Rietveld refinement of the rancieite structure using synchrotron powder diffraction data

摘要

Rietveld refinement using synchrotron powder X-ray diffraction data of the rancieite, Ca_(0.19)K_(0.01)(Mn_(0.09)~(4+)□_(0.09))O_2·0.63H_2O, crystal structure reveals significant differences from that reported previously. The interlayer H_2O 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 (Mn~(4+)). The interlayer Ca cations are located above and below the Mn vacancies and are octahedrally coordinated to three O_2 atoms in the octahedral sheet and three H_2O molecules in the interlayer.