Ges. Brito et al., EXAFS AND XRD STUDY OF THE STRUCTURAL EVOLUTION DURING ISOTHERMAL SINTERING OF SNO2 XEROGELS, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 8(1-3), 1997, pp. 269-274
The formation of an ordered (crystalline) phase during isothermal sint
ering of SnO2 monolithic xerogels, at 200, 250, 300, 400, 500, 600 and
700 degrees C, has been analyzed by the combined use of EXAFS and XRD
techniques. For the desiccated gel (110 degrees C), EXAFS results sho
w the formation of small microcrystallites with the incipient cassiter
ite structure. Between 110 and 250 degrees C, the dehydratation reacti
on leads to an amorphization evidenced by a decrease of the long and s
hort range crystallographic order. It is due to fissure formation in t
he xerogel network. For higher temperatures, a continuous coagulation
of the crystallites occurs, leading to grain growth. Grain and pore gr
owth obeys the same kinetic relation, so that the microstructure grows
by simple enlargement while its morphology is static.