SFCA-II type Ca2.46Fe3+8.57 Fe2+0.52Al5.45O24 – an improved structural model for an iron-ore sinter phase

Abstract Single crystals of SFCA-II with composition Ca 2.46 Fe 3+ 8.57 2+ 0.52 Al 5.45 O 24 have been obtained from synthesis experiments in the temperature range between 1300 and 1200 °C. Diffraction at ambient conditions yielded following basic crystallographic data: space group P $$ \overline{1} 1¯ , a = 10.3016(4) Å, b 10.4656(4) c 17.9553(6) α 90.062(3), β 89.977(3)°, γ 109.510(3)°, V 1824.66(12) Å 3 Z 4. Structure determination subsequent least-squares refinements resulted residual R(|F|) 0.0349 for 7406 independent reflections 773 parameters. Site occupancy on 35 octahedral (M) tetrahedral (T) positions asymmetric unit were aided by crystallochemical considerations assumption charge balance cations anions. The derived formula compares well outcome electron microprobe studies. crystal structure shows typical features SFCA-family. It can be built an alternating sequence two different types fundamental layers. For SFCA-II, they are oriented parallel to (100). Layer-type I is solely based [MO 6 ]-octahedra (M: Ca, Al) forming individual five polyhedra wide bands. Within single band, octahedra share common edges. II, other hand, contains as [TO 4 ]-tetrahedra (T: Al, ). By corner sharing each ]-group linked adjacent tetrahedra into [MT 2 12 ]-clusters or “winged octahedra”. Linkage neighboring strips these moieties provided additional arranged vierer single-chains. Our investigation rectifies previous studies where wrong atomic coordinates published.