Effects of Bi 1/2Na 1/2TiO 3 on the Curie temperature and the PTC effects of BaTiO 3-based positive temperature coefficient ceramics

Abstract

In order to prepare lead-free BaTiO 3-based PTC with middle Curie point, the incorporation of Bi 1/2Na 1/2TiO 3 (abbreviated to NBT) into BaTiO 3-based ceramics was investigated on samples containing 0.1, 0.5, 1, 1.5, 1.6, 1.8, 2 mol% of NBT. It was found that for all samples containing up to 1.5 mol%, the Curie temperature was obviously improved with the increasing of NBT content, and the T C raised to 150 °C from 97 °C just only 1.5 mol% NBT added. Because A O bonds were weakened, which induced that Ti O bonds were strengthened correspondingly, and the actions between Ti 4+ (a departure of center) and its near O 2− were so strong that Ti 4+ could not resume its seat except that it was under the higher temperature, hence the Curie temperature was improved. At the same time, the PTC effects were also meliorated which attributed to vast electron capture centers formed by Bi 2O 3 acting with MnO. However, when the amount of NBT exceeded 1.5 mol%, the samples were dielectric material and had no PTC effects, but it was worth noting that the ρ– T curve of the samples sintered in reducing atmosphere was linear.