A study of V-shaped PTC behaviour of Sr0.4Pb0.6TiO3 ceramics

Yttrium-doped Sr0.4Pb0.6TiO3 ceramics were prepared at relatively low sintering temperature using conventional sintering technology. The sintered ceramics exhibit novel NTC–PTC composite effects. The influences of doping PbO and SiO2 on the properties of Sr0.4Pb0.6TiO3 ceramics were compared. It was found that suitable PbO additives reduce the room-temperature resistivities (ρRT) of Sr0.4Pb0.6TiO3 ceramics and weaken their NTC effects, but the effect of doping SiO2 is reverse. The XRD analyses show that SiO2 additives can cause Pb2+ ions segregating out from Sr0.4Pb0.6TiO3 lattices and form PbO·SiO2 phase. It is estimated that the strong NTC effects of Sr0.4Pb0.6TiO3 ceramics should be closely related to the Pb2+ immigration. The domain structure, morphology and compositional distribution of Y-doped Sr0.4Pb0.6TiO3 ceramics were investigated using TEM, SEM and EDAX respectively. The results of EDAX indicate that the Pb/Sr ratio on the grain boundaries is slightly lower than that in the grains. According to the results, the V-shaped PTC behaviors of (Sr,Pb)TiO3 ceramics are discussed.