Rietveld refinement of the ranciéite structure using synchrotron powder diffraction data

Rietveld refinement using synchrotron powder X-ray diffraction data of the rancíite, Ca0.19 K0.01 (Mn 4+ 0.91 0.09) O2 0.63 H2 O, crystal structure reveals significant differences from that reported previously. The interlayer H2 O molecules occupy sites halfway between the Mn,O octahedral sheets. The Mn sites in the octahedral sheets have 10% vacancies, and the mean Mn-O distance indicates that all Mn is tetravalent (Mn4+). The interlayer Ca cations are located above and below the Mn vacancies and are octahedrally coordinated to three O2 atoms in the octahedral sheet and three H2 O molecules in the interlayer.