An EXAFS study of nanocrystalline yttrium stabilized cubic zirconia films and pure zirconia powders

Detailed EXAFS (extended X-ray absorption fine structure spectroscopy) meas urements have been collected for two nanocrystalline forms of zirconia, nam ely, dense films of yttria-stabilized cubic zirconia (YSZ) and tetragonal p hase powders of pure ZrO2. Zr and Y K edge EXAFS spectra for the YSZ films with grain sizes of 6, 15, and 240 nm showed no major differences with the corresponding spectra of the bulk counterpart. This is clear proof that the se nanocrystalline films exhibit similar levels of disorder to that of larg e crystals. In particular, there is no support for the view that the interg rain regions are highly disordered, and the present work is consistent with recent EXAFS studies of other nanocrystalline oxides (SnO2 and ZnO) and me tals (Cu). The pure nanocrystalline ZrO2 powders were produced by calcining zirconium hydroxide, a widely used method of synthesising ZrO2. The Zr K e dge EXAFS of the powders, with grain sizes of 10 and 20 nm, yielded spectra in which the signal was strongly attenuated in comparison to the EXAFS bul k of ZrO2. A significant feature is the dramatically reduced amplitude of t he second peak in the Fourier transform, which is due to the Zr-Zr correlat ion. This feature is often interpreted as evidence of high levels of disord er in nanocrystalline materials. However, using the results from other tech niques, notably, NMR measurements, it is argued that the samples contained amorphous material due to an incomplete conversion of the hydroxide precurs or. Overall, the studies of the two types of nanocrystalline zirconia empha size the need for careful characterization of the materials prior to the ap plication of techniques such as EXAFS, which provide an average picture of the local structure.