Effect of Bi2O3 doping methods on the positive temperature coefficient property of Ba0.999(Bi0.5Na0.5)0.001TiO3 ceramics

Lead-free positive temperature coefficient of resistivity ceramics based on 0.999BaTiO3–0.001(Bi0.5Na0.5)TiO3 solid solution were fabricated by the conventional ceramic technique, while Bi2O3 was doped directly or after pre-calcining, in the molar ratio of Bi2O3:Na2CO3:TiO2 (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 °C 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 °C for 30 min during co-calcining with BaTiO3, both of which could obtain samples with the maximum Curie temperature about 144 °C. The latter also possessed comparatively lower room temperature resistance about 22.0 Ω. A further study was deserved to carry out in an attempt to obtain ceramics with higher Curie temperature via more Bi2O3-doping.