Abstract--The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRE Grenoble, France (X = 0.6883, T -room temperatu[e). The volume of the crystals was 8 and 0.8 txm 3, respectively. Unit-cell parameters are: a = 5.154(9) A, b = 8.942(4) A, c = 7.401(10) A, c~ ~ 91.69(9) ~ , 13 = 104.61(5) ~ "/ -89.82(4) ~ . Space group C1 is consistent with the observed data. All non-hydrogen atoms were independently refined with anisotropic displacement parameters. The positions and isotropic displacement parameters for the three interlayer H atoms were refined a/so. The position of the intralayer H was found by difference-Fourier methods, although refinement was not possible. Difference-Fourier maps suggested large anisotropic displacement vectors of this intralayer H, however, no evidence for a second maximum was found. The diffraction patterns show diffuse scattering in streaks parallel to [001]* through hkl reflections with hk 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.
transition with change of space group symmetry, and the systematic reanangement of T-0-T bonds in the high-temperature phase, To our knowledge, this is the first direct experimental evidence of a zeolite framework disruption dming dehydration caused by increased cation coordination to framework oxygens,
We developed a small vacuum chamber for very low background single crystal diffraction experiments. The chamber has been designed for a large Eulerian cradle. The
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