The effect of TiO2 addition on microstructure and electrical properties of SnO2 varistors prepared from nanomaterials

The effects of various amounts of TiO2 in the composition of SnO2-based varistors made from nano-sized materials on microstructure and electrical properties have been investigated. Titanium oxide acts as both a densifier and grain growth enhancer resulting in relative densities in the range of 96–99%. The addition of TiO2 from 0 to 3 mol% has changed the average grain size from 1.8 to 5 μm. The introduction of TiO2 causes precipitation of Ta2O2.2 phase on the sample surfaces. The lowest breakdown field, 2 kV/cm, has been observed for the sample containing 0.75 mol% of TiO2, and the best surge-withstand parameters (residual voltage ratio, 2.4, withstanding surge current density, 5 kA/cm2) have been observed for the sample with 0.25 mol% TiO2. Larger amounts of TiO2 have had an adverse effect on the surge-withstand capability due to the loss of homogeneity in the samples caused by tantalum transpiration.