Effect of Bi_2O_3 doping methods on the positive temperature coefficient property of Ba_(0.999)(Bi_(0.5)Na_(0.5))_(0.001)TiO_3 ceramics

摘要

Lead-free positive temperature coefficient of resistivity ceramics based on 0.999BaTiO_3–0.001(Bi_(0.5)Na_(0.5))TiO_3 solid solution were fabricated by the conventional ceramic technique, while Bi_2O_3 was doped directly or after pre-calcining, in the molar ratio of Bi_2O_3:Na_2CO_3:TiO_2 (G) = 1:1:4,1.005:1:4, 1.01:1:4, and 1.015:1:4, respectively. There are two synthesizing route, i.e. the materials with G= 1.005:1:4 were pre-calcined at 780℃ firstly and then doped into the basic materials and the materials were directly doped by G= 1.01:1:4 into the starting materials with another holding process at 850 ℃ for 30 min during co-calcining with BaTiO_3, both of which could obtain samples with the maximum Curie temperature about 144 ℃. The latter also possessed comparatively lower room temperature resistance about 22.0Ω. A further study was deserved to carry out in an attempt to obtain ceramics with higher Curie temperature via more Bi_2O_3-doping.