Abstract
Surfaces of thermally reduced yttria, either pure (5 N) or doped with Zr, are studied by means of x‐ray absorption spectroscopy (surface‐extended x‐ray absorption fine structures), x‐ray‐induced Auger electron spectroscopy and x‐ray photoelectron spectroscopy. No Zr surface segregation is observed for the solid solutions considered, (100 − x) YO~1.5~ + __x__ZrO~2~ (with x = 5.3 or 13), whatever the thermal treatment experienced.
In pure and Zr‐doped yttria, the concentration of oxygen vacancies is estimated at the surface as a function of reduction time: while, in the early stages, oxygen deficiency appears to be spatially homogeneous, after a certain time the first atomic layers are much more oxygen‐depleted than the bulk. The introduction of oxygen vacancies in the lattice leads to a modification of the YO bond, which corresponds to a decrease of the local atomic charge on the remaining oxygen atoms, as observed from the Auger O KLL lineshape. This decrease in the ionic character of the bond causes an increase in the total polarizability and of the surface optical dielectric constant, as deduced from O and Y Auger parameter measurements. These variations are weaker in the doped samples, which could be due to a smaller static disorder compared to that of pure samples.