Powder composition for sintering into modified barium titanate semiconductive ceramic

摘要

To produce a modified barium titanate ceramic which is semiconductive and sufficiently high in breakdown voltage and has a low specific resistance at room temperature and a high positive temperature coefficient (PTC) of resistance, the invention provides a powder composition comprising (A) a basic mixture consisting of 45-85 mol % of BaTiO3 powder, 1-20 mol % of SrTiO3 powder, 5-20 mol % of CaTiO3 powder and 1-20 mol % of PbTiO3 powder, (B) a source of a dopant element such as Nb, Sb, Y, La or Ce to render the ceramic semiconductive, (C) a source of Mn such as MnC2O4 and/or a source of Cu such as CuO added such that the total amount of Mn and Cu is not more than 0.06 mol % on the basis of the quantity of the mixture (A) with proviso that the amount of Mn is not more than 0.025 mol % and (D) SiO2 amounting to 0.1-2.0 mol % on the basis of the quantity of the mixture (A). The BaTiO3 powder and the SrTiO3 powder are produced by calcining BaTiO(C2O4)2 and SrTiO(C2O4)2, respectively, and in each of these powders very fine primary particles agglomerate to constitute porous and coarse secondary particles (about 100-200 mu m). The PbTiO3 powder may be produced by calcining PbTiO(C2O4)2 so as to have nearly the same structure as the BaTiO3 and SrTiO3 powders. The aimed ceramic is produced by compacting the powder composition into a green body and sintering it at 1300 DEG -1400 DEG C.