Average and local ordering of Yb2(Ti2-xYbx)O7-x/2 ‘stuffed’ pyrochlores: The development of a robust structural model

Abstract 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.