A novel interfacial microstructure in SrTiO3 ceramics with Bi2O3-doping

A novel interfacial microstructure was found in Bi2O3-doped SrTiO3 ceramics. Bi-rich precipitates of sizes between 10 and 100 nm were observed at most grain boundaries. Using spatially-resolved EDS analysis, it was shown that these nano-precipitates had similar composition to Sr2Bi4Ti5O18 secondary phase formed at triple grain pockets. This was revealed by the same trends in both Bi/Ti and Sr/Ti ratios as a function of particle size. In addition to forming precipitates, Bi segregation was also detected at these boundaries. However, the segregation level was substantially lower compared with that at boundaries without precipitates. The latter type of boundaries was always covered with thin amorphous films. Such novel interfacial structure containing nano-particles at grain boundaries does not hinder the dielectric properties of the material and it cannot be simply incorporated into the grain–boundary–barrier–layer–capacitor (GBBLC) model, which requires continuous insulating layers.