We report here the structural and electrical properties of Zn0 .95M0 .05O ceramic varistors, M = Zn, Ni and Fe. The samples
were tested for phase purity and structural morphology by using X-Ray diffraction XRD and scanning electron microscope
SEM techniques. The current-voltage characteristics J-E were obtained by dc electrical measurements in the temperature range
of 300 – 500 K. Addition of doping did not influence the hexagonal wurtzite structure of ZnO ceramics. Furthermore, the
lattice parameters ratio c/a for hexagonal distortion and the length of the bond parallel to the c axis, u were nearly unaffected.
The average grain size was decreased from 1.57 µm for ZnO to 1.19 µm for Ni sample and to 1.22 µm for Fe sample. The
breakdown field EB was decreased as the temperature increased, in the following order: Fe > Zn > Ni. The nonlinear region
was clearly observed for all samples as the temperature increased up to 400 K and completely disappeared with further increase
of temperature up to 500 K. The values of nonlinear coefficient, α were between 1.16 and 42 for all samples, in the following
order: Fe > Zn > Ni. Moreover, the electrical conductivity σ was gradually increased as the temperature increased up to 500 K,
in the following order: Ni > Zn > Fe. On the other hand, the activation energies were 0.194 eV, 0.136 and 0.223 eV for all
samples, in the following order: Fe, Zn and Ni. These results have been discussed in terms of valence states, magnetic moment and thermo-ionic emission, which were produced by the doping, and controlling the potential barrier of ZnO