X‐ray Absorption Studies of Ceria with Trivalent Dopants

The local structural environments of Sc 3+ and Gd 3+ in ceria were studied for the first time by using EXAFS (extended X‐ray absorption fine structure) and XANES (X‐ray absorption near edge structure) spectroscopy. Our results indicate that Sc 3+ in 10‐mol%‐Sc 2 O 3 ‐doped ceria has a 7‐fold‐coordinated Sc‐ordered structure with two different Sc─O distances (2.13 and 2.26 Å). An octahedrally coordinated Sc─O cluster is present in 5 mol% Sc 2 O 3 ─5 mol% Gd 2 O 3 ─CeO 2 , because of the strong scavenging effect of Sc 3+ ions on oxygen vacancies created by Gd 3+ . The Gd 3+ in this sample is largely unassociated. Sc 2 O 3 (5 mol%) and Gd 2 O 3 (5 or 10 mol%) form random solid solutions with CeO 2 . These results are consistent with the current concept of defect structures in this structural family.