Solid state sintering of nano-crystalline indium tin oxide

The sintering of single phase nano-crystalline In2O3 and ITO (In1.9Sn0.1O3.05) powders is reported and discussed with particular focus on the underlying mass transport mechanisms. The mass transport in the initial stage of sintering was surface diffusion, resulting in necking and coarsening, and grain boundary diffusion, accompanied by grain growth. Lattice diffusion caused significant densification at higher temperatures, leading to densities higher than 95%. The onset of densification and the maximum densification rate were shifted significantly to higher temperatures for ITO compared to In2O3. The reduced sintering rate of ITO was related to the higher valence state of Sn4+ relative to In3+, and due to precipitation of SnO2(s). The volatile sub-oxides In2O(g) and SnO(g) caused significant weight losses at high temperatures, particularly in the case of ITO and inert conditions. The sintering at intermediate temperatures is discussed with focus on heat treatment of ITO thin films.