The binary systems SrF2-RF3with R ≡ La - Nd, Sm - Lu, and Y were investigated systematically for the appearance of an intermediate phase with composition Sr2RF7. As a result of this study, we have discovered that this type of compound exists only for R ≡ Sm - Lu and Y. For R ≡ La - Nd, either the corresponding disordered solid solution with anion-excess fluorite (cα) was found, or a diphasic mixture of cα and other intermediate phases with compositions richer in RF3. Guinier X-ray powder diffraction was used for the structural characterization of all phases. Additionally, electron diffraction from single crystals was carried out for Sr2RF7phases with R ≡ Sm, Gd, Tb, Er, Yb, Y. For all Sr2RF7phases, a tetragonal fluorite-related superstructure was established with as= 0.5(10)1 2aF, cs= 3aF, Z = 30, space group I4/m. This superstructure type t is the same as in the case of Ca2RF7phases, but different from Ba2RF7(t') where only partial ordering occurs one-dimensionally along the z axis. © 1986.
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