Rietveld refinement of the ranciéite structure using synchrotron powder diffraction data

Abstract

Rietveld refinement using synchrotron powder X-ray diffraction data of the ranciéite, Ca_0.19K_0.01(Mn⁴⁺_0.91◻_0.09)O₂⋅0.63H₂O, crystal structure reveals significant differences from that reported previously. The interlayer H₂O 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 H₂O molecules in the interlayer.