Evolution in Structural and Optical Properties of Stannic Oxide Xerogel upon Heat Treatment

Abstract
Upon consecutive heat treatments at increasing temperatures, the microstructure of solution–sol–gel‐derived stannic oxide (SnO2) xerogel evolves in three stages: (I) below 300°C, characterized by extensive dehydroxylation and gel shrinkage with little grain growth and surface loss; (II) between 300° and 500°C, by extensive crystallization, leading to dramatic surface loss (by 70%); and (III) above 500°C, by grain growth. Concurrently, the UV‐absorption edge shows red shifts during stages I and II and blue shifts during stage III, resulting in distinct color variations. The edge displacement bears a close correlation with a Raman “defect band” at ∼305–328 cm−1.