Crystal structures of some fluorite-related M7O12 compounds
1976; Elsevier BV; Volume: 19; Issue: 2 Linguagem: Inglês
10.1016/0022-4596(76)90156-0
ISSN1095-726X
Autores Tópico(s)Rare-earth and actinide compounds
ResumoPowder X-ray diffraction techniques have been used to determine the crystal structures of Ti3Sc4O12, Nb1.5Sc5.5O12, NbSc6O11F, NbSc5HfO12, Zr3Er4O12, and Hf3Sc4O12 and to reexamine the structures of Zr3Sc4O12 and Zr3Yb4O12. All the compounds have the same fluorite-related superstructure as reported previously for Pr7O12, UY6O12, Zr3Sc4O12, and Zr3Yb4O12. Most of the compounds exhibit cation ordering, a situation observed previously only in UY6O12. One-seventh of the cations occupy a set of special sites of symmetry 3 and are octahedrally coordinated by oxygen. These cations are of the type that has the smallest available ionic radius. The remaining cations occupy a set of general sites randomly with respect to atom type and are sevenfold coordinated by oxygen. In Hf3Sc4O12, only partial ordering of this nature occurs, while it is confirmed that no cation ordering occurs in Zr3Sc4O12. Some aspects of the cation order-disorder situation are discussed.
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