Evolution in structural and optical properties of stannic oxide xerogel upon heat treatment

Upon consecutive heat treatments at increasing temperatures, the microstruc ture of solution-sol-gel-derived stannic oxide (SnO2) xerogel evolves in th ree stages: (I) below 300 degrees C, characterized by extensive dehydroxyla tion and gel shrinkage,vith little grain growth and surface loss; (II) betw een 300 degrees and 500 degrees C, by extensive crystallization, leading to dramatic surface loss (by 70%); and (III) above 500 degrees C, by grain gr owth. Concurrently, the UV-absorption edge shows red shifts during stages I and II and blue shifts during stage III, resulting in distinct color varia tions. The edge displacement bears a close correlation with a Raman "defect band" at similar to 305-328 cm(-1).