Influence of SiO2 addition on the PTCR characteristics of Ba0.92(Bi0.5K0.5)0.08TiO3 ceramics

As a candidate of lead-free positive temperature coefficient of resistivity (PTCR) materials, Ba0.92(Bi0.5K0.5)0.08TiO3–0.0005Nb2O5–xSiO2 (x = 0–0.03) ceramics were prepared by the conventional solid state reaction method. The effects of SiO2 addition on the crystal structure, microstructure and PTCR characteristics have been investigated. For x ≥ 0.01, the secondary phases of Ba2TiSi2O8 and BaSiO3 were found. SEM–EDS spectra revealed that the secondary phases existed at intergranular regions as liquid phase resulted in the enhancement of densification and the optimization of PTC effect. Scanning electron microscopy observations revealed that the grain size did not change greatly for all samples. With the increasing SiO2 content, the room temperature resistivity increased. For x = 0.001, the Curie temperature of the sample increased to 149.5 °C. A further study was conducted by impedance spectroscopy so as to study the effects of SiO2 addition on the resistivity of grains and grain boundaries.