title: Rietveld refinement of whitlockite-related K(0.8)Ca(9.8)Fe(0.2)(PO(4))(7).
abstract: The title compound, K(0.8)Ca(9.8)Fe(0.2)(PO(4))(7) (potassium deca-calcium iron hepta-phosphate), belongs to the whitlockite family. The structure is built up from several types of metal-oxygen polyhedra: two [CaO(8)], one [CaO(7)] and one [(Ca/Fe)O(6)] polyhedron with a mixed Ca/Fe occupancy in a 0.8:0.2 ratio, as well as three tetra-hedral [PO(4)] units. Of the 18 sites in the asymmetric unit, the site with the mixed Ca/Fe occupation, the K site, one P and one O site are on special positions 6a with 3 symmetry, whereas all other sites are on general positions 18b. The linkage of metal-oxygen polyhedra and [PO(4)] tetra-hedra via edges and corners results in formation of a three-dimensional framework with composition [Ca(9.8)Fe(0.2)(PO(4))(7)](0.8-). The remaining K atoms (site-occupation factor = 0.8) are located in large closed cavities and are nine-coordinated by oxygen.
authors.affiliation: Department of Inorganic Chemistry, Taras Shevchenko National University, 64 Volodymyrska str., 01601 Kyiv, Ukraine.
authors.forename: Igor V
authors.initials: IV
authors.lastname: Zatovsky
authors.forename: Ivan V
authors.initials: IV
authors.lastname: Ogorodnyk
authors.forename: Nataliya Yu
authors.initials: NY
authors.lastname: Strutynska
authors.forename: Nikolay S
authors.initials: NS
authors.lastname: Slobodyanik
authors.forename: Nataliya O
authors.initials: NO
authors.lastname: Sharkina