Determination of the cation distribution in Fe2Ni(PO4)2using isotopic substitution and powder neutron diffraction

Abstract

The distribution of divalent iron and nickel over the two metal sites with differing coordination geometry in Fe2Ni(PO4)2, sarcopside, has been investigated using time-of-flight powder neutron diffraction of nickel isotopically substituted materials. Data from four separate samples were collected using HRPD at ISIS, containingnatNi,58Ni,60Ni and62Ni, under identical conditions. The occupancy of iron on theM(1) site was found to be 0.290 (1) from a combined-data-set Rietveld refinement of the three isotopically substituted samples, compared with 0.26 (4) and 0.26 (15) respectively from this and a previous time-of-flight powder neutron diffraction study using natural-abundance nickel, and 0.366 (6) and 0.376 (3) using anomalous X-ray scattering techniques. A critical comparison of isotope substitution neutron diffraction and anomalous X-ray scattering methods for distinguishing nickel and iron from powder data is presented.