Effects of Pr₂O₃ doping on the electric properities of the high-voltage ZnO varistor

Nanoscale ZnO composite powders doped with the rare earth Pr₂O₃ were synthesized by solid-state reaction at low temperature. The high-voltage ZnO varistors were prepared through the sintering of the above-mentioned powders at different temperature. The powders and high-voltage ZnO varistors were characterized by XRD, specific surface analysis, scanning electron microscope, TEM and so on. As a comparison, the ZnO varistors indoped by Pr₂O₃ were studied, and the mechanism of Pr₂O₃ doping was discussed in detail. The results show that the doped Pr₂O₃ tends to segregate at grain boundaries of ZnO varistors, and can activate the ZnO grain boundaries and promote the growth of crystal at low sintering temperature (1030-1130 ℃). Furthermore, the Pr₂O₃ doping leads to the formation of texture among the grain boundaries of ZnO varistors prepared at 1080 ℃, and make the doped-Pr₂O ZnO varistors more uniform and solid than that of the undoped-Pr₂O₃ ZnO varistors, which are helpful to the improvement of the grain boundaries of ZnO varistors, and enhancement of the electronic properties of ZnO varistors.The high-voltage ZnO varistor of doped Pr₂O₃ with the best electronic properties was prepared at 1080 ℃, which has a potential gradient of 864.39 V/mm, a nonlinear coefficient of 28.75 and a leakage current of 35 μA.