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% H-2 + 70% N-2, (b) 50% H-2 + 50% N-2, and (c) 75% H-2 + 25% N-2 besides sintering in regular air as ambient. It is found that with the percentile increase of H-2 in the sintering atmosphere, the grain size and carrier concentration increase while varistor voltage V-10mA and nonlinear coefficient alpha 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.