Effect of Temperature and Magnetic Dopants on Particle size and Electrical Properties of ZnO Ceramic Varistor

Abstract

We report here structural and electrical properties of Zn0.95 M0.05O ceramic, M = Zn, Co and Mn. It is found that addition of magnetic doping did not influence the hexagonal wurtzite structure of ZnO. Furthermore, the lattice parameters ratio c/a for hexagonal distortion and the length of the bond parallel u to the c axis were nearly unaffected. The average crystalline diameters, deduced from XRD analysis are 83.75, 72.86 and 70.97 nm for Zn, Mn and Co, which are 15 times lower than those obtained from FESEM micrographs (1570, 1380 and 1150 nm). The breakdown field EB was decreased as the temperature increased, in the following order: Mn> Zn > Co. The nonlinear region was 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 1.65 and 56 for all samples, in the following order: Mn> Zn > Co. Moreover, the electrical conductivity σ was gradually increased as the temperature increased up to 500 K, in the following order: Co > Zn > Mn. On the other hand, the activation energies were 0.194, 0.155 eV and 0.231 eV for all samples, in the following order Mn, Zn and Co. 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.