Neutron and X-ray total scattering study of hydrogen disorder in fully hydrated hydrogrossular, Ca3Al2(O4H4)3.

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. [ABSTRACT FROM AUTHOR]