Abstract
We investigated the effects of the re-oxidation temperature and time on the positive temperature coefficient (PTC) of resistivity characteristics of Sm-doped BaTiO₃ sintered at 1200~1260℃ for 2 h in a reducing atmosphere (3% H₂/N₂), followed by re-oxidization processes in air, in which re-oxidization temperature and time were 600~1000℃ and 1~10 h, respectively. The result reveals that Smdoped (Ba,Ca)TiO₃ ceramics fired in a reducing atmosphere exhibit low PTC characteristics, whereas the sample re-oxidized at 800℃for 1 h in air exhibit pronounced PTC characteristics. The room-temperature resistivity and jumping characteristics of resistivity (ρmax/ρ 25℃ ) decrease with Sm contents. The PTC characteristics with reoxidization time at 800℃ have improved about 2~3 orders of magnitude whereas differed according to the sintering temperature. The 0.7 at% Sm-doped (Ba,Ca)TiO₃ samples reveal the best PTC characteristics in the present range of formula and processes.
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