Effects of Ba/Ti Ratio on Positive Temperature Coefficient of Resistivity Characteristics of Donor-doped BaTiO3 Fired in Reducing Atmosphere

The positive temperature coefficient (PTC) of resistivity characteristics of donor-doped BaTiO3 fired at 1350 °C in a reducing atmosphere of 1×10-7 MPa at the partial pressure of oxygen is investigated. The result reveals that BaTiO3 ceramics fired in such a reducing atmosphere usually exhibit low PTC characteristics, whereas La-doped BaTiO3 with compositions in the range of (Ba+La)/Ti≧1.02 exhibit pronounced PTC characteristics. A La content of less than 0.4 mol % is suitable for the PTC characteristics, while samples doped with more than 0.8 mol % La do not show the PTC characteristics. The PTC characteristics of semiconducting BaTiO3 fired in a reducing atmosphere are enhanced with a decrease in the ion radius of a donor ion in the order La