Effect of long- and short-range disorder on the oxygen ionic conductivity of Tm2(Ti2–xTmx)O7–x/2 “stuffed” pyrochlores
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Date
2021-03-10
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Publisher
American Chemical Society
Abstract
The long-range average and short-range local structures in the Tm2(Ti2–xTmx)O7–x/2 (x = 0.00–0.67) series were studied using a combination of diffraction and spectroscopic techniques. The long-range average structure, established from synchrotron X-ray and neutron powder diffraction data, shows the development of multiphase regions from x = 0.134 and the formation of antisite cation disorder from x = 0.402. The crystal field splitting of the Ti4+ ions, as derived from the Ti L3-edge X-ray absorption near-edge structure (XANES) spectroscopy, decreases gradually from 2.17 to 1.92 eV with increasing Tm3+ content (x), reflecting the increase in coordination number from 6 to predominantly 7. This is consistent with a gradual evolution of the short-range local disorder from x = 0.00 to 0.67. These results suggest that local disorder develops gradually throughout the entire composition range, whereas changes in the long-range disorder occur more suddenly. Electrochemical impedance spectroscopic results show an increase in oxygen ionic conductivity at 1000 °C, by a factor of 4 upon doping at x = 0.268. This suggests that inducing small amounts of disorder into the pyrochlore structure, by stuffing, may lead to applications of this material as a solid electrolyte in solid-oxide fuel cells. © 2021 American Chemical Society
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Keywords
Neutron diffraction, X-ray diffraction, Crystal field, Electrochemistry, Impedance, Pyrochlore
Citation
Mullens, B. G., Zhang, Z., Avdeev, M., Brand, H. E. A., Cowie, B. C. C., Múzquiz, M. S., & Kennedy, B. J. (2021). Effect of long- and short-range disorder on the oxygen ionic conductivity of Tm2(Ti2–xTmx)O7–x/2 “stuffed” pyrochlores. Inorganic Chemistry, 60(7), 4517–4530. doi:10.1021/acs.inorgchem.0c03363