Rare earth oxides
Ceria CeO2
| CeO2 has the fluorite structure with 8-coordinate Ce and 4-coordinate O |
Lanthanide sesquioxides Ln2O3 can adopt one of three structures: Types A, B or C
| The 'A' type (hexagonal) structure is the stable form for large (early)Ln3+. It has 7-coordinate Ln3+ with 6 oxide ions arranged approximately octahedrally and the seventh oxide ion above one of the faces of the octahedron. | |
| The'B' type (monoclinic) structure is rather complicated. It has threee distinct Ln3+sites: one is 6-coordinate and octahedral; the other two sites are 7-coordinate mono-capped trigonal prisms. The 'B' type structure is adopted in the middle of the series. | |
| The 'C'-type (cubic) structure is related to the fluorite (or CeO2) structure by the ordered removal of one quarter of the anions. This structure is adopted by the later lanthanides and has 6-coordinate Ln3+ ions. |