An EXAFS Study of Nanocrystalline Yttrium Stabilized Cubic Zirconia Films and Pure Zirconia Powders

Abstract

Detailed EXAFS (extended X-ray absorption fine structure spectroscopy) measurements have been collected for two nanocrystalline forms of zirconia, namely, dense films of yttria-stabilized cubic zirconia (YSZ) and tetragonal phase powders of pure ZrO 2 . 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 these nanocrystalline films exhibit similar levels of disorder to that of large crystals. In particular, there is no support for the view that the intergrain regions are highly disordered, and the present work is consistent with recent EXAFS studies of other nanocrystalline oxides (SnO 2 and ZnO) and metals (Cu). The pure nanocrystalline ZrO 2 powders were produced by calcining zirconium hydroxide, a widely used method of synthesising ZrO 2 . The Zr K edge 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 bulk of ZrO 2 . A significant feature is the dramatically reduced amplitude of the second peak in the Fourier transform, which is due to the Zr-Zr correlation. This feature is often interpreted as evidence of high levels of disorder in nanocrystalline materials. However, using the results from other techniques, notably, NMR measurements, it is argued that the samples contained amorphous material due to an incomplete conversion of the hydroxide precursor. Overall, the studies of the two types of nanocrystalline zirconia emphasize the need for careful characterization of the materials prior to the application of techniques such as EXAFS, which provide an average picture of the local structure.

Local structures surrounding Zr in nanostructurally stabilized cubic zirconia: Structural origin of phase stability

“…As a side remark, we note that Rush et al 19 also reported a much reduced coordination number of 4 for the nearest O shell from the central Zr atom in nanocrystalline zirconia. However, the Zr-O and Zr-Zr distances of 2.13 and 3.41 Å, respectively, in their sample is substantially different from our values of 2.06-2.10 Å and 3.59-3.62 Å for the three pure-cubic-phase samples, respectively.…”

XANES and EXAFS study of the local order in nanocrystalline yttria-stabilized zirconia

“…36 This is in contrast with the conclusions reached by Rush et al on nanocrystalline YSZ films. 37 They found that the 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 these nanocrystalline films exhibit similar levels of disorder to that of large crystals.…”

First-principles thermodynamic modeling of atomic ordering in yttria-stabilized zirconia

“…8 As precise experimental atomic ordering data of nanostructured materials are still difficult to obtain, computationally based theoretical two-body radial structural analysis is an important tool to complement experimental determinations of the coordination and distribution of species. [29][30][31] A theoretical discrete radial distribution function is simply obtained here by analyzing the thermally equilibrated LMC configurations, as an average over all equivalent sites. Of further interest is to determine how defects and dopants associate in groups.…”