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

During our research on alkali-fluorides, the compound NaSrMg2F7 has been pr epared by a precipitation reaction of Sr2+, Mg2+ and Na+ with F- for the fi rst time. The powder crystallizes as a single phase in the form of spherica l 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, spectroscopica l investigations confirm the presence of two coupled fluoride ions. The cry stal structure corresponds to the pyrochlore structure type A(2)B(2)X(7) Wi th 50% occupation of Sr2+ or Na+ at the A site.