Effect of ZnO doping on microstructural and electrical properties of SnO2–Ta2O5 based varistors

Highlights: ► SnO2–Ta2O5–ZnO varistors. ► Doping effect of ZnO on SnO2–Ta2O5 based varistors. ► Optimizing doping of ZnO in SnO2–Ta2O5 based varistors. - Abstract: SnO2–Ta2O5 based varistors doped with 0–2.0 mol% of ZnO were prepared by sintering the samples at 1450 °C for 2 h with conventional ceramic processing method. The doping effect of ZnO on the microstructural and electrical properties of the as-prepared SnO2–Ta2O5 based varistor ceramics was investigated. The change in SnO2 lattice parameter and EDX analysis both confirmed the doping of Zn ions into SnO2 grains, although the identified phase was only SnO2 (cassiterite) by X-ray diffraction in detection limit. The microstructure observation indicated that the doped ZnO can facilitate the sintering of the varistor ceramics. The measured electric-field/current-density characteristics of the samples revealed that the nonlinear exponents and varistor voltage increased with increasing doping amount of ZnO when the ZnO content was no more than 0.5 mol%; and more addition of ZnO would cause a decrease in nonlinear exponent and varistor voltage of the ceramic varistors.