INHIBITED GRAIN GROWTH IN SOL-GEL SYNTHESIS OF NANOCRYSTALLINE TRANSITION METAL OXIDES

摘要

Crystallite growth upon calcination of hydrous transition metal oxide gels can be effectively inhibited by replacing the surface hydroxyl group prior to calcination with methyl siloxyl, which does not condense and can produce small secondary-phase particles which restrict advancing of grain boundaries at elevated temperatures. This pretreatment allows the gel, upon calcination, to crystallize, while suppressing growth of existing crystals. As a result, the gel is uniformly crystallized to give nanocrystallites with a size less than 10 nm. Examples of SnO_2 and ZrO_2 are given. For the latter, the pretreatment also enhances the metastability of tetragonal crystallites.