Browsing by Author "Múzquiz, MS"

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    Average and local ordering of Yb2(Ti2-xYbx)O7-x/2 ‘stuffed’ pyrochlores: the development of a robust structural model
    (Elsevier, 2021-10-01) Mullens, BG; Zhang, Z; Avdeev, M; Brand, HEA; Cowie, BCC; D'Angelo, AM; Múzquiz, MS; Kennedy, BJ
    The long-range (average) and short-range (local) structures in the Yb2(Ti2-xYbx)O7-x/2 (x ​= ​0.00–0.67) series were studied using a combination of diffraction and spectroscopic techniques. The 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 anti-site disorder from x ​= ​0.335. The local structure, established from X-ray absorption near-edge structure (XANES), shows a gradual evolution of short-range disorder. The crystal field splitting energy of the Ti4+ ions decreases from 2.15 to 1.91 ​eV with increasing Yb3+ content, reflecting the increase in coordination number from 6 to predominantly 7. Electrochemical impedance spectroscopic studies show an increase in oxygen ionic conductivity by almost a factor of 3 upon doping with small amounts of Yb3+ (x ​= ​0.067). These results imply that the disordering across the anion and cation sublattices are different and inducing small amounts of disorder into the pyrochlore structure may lead to applications in solid-oxide fuel cells. © 2021 Elsevier Inc.
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    Effect of long- and short-range disorder on the oxygen ionic conductivity of Tm2(Ti2–xTmx)O7–x/2 “stuffed” pyrochlores
    (American Chemical Society, 2021-03-10) Mullens, BG; Zhang, Z; Avdeev, M; Brand, HEA; Cowie, BCC; Múzquiz, MS; Kennedy, BJ
    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