Influence of Excessive SiO_2 or TiO_2 on the Electric Properties of Ba_(0.92)Ca_(0.08)TiO_3 PTCR Ceramics

The dependence of electrical properties of Ba0.92Ca0.08TiO3 PTC ceramics on the SYO2 or TiO2 content was studied. The dependence of room, temperature resistivity on the SiO2 content was determined by the variation of the microstructure of Ba0.92Ca0.08TiO3 PTC ceramics . It was shown that a small amount of excessive TiO2 (2mol% ) added could increase the dielectric constant of materials, and it results in a reducing of the potential height (e·) of grain boundary. Thus, samples with particularly low room temperature resistivity were obtained. The relationship of PTC effect with the TiO2 content was also discussed by using the chemistry defect theory . The inferior PTC effect caused by excessive TiO2 may be concerned with the behavior of oxygen vacancies in the grains of ceramics.