PTCR ceramics of (Ba0.998Sm0.002)TiO3 + 0.001MnCO3 + xSiO2 (x=1, 2, 3, 4, 5, 6 mol%) were fabricated by solid state method. Disk samples of diameter 5 mm and thickness about 1mm were sintered at 1,290℃ for 2 h in reduced atmosphere of 5%H2-95%N2 followed by re-oxidation at 600℃ for 30 min. in 20%O2-80%N2.and their microstructures and electrical properties were investigated with SEM and Multimeter. The color of sintered samples was strongly dependent on SiO2 content showing that the color of samples with SiO2 of 1∼2 mol% was gray but that of samples with SiO2 of 4∼6 mol% was changed from gray to blue, which seems to be related with the reduction of samples due to the oxygen vacancies created during the sintering in reduced atmosphere. SiO2 content had a great influence on the microstructure and the electrical properties. With increasing SiO2 content, the grain size of samples increased and the resistivity as well as the resistivity jump (R285/Rmin) decreased, which is considered to be attributed to the resistivity change at grain interior and grain boundary due to the fast mass transfer through SiO2 liquide phase during the sintering. Samples with 2 mol% SiO2 has the resistivity of 202 Ω cm and the resistivity jump of 3.28. It is expected that SiO2 doped BaTiO3 based PTC ceramics can be used for multilayered PTC thermistor due to the resistance to the sintering in reduced atmosphere.
