atmosphere and reoxidized at a low temperature of 800C in air show minimal PTCR characteristics, as reported earlier; however, Ca-doped BaTiO sub(3) with compositions in the range of 1.005,(Ba+Ca+La)Ti,1.010 exhibit pronounced PTCR characteristics, even when reoxidized at such a low temperature. The semiconducting BaTiO sub(3) ceramics with {(Ba+Ca+La)Ti}=1.005 and Ca-doped to 20 mol% exhibit remarkable PTCR characteristics with a resistivity jump of two orders of magnitude when they have been reoxidized at 800C after firing in a reducing atmosphere.