Effect of Al-doping on the Grain Growth of ZnO

Abstract

Grain growth of ZnO in liquid phase sintering of ZnO–0.5 mol%Bi2O3 ceramics has been studied by increasing the doping amount of Al2O3 from 25 ppm to 200 ppm. Al2O3 was doped using an aluminum nitrate aqueous solution. When 50 ppm of Al2O3 was doped to ZnO ceramics, abnormal grain growth was observed, while 75 ppm Al2O3 retarded grain growth. Doping of Al2O3 to pure ZnO ceramics did not cause abnormal grain growth,but simply retarded grain growth . The ratio of diameters of these grain sizes sintered at 900° C: d (abnormal grain growth)/d(retarded grain growth) is 20–100. Mechanisms of abnormal grain growth and retardation are proposed as follows. When the doped amount of Al2O3 was 50 ppm, aluminum compound thin films which were formed around ZnO grains at a low temperature and retarded grain growth disappeared suddenly by diffusion into the ZnO grain and ZnO grains grew suddenly. When the doped amount of Al2O3 was 75 ppm and the aluminum compound film was thick enough, part of the film remained unchanged even when a considerable proportion of the aluminum diffused mainly into the ZnO to reach solubility, retarding grain growth.