Neutron and X-ray total scattering study of hydrogen disorder in fully hydrated hydrogrossular, Ca3Al2(O4H4)3
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The structure of fully hydrated grossular, or katoite, contains an unusual arrangement of four O–H bonds within each O4 tetrahedra. Neutron and X-ray total scattering from a powdered deuterated sample have been measured to investigate the local arrangement of this O4D4 cluster. The O–D bond length determined directly from the pair distribution function is 0.954 Å, although the Rietveld-refined distance between average O and D positions was slightly smaller. Reverse Monte Carlo refinement of supercell models to the total scattering data show that other than the consequences of this correctly determined O–D bond length, there is little to suggest that the O4D4 structure is locally significantly different from that expected based on the average structure determined solely from Bragg diffraction.
KeywordsKatoite Neutron diffraction X-ray diffraction Pair distribution function Total scattering
TDB thanks the Royal Society and Trinity Hall (University of Cambridge) for funding. DAK is grateful to George Lager for pointing out the interest in fully characterizing the O4D4 structure in katoite. This work was carried out with the support of the Diamond Light Source (proposal EE15676).
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