Gradual structural evolution from pyrochlore to defect-fluorite in Y2Sn2-xZrxO7: average vs local structure
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We have studied the long-range average and local structures in Y2Sn2−xZrxO7 (x = 0−2.0) using synchrotron X-ray powder diffraction and X-ray absorption spectroscopy, respectively, and by theoretical methods. While the diffraction data indicate a clear phase transition from ordered pyrochlore to disordered defectfluorite at x ∼ 1.0−1.2, X-ray absorption near-edge structure (XANES) results at the Zr L3- and Y L2-edges reveal a gradual structural evolution across the whole compositional range. These findings provide experimental evidence that the local disorder occurs long before the pyrochlore to defect-fluorite phase boundary, as determined by X-ray diffraction, and the extent of disorder continues to develop throughout the defectfluorite region. The Zr and Y L-edge spectra are very sensitive to changes in the local structure; such sensitivity enables us to reveal the progressive nature of the phase transition. Experimental results are supported by ab initio atomic scale simulations, which provide a mechanism for disorder to initiate in the pyrochlore structure. Further, the coordination numbers of the cations in both the defect-fluorite and pyrochlore structures are predicted, and the trends agree well with the experimental XANES results. The calculations predict that the coordination of cations in the Y2Zr2O7 defect-fluorite (normally considered to be 7 for all cations) varies depending on the species with the average coordination of Y and Zr being 7.2 and 6.8, respectively. © 2013, American Chemical Society.
X-ray diffraction, Pyrochlore, Zirconium, Cations, Defects, Fluorite
Zhang, Z., Middleburgh, S. C., de los Reyes, M., Lumpkin, G. R., Kennedy, B. J., Blanchard, P. E. R., Reynolds, E., & Jang, L.-Y. (2013). Gradual structural evolution from pyrochlore to defect-fluorite in Y2Sn2-xZrxO7: average vs local structure. Journal of Physical Chemistry C, 117(50), 26740-26749. doi:10.1021/jp408682r