Effect of SrO on the electrical barrier formation and microstructure of TiO2 varistors

TiO2-based varistor materials with SrO dopants were prepared by the mechanical mixed oxides synthesis technique using conventional sintering at 1400 °C. IV and microstructural characterization were performed. The composition range of 0.50-2.00 mol % SrO was studied and compared to pure TiO2. Experimental evidence shows that small amounts of SrO improve the nonlinear properties of the samples significantly. Optimal varistor characteristics α = 5.50 and Eb = 345 V/cm, were obtained with 1.00 mol % SrO-doped TiO2. SrO in larger amounts causes the formation of precipitates of the SrTiO3 layer on the microstructure, being deleterious to the electrical properties. Therefore, dopants such as SrO or TiO2 play a special role in the morphology of the grain boundary and nonlinear response of these materials. An atomic defect model based on the double barrier Shottky type can be adopted to explain the formation of electrical barriers in TiO2 grain boundaries.