Microstructure and electrical properties of rare earth doped ZnO-based varistor ceramics

ZnO-based varistor ceramics doped with Nd2O3 and Y2O3 have been prepared by the conventional ceramics method. The phase composition, microstructure and electrical properties of the ceramics have been investigated by XRD, SEM and a V-I source/measure unit. The XRD and EDS analyses show the presence of ZnO, Bi2O3, Zn7Sb2O12, Y2O3, Nd-rich phase and Y-containing Bi-rich phase. The electrical properties analyzed show that the nonlinear coefficient of the varistor ceramics is in the range of 4.4-70.2, the threshold voltage is in the range of 247.1-1288.8 V/mm, and the leakage current is in the range of 1.51-214.6 μA/cm2. The 0.25 mol% Nd2O3 added varistor ceramics with 0.10 mol%Y2O3 sintered at 1050 °C exhibits excellent electrical properties with the high threshold voltage of 556.4 V/mm, the nonlinear coefficient of 61 and the leakage current of 1.55 μA/cm2. The results illustrate that doping Nd2O3 and Y2O3 in ZnO-based varistor ceramics may be a very promising route for the production of the higher threshold voltage and the nonlinear coefficient of ZnO-based varistor ceramics.