Varistor and electrical properties of MgO•(Fe2O3)1-x(Bi2O3)x ceramics

In this study, MgO center dot(Fe2O3)(1-x)(Bi2O3)(x) (x = 0.01, 0.02, 0.04, 0.08) samples were prepared by the conventional ceramic process. Microstructure studies revealed that the samples contain MgFe2O4 grains surrounded by insulating Bi2O3-rich phases. DC electrical resistivity of the samples was increased by Bi2O3 content up to 1.1 M Omega.cm for the sample with x = 0.08. Current density-electric field investigations suggested that the samples with x = 0.01, 0.02 and 0.04 exhibited varistor properties. The sample with x = 0.01 showed excellent varistor properties with a non-linear coefficient of 45 and a threshold electric field value of 160 V/cm. Variation of D.C electrical conductivity versus temperature indicated that the activation energy values for the conduction were increased by Bi2O3 content from 0.334(5) eV to 0.857(5) eV. A.C electrical conductivity spectra of the samples obey the universal power law and the charge transport mechanism is based on electron hopping via sudden translational motion between the ferric and ferrous ions.