Abstract--The crystal structure of a deuterated synthetic boehmite powder, "y-A1OOD, has been determined by time-of-flight neutron diffraction and Rietveld profile refinement in space group Cmcm to a weighted profile R of 3.71%. Cell dimensions are a = 2.868(1), b = 12.2336(4), and c = 3.6923(1) /~. Alternate space groups for the boehmite structure suggested in the recent literature were found to be unacceptable. Atom positions, bond distances, and angles, with the exception of those involving hydrogen, were nearly identical to those determined by R. J. Hill in 1981 who studied a single crystal of boehmite by X-ray diffraction. All atoms were refined with anisotropic thermal parameters. The b value is 0.013 larger, and the thermal ellipsoids of oxygen are slightly more anisotropic than those reported by Hill and may reflect the different samples studied.

Abstract--The crystal structure of a synthetic boehmite sample has been refined to an R of 0.047 in the space group Amam from X-ray powder diffraction data. Inclusion of hydrogen atoms and/or refinement in the space group A21am gave poorer results. Cell dimensions were determined as a = 3.6936 (_+ 0.0003), b = 12.214 (-+ 0.001), c = 2.8679 (_+ 0.0003) ~,. All AI-O(OH) distances lie between 1.88 and 1.91/~. Shared octahedral edges are 2.51-2.52/~, and unshared octahedral edges are 2.86-2.87/~, in excellent agreement with those for layered silicates. The O-H... O distance between contiguous octahedral sheets is 2.71/~. The computed X-ray pattern matches closely with the experimental pattern, indicating the degree to which the crystal structure has been determined.

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