Synchrotron X-ray and TOF neutron powder diffraction study of a lyonsite-type oxide Co3.6Fe3.6(VO4)6

Abstract

Co 3.6 Fe 3.6 (VO 4 ) 6 was synthesized by solid-state reaction at 900 °C, and its structure was determined by X-ray and neutron powder diffraction. Co 3.6 Fe 3.6 (VO 4 ) 6 is isotypic with lyonsite (space group: Pnma; Z =2), having lattice parameters of a =4.96480(9) Å, b =10.2245(2) Å, and c =17.2100(3) Å. Its structure parameters were refined by the Rietveld method with two sets of synchrotron X-ray (wavelengths: 0.85001 and 1.74500 Å) and time-of-flight neutron powder diffraction data. Co 2+ and Fe 3+ ions are distributed among three different metal sites M 1– M 3. Not Co 2+ ions but Fe 3+ ions are mainly contained in face-sharing M 3O 6 octahedra, forming single chains parallel to the [1 0 0] direction. Edge- and corner-sharing octahedra M 2O 6 build up layers perpendicular to the [0 0 1] direction. Edge-sharing trigonal prisms M 1O 6 form zig-zag single chains along the [1 0 0] direction. The M 1 and M 3 sites are about 6.0(2)% and 34.0(2)% deficient, respectively. The tendency for Co 2+ and Fe 3+ ions to distribute among the three metal sites is discussed on the basis of the electrostatic valence rule. Graphic