Roles of Dopants in Sintering Behavior of ZnO-Based Varistor
Three series of ZnO-based materials with different doping levels were prepared. The correlation between the composition and microstructure, and the roles of main dopants, Bi2O3 and Sb2O3, in the sintering behaviors were proposed. Both Bi2O3 and Sb2O3 evaporated at 1115°C, but the amount of them, in which bismuth is the majority, is not significant. Bi2O3 functioned mainly as liquid during sintering to promote the sintering of ZnO, but it doesn’t mean the materials will be denser. The bismuth-rich phase retracted into small pores during cooling, leaving the big pores as voids at room temperature. More Bi2O3 added would result in less increase in material densities and dramatic decrease in relative densities, and a little bit increase in grain sizes of matrix ZnO. Sb2O3 would react with ZnO matrix into spinel, Zn7Sb2O12, which will pin at the grain boundary of ZnO to control the ZnO grain growth. The more Sb2O3 added, the smaller the grain sizes of ZnO. Appropriate amount of Sb2O3 added will yield denser materials.
Wei Pan and Jianghong Gong
Z. J. Peng et al., "Roles of Dopants in Sintering Behavior of ZnO-Based Varistor", Key Engineering Materials, Vols. 368-372, pp. 479-482, 2008