Rietveld refinement of the ranciéite structure using synchrotron powder diffraction data

Rietveld refinement using synchrotron powder X-ray diffraction data of the ranciéite, Ca 0.19 K 0.01 (Mn 4+ 0.91 ◻ 0.09 )O 2 ⋅0.63H 2 O, crystal structure reveals significant differences from that reported previously. The interlayer H 2 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 (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 2 O molecules in the interlayer.