THE STRUCTURE OF CONFINED OXYGEN IN SILICA XEROGELS

The microscopic structure of oxygen confined in silica xerogels has be en studied as a function of temperature. In large pores, a crystalline solid forms with a structure consistent with that of the bulk. The si ze of the crystallites is much larger than the pore size, indicating t hat cooperative effects among pores ape important in freezing. As the pore size is decreased, a crossover occurs where solidification result s in an amorphous phase in the pores. The resulting amorphous phase is solid but is less ordered than the liquid phase.