Ges. Brito et al., SAXS MEASUREMENTS OF THE POROSITY IN CU(II)-DOPED SNO2 XEROGELS DURING CRYSTALLIZATION, Journal of non-crystalline solids, 217(1), 1997, pp. 41-47
The small-angle X-ray scattering (SAXS) technique was used to study th
e porosity which develops in Cu(II)-doped SnO2 monolithic xerogels dur
ing crystallization. The influence of the upper temperature of heat-tr
eatment and of Cu(II) content on the structure was determined. Previou
s studies of the porosity in undoped SnO2 samples treated at temperatu
res ranging from 300 up to 600 degrees C demonstrated the existence of
a bimodal size distribution (one distribution was due to intra-aggreg
ate and the other to inter-aggregate pores). However, the SAXS data fr
om Cu(II)-doped samples heated to 500 degrees C had a single mode dist
ribution due only to inter-aggregate pores. Doped samples isothermical
ly treated at 500 degrees C were studied by the in situ SAXS technique
. The time evolution of the scattering intensity function, or structur
e function of the porous material, exhibits a dynamical scaling proper
ty. The asymptotic behavior at high q (wave numbers) of the scaled fun
ction and consequently the nature and morphology of the porosity inter
face are a function of Cu(II) content. The kinetic exponents predicted
by the statistical theory for the structure function suggest that the
mechanism of porosity coarsening is controlled by surface diffusion.
(C) 1997 Elsevier Science B.V.