SiO2/SnO2 and Sn/Sb-oxide/SiO2 gel-derived composites. Part 2: Thermal evolution and phase analysis

The thermal behaviour of samples with nominal composition 80/20=SiO₂/SnO₂, class B, 76.8/19.2/4.0=SiO₂/SnO₂/Sb₂O₅, class C₁, and 76.8/19.2/2.0/2.0=SiO₂/SnO₂/Sb₂O₅/Sb₂O₃, class C₂, is studied in the interval 25–1050°C by various instrumental methods. Results on these classes of samples, obtained from alkoxide precursors, are compared themselves and with samples of class A obtained from Si(OEt)₄ and SnCl₄. The segregation and crystallization of SnO₂ occurs at 400°C in the presence of microdomains of SnO₂·nH₂O in the SiO₂ gel matrix (class A), whereas it is observed at 700°C for samples B and C composed of Sn and Sb cations homogeneously dispersed in SiO₂. This fact implies different mechanisms of SnO₂ nucleation and growth. The crystallization of SiO₂ is observed at 1200°C for samples A, at 1050°C for B and at 800°C for C. For this latter, the presence of Sb-oxide/ SiO₂ reactive glass is invoked to the low-temperature crystallization of SiO₂. G. Carturan, R. Ceccato, R. Campostrini, G. Principi, and U. Russo, submitted to J. Sol-Gel Sci. Tech.