Effect of Y 2 O 3 , Nd 2 O 3 or Sm 2 O 3 on the microstructure and electrical properties of ZnVMnNbO varistor ceramics

This study addresses the different effect of doping 0.05 mol% Y2O3, Nd2O3 or Sm2O3 on the microstructure and nonlinear electrical properties of the ZnO–V2O5–MnCO3–Nb2O5 (ZnVMnNbO) ceramic sintered at 930 °C for 3 h using XRD, FESEM, EDS and I–V measurements. The results show the density and the microstructure homogeneity of the ZnVMnNbO ceramic increase with the addition of Y2O3, Nd2O3 or Sm2O3. Meanwhile, REVO4 (RE=Y, Nd or Sm) forms as the new secondary crystalline phase at ZnO grain nodal areas of the ZnVMnNbO ceramic which originally has Zn3(VO4)2, ZnMn2O4 and ZnV2O4 as the secondary phases. The addition of Y2O3 or Sm2O3 can effectively improve the nonlinearity coefficient of the ZnVMnNbO varistor ceramic from 33.6 of the RE-free sample to near 37 by increasing interface state density. In the contrast, Nd2O3 considerably reduces α to 25.9 by decreasing both barrier height (ΦB) and depletion layer width (ω).