Compositional analysis and electrical properties of Sb, Mn-doped barium strontium titanate PTCR ceramics with TiO2 and SiO2 sintering additives

The secondary phase compositions in Sb-doped (Ba, Sr)TiO3 ceramics containing SiO2 and excess TiO2 sintering additives have been examined by XRD, BEI and EPMA techniques. It is shown that alongside the primary (Ba0.797Sr0.2Sb0.003)TiO3 phase, (Ba1.95Sr0.05)2(Ti1.2Si1.8)O8 and Sb-doped (Ba0.99Sr0.01)6 Ti17O40 phases form at the intergranular regions. Substitution of up to 0.04 mol% MnO2 enhances the PTCR effect, giving a ratio qmax/qmin ~ 7 · 105 for the optimum 0.04% MnO2 composition. At this level Mn cannot be detected in the microstructure by EPMA, however in insulating samples containing 0.08 mol%of MnO2, it was detected in the (Ba0.99Sr0.01)6Ti17O40 intergranular phase