The role of nanopowder particle surfaces and grain boundary defects in the sintering of ZnO ceramics

This work focuses on the characteristics of sintered ZnO ceramics and explores the role of source powder morphology in the process of sintering. The source ZnO powders had grained (d = 100 nm) and tetrapod-like (d=50-100 nm, l=3-10 μm) morphologies, they were compacted and sintered at 1200° C. The results have shown that ceramics sintered from the grained powder exhibit relatively high (8%) porosity at grain boundaries and as cavities within grains, which facilitates brittleness. Photoluminescence spectra for these ceramics besides a narrow exitonic band contain a broad "green" luminescence band attributed to defect states. The second ceramics sintered from the tetrapod-like powder has lower porosity (<2 %) Photoluminescence spectrum at 12 K revealed a narrow exitonic band with satellite peaks (1LO-Ex states) and almost negligible "green" band which is an indication of high quality of this ceramics. Experiments on bicrystals have shown that in the stage of grain growth the motion of grain boundaries is directly correlated to triple-junction mobility. The obtained results have been discussed from the point of contact phenomenon and evolution processes of the grain boundary microstructure at different sintering stages.