The effect of reducing atmosphere on the SrTiO3 based varistor-capacitor materials

The microstructural effect on the electrical properties of SrTiO₃ based varistor-capacitor materials sintered at various atmospheric conditions is investigated. Three sintering atmospheres are used by the decomposing source of liquid ammonia: (a) 30% H₂ + 70% N₂, (b) 50% H₂ + 50% N₂, and (c) 75% H₂ + 25% N₂ besides sintering in regular air as ambient. It is found that with the percentile increase of H₂ in the sintering atmosphere, the grain size and carrier concentration increase while varistor voltage V_10mA and nonlinear coefficient α decrease. It is suggested that more oxygen vacancies can be produced in strong reducing atmospheres, and the grain growth process is then controlled by the grain boundary diffusion, which leads to a lower sintering temperature. The results of Positron Annihilation Technique reveal that higher free carrier concentration can be generated that aids in changing electrical properties.