Structural studies of nanocrystalline oxides

We report the results of structural studies of samples of nanocrystalline tin oxide, zirconia, magnesia, alumina and silica, prepared by sol–gel techniques (including the addition of silica to restrict grain growth) and high-energy ball milling. XRD, EXAFS/XANES and MAS-NMR analyses were used to characterise the materials. EXAFS showed that nanocrystals of ZrO2 and SnO2 prepared by sol–gel methods are highly crystalline, consistent with previous EXAFS studies of sol–gel prepared nanocrystalline oxides [A.V. Chadwick, M.J. Pooley, K.E. Rammutla, S.L.P. Savin, A. Rougier, J. Phys.: Condens. Matter, 15 (2003) 431.; A.V. Chadwick, G.E. Rush, in Nanocrystalline Metals and Oxides: Selected Properties and Applications, (Kluwer, New York), (2002), p.133.]. In contrast, the sol–gel prepared SiO2 appeared amorphous, even after prolonged heating at 1200 °C. The EXAFS of the ball-milled samples showed clearly attenuated signals that cannot be attributed solely to particle size. Ball milling of quartz crystals (which have a simple Q4) first broadens the NMR line and then generates Q3 and then Q2 lines indicating the generation of amorphous materials in the samples.