Abstract: (Ba, Bi, Na)TiO₃-based PTCR Ceramics (BBNMT) doped with Nb₂O₅ (0.1mol%, 0.3 mol%, 0.5mol%, 0.7mol%) were prepared by the solid state reaction method and annealing in the reduction atmosphere. The microstructures and electrical properties of BBNMT were investigated. The results show that with the increase of Nb₂O₅ contents, the grain size increases firstly and then decreases, which indicates that there exists an optimal content of Nb₂O₅. The low resistivity PTC ceramic materials are obtained when the content of Nb₂O₅ is 0.5mol% with the room temperature resistivity(ρ₂₅) of 1.06×10³Ω·cm, the Curie temperature (T_c) of 183℃, and the resistivity jump (ρ_max/ρ_min) of 1.0×10⁴. By analyzing the impedance spectroscopy, the influence of the grain phase, grain boundary phase and “shell phase” on the resistivity are discussed, the interaction mechanism of Nb₂O₅ donor in PTCR ceramics are also studied.

Key words: PTCR, lead-free, high curie temperature, (Bi_1/2Na_1/2) TiO₃