Rare-earth (RE)-doped ceria (CeO2) with cubic fluorite-type (F) structure is an important ionic conductor, which has relatively high ionic conductivity and can be used as an electrolytic material in intermediate temperature solid oxide fuel cells (SOFCs). In fact, the weak ionic conductivity of pure CeO2 is enhanced by the substitution of Ce4+ by a proper amount of alliovalent ion, such as trivalent lanthanides. In this way the diffusion of O2– through the oxygen vacancies arising from doping is promoted as long as the F structure of ceria is retained. For this reason it is particular interesting the investigation of the structural behavior of the RE-doped ceria in the field of stability of the F structure.
In this work we have studied the local structure around Ce and Lu of (Ce1-xLux)O2-x/2 using X-ray absorption spectroscopy in a doping range x between 0 and 0.4 which is the field of stability of the F structure for this system.
The analysis of the EXAFS spectra has shown that as soon as the smallest amount doping atoms is introduced in the structure the oxygen coordination of Ce decreases and remains essentially constant for the whole stability range of the F structure. The analysis at both Ce and Lu L3 edges have evidenced similar oxygen coordination indicating as that Lu substitutes Ce in the range of stability of the F structure.
As for the interatomic distances, while diffraction techniques cannot distinguish between Ce-O and Lu-O, the EXAFS analysis shows that Ce and Lu coordinate with oxygen atoms with different distances although Lu substitutes Ce in the F structure evidencing that the dopant element produced a local structural distortion not detectable by long range structural techniques.
A comparison of the structural behavior with other similar systems will be shown.