BaTiO3PTC 써미스터의 미세구조 및 전기적 특성에 대한 SiO2영향

Abstract

PTCR ceramics of <TEX>$(Ba_{0.998}Sm_{0.002})TiO_3+0.001MnCO_3+xSiO_2$</TEX> (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 <TEX>$1,290^{\circ}C$</TEX> for 2 h in reduced atmosphere of <TEX>$5%H_2-95%N_2$</TEX> followed by re-oxidation at <TEX>$600^{\circ}C$</TEX> for 30 min. in <TEX>$20%O_2-80%N_2$</TEX>.and their microstructures and electrical properties were investigated with SEM and Multimeter. The color of sintered samples was strongly dependent on <TEX>$SiO_2$</TEX> content showing that the color of samples with <TEX>$SiO_2$</TEX> of 1~2 mol% was gray but that of samples with <TEX>$SiO_2$</TEX> 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. <TEX>$SiO_2$</TEX> content had a great influence on the microstructure and the electrical properties. With increasing <TEX>$SiO_2$</TEX> content, the grain size of samples increased and the resistivity as well as the resistivity jump (<TEX>$R_{285}/R_{min}$</TEX>) decreased, which is considered to be attributed to the resistivity change at grain interior and grain boundary due to the fast mass transfer through <TEX>$SiO_2$</TEX> liquide phase during the sintering. Samples with 2 mol% <TEX>$SiO_2$</TEX> has the resistivity of <TEX>$202{\Omega}cm$</TEX> and the resistivity jump of 3.28. It is expected that <TEX>$SiO_2$</TEX> doped <TEX>$BaTiO_3$</TEX> based PTC ceramics can be used for multilayered PTC thermistor due to the resistance to the sintering in reduced atmosphere.