Effect of Al-doping on the Grain Growth of ZnO

Abstract

Grain growth of ZnO in liquid phase sintering of ZnO–0.5 mol%Bi 2 O 3 ceramics has been studied by increasing the doping amount of Al 2 O 3 from 25 ppm to 200 ppm. Al 2 O 3 was doped using an aluminum nitrate aqueous solution. When 50 ppm of Al 2 O 3 was doped to ZnO ceramics, abnormal grain growth was observed, while 75 ppm Al 2 O 3 retarded grain growth. Doping of Al 2 O 3 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 Al 2 O 3 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 Al 2 O 3 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.