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Rietveld Refinement of the Kaolinite Structure at 1.5 K

Published online by Cambridge University Press:  28 February 2024

David L. Bish
David L. Bish*
Affiliation:
Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, Mexico 87545
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Abstract

The crystal structure of Keokuk kaolinite, including all H atoms, was refined in space group C1 using low-temperature (1.5 K) neutron powder diffraction data (λ = 1.9102 Å) and Rietveld refinement/difference-Fourier methods to Rwp = 1.78%, reduced χ2 = 3.32. Unit-cell parameters are: a = 5.1535(3) Å, b = 8.9419(5) Å, c = 7.3906(4) Å, α = 91.926(2)°, β = 105.046(2)°, γ = 89.797(2)°, and V = 328.70(5) Å3. Unit-cell parameters show that most of the thermal contraction occurred along the [001] direction, apparently due to a decrease in the interlayer distance. The non-H structure is very similar to published C1 structures, considering the low temperature of data collection, but the H atom positions are distinct. The inner OH group is essentially in the plane of the layers, and the inner-surface OH groups make angles of 60°–73° with the (001) plane. Difference-Fourier maps show minor anisotropy of the inner-OH group in the [001] direction, but the inner-surface OH groups appear to have their largest vibrational (or positional disorder) component parallel to the layers. Although no data indicate a split position of any of the H sites in kaolinite, there is support for limited random positional disorder of the H atoms. However, these data provided no support for a space group symmetry lower than C1.

Keywords

Crystal structureH positionsKaoliniteLow temperatureNeutron powder diffractionRietveld refinement
Type
Research Article
Information
Clays and Clay Minerals , Volume 41 , Issue 6 , December 1993 , pp. 738 - 744
Copyright
Copyright © 1993, The Clay Minerals Society

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