Non-linear coefficient of BaTiO3-doped ZnO varistor

The effect of additions up to 9.6%wt BaTiO₃ on grain growth and microstructure in ZnO samples sintered at 1300°C has been studied using scanning electron microscopy, energy dispersive X-ray, X-ray diffraction and impedance analyser as techniques. The sample doped with 1.6%wt BaTiO₃, leads to grain size increasing and forms (BaO_10.89Ti_3.93Zn_2.03 and Ba₄O₂₇Ti₁₁Zn) solid solutions with ZnO. A homogeneous structure was obtained whereas with further additions 3%wt the structure was inhomogeneous and the solid solutions formed in the first segregate to grain boundaries. Afterwards, an excess of 9.6%wt BaTiO₃ leads to BaTiO₃ phase segregation locating on the surface of the sample and in the grain boundaries near the junctions between matrix grains. Experimental I-V current-voltage characteristics show that BaTiO₃ as additive in ZnO varistors, increases the non-linear coefficient (α) and the breakdown voltage. The highest non-linearity was obtained for 9.6%wt BaTiO₃ content with α = 121.03 and 1.79 μA in leakage current. The average breakdown voltage per grain boundary (Vgb) was evaluated in the ranges 1.7-3.46 V/gb and 1.34-2.54 V/gb in agreement with the literature.