Abstract
Synthesis and structure of two phosphates belonging to the ternary Sb2O5-Fe2O3-P2O5system are reported. Structures of both SbV1.50FeIII0.50(PO4)3and (SbV0.50FeIIIe0.50)P2O7phases, obtained by solid state reaction in air atmosphere at 950 °C and 900 °C, respectively, were determined at room temperature from X-ray powder diffraction using the Rietveld method. Sb1.50Fe0.50(PO4)3phosphate belongs to the Nasicon-type structure withR32 space group. Hexagonal cell parameters areahex.=8.305(1) Å andchex.=22.035(2) Å. Rietveld refinement results show a 2-2 ordered distribution, along thec-axis, ofX(1) andX(2) sites (crystallographic formula [Sb0.88Fe0.12]X(1)[Fe0.38Sb0.62]X(2)(PO4)3) in the Nasicon framework. (Sb0.50Fe0.50)P2O7is isotypic withβ-SbP2O7pyrophosphate [Pna21space group;a=7.865(1) Å,b=15.699(2) Å,c=7.847(1) Å]. Its crystal structure is built up from corner-shared SbO6or FeO6octahedra and P2O7groups (two group types). Each P2O7group shares its six vertices with three SbO6and three FeO6octahedra, and each octahedra is connected to six P2O7groups. A quasi 1-1 ordered distribution, along theb-axis, of Sb5+and Fe3+ions in the pyrophosphate framework are observed.
Published Version
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