Soft core phenomenon of ZnO varistors doped with rare-earth oxides

The effects of rare-earth oxide Ce₂O₃ and Gd₂O₃ on the electrical properties of ZnO-Bi₂O₃ based ceramics were investigated. The non-uniform distribution of voltage gradient along axial direction was found, which leading to the decrease of the average voltage gradient of the sample with the increase of its size. Obvious difference in average grain size along axial direction could not be observed by scanning electron microscope. The distribution of Schottky barrier height was found non-uniform along axial direction by measuring I-T response of thin layers cut from the sample, which is likely to be caused by non-uniform distribution of oxygen element due to the addition of rare-earth oxides.