Synthesis and structural characterization of a new yttrium phosphate: Na2.5Y0.5Mg7(PO4)6 with fillowite-type structure

A new phosphate, Na2.5Y0.5Mg7(PO4)6 was synthesized as single crystals by the flux method and as a powdered sample by the Pechini technique, and investigated by single crystal X-ray diffraction, charge distribution (CD) and 31P NMR spectroscopy. This compound crystallized in the rhombohedral space group R and its equivalent hexagonal cell had the following parameters: a=1.4976(6) nm, c= 4.2599(7) nm, Z= 18. The structure consisted of MgO5, MgO6, YO6, (Na,Y)O8 and NaOx (x=6, 7 and 9) polyhedra which were linked either directly through common corners, edges and faces and by means of the PO4 tetrahedra via common corners and edges, giving rise to a complex three-dimensional framework, similar to that of the fillowite-like structure. The cation distribution was confirmed by charge distribution (CD) calculations and 31P NMR spectroscopy study.