Synthesis and crystal structure analysis of NaSrMg2F7, a fully fluorinated compound of the pyrochlore family

During our research on alkali-fluorides, the compound NaSrMg2F7 has been prepared by a precipitation reaction of Sr2+, Mg2+ and Na+ with F- for the first time. The powder crystallizes as a single phase in the form of spherical agglomerates similar to0.25 mum in diameter. The compound crystallizes in the space group Fd (3) over barm (Nr.227) with lattice parameter a10.4379(4) Angstrom. Structural analysis by the Rietveld method was done from X-ray diffraction data. In agreement with the structure analysis, spectroscopical investigations confirm the presence of two coupled fluoride ions. The crystal structure corresponds to the pyrochlore structure type A(2)B(2)X(7) With 50% occupation of Sr2+ or Na+ at the A site.