Structural morphology and nonlinear behavior of pure and co-doped Zn(1-x-y)Fe(x)M(y)O varistors with (M = Cu, Ni)

We report here structural morphology and nonlinear behavior of pure and co-doped Zn(0.90-x)Fe(0.1)M(x)O with (M = Cu, Ni and (x = 0.00, 0.10) and (0.00 ≤ y ≤ 0.20)) at different sintering temperatures (T(s) = 850 and 1000 °C). It is found that the co-doping of ZnO by (Fe + Cu) or (Fe + Ni) up to 0.30 does not deform the well-known wurtzite structure of ZnO, as well as pure and 0.1 of Fe-doped ZnO. The SEM micrographs did not show any secondary phases at the boundaries of grains as compared to ZnO, the average grain size is decreased for Fe and (Fe + Cu) samples, while it is increased for (Fe + Ni) samples. The nonlinear coefficient α and breakdown field E(B) are generally increased by 0.1 of Fe addition, but they are shifted to lower values as T(s) increases for all samples. Furthermore, they are gradually increased/decreased to higher/lower values for (Fe + Cu/Fe + Ni) samples up to 0.30 of co-doping content. The values of α and E(B) are increased from 30.06, 2115.38 V/cm for ZnO at 850 °C to 50.07, 5012 V/cm by (0.1Fe + 0.2Cu) co-doping, and from 23.53, 1956.52 V/cm to 45.58, 4750 V/cm at 1000 °C, while they are, respectively, decreased by (0.1Fe + 0.2Ni) to 13.19, 312 V/cm and 11.85, 172.42 V/cm. Similar behavior was generally obtained for nonlinear conductivity σ(L) and height of potential barrier φ(B), whereas the vice is versa for the behavior of leakage current J(k) and residual voltage K(r). Our results are discussed in terms of the comparative participation between the effects of co-doping of (Fe + Cu) and (Fe + Ni) to ZnO for supporting the potential barrier as compared to individual doping by Fe, Cu and Ni. This study perhaps recommended these samples for optoelectronic and ferromagnetic investigation after COVID-19 is over.