"Controlled SnO2 nanocrystal growth in SiO2-SnO2 glass-ceramic monoliths"

Crack-free (100-x) SiO2 - x SnO2 glass-ceramic monoliths have been prepared by the sol-gel method obtaining for the first time SnO2 concentrations of 20% with annealing at 1100°C. Heat-treatment resulted in the formation and growth of SnO2 nanocrystals within the silica matrices. Combined use of FT-Raman spectroscopy and in-situ high-temperature X-Ray diffraction (HTXRD) shows that SnO2 particles begin to crystallize in the cassiterite-type phase at 80°C and that their average apparent size remains around 7 nm, even after annealing at 1100°C. Nanocrystal sizes and size distributions determined by low-wavenumber Raman are in good agreement with those obtained from TEM measurements. Results indicate that the formation and the growth of SnO2 nanocrystals impose a residual porosity in the silica matrix.