RIETVELD REFINEMENT OF THE KAOLINITE STRUCTURE AT 1.5-K
RIETVELD REFINEMENT OF THE KAOLINITE STRUCTURE AT 1.5-K
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DOI：
10.1346/ccmn.1993.0410613
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发表时间：
1993-12-01
影响因子：
2.2
通讯作者：
BISH, DL
中科院分区：
文献类型：
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作者：
BISH, DL
Keokuk高岭石的晶体结构，包括所有的H原子，使用低温（1.5 K）中子粉末衍射数据（λ = 1.9102埃）和Rietveld细化/差分傅立叶方法在空间群C1中细化到R（wp）= 1.78%，约化的chi 2 = 3.32。单元格参数为：a = 5.1535（3）埃，B = 8.9419（5）埃，c = 7.3906（4）埃，α = 91.926（2）度，β = 105.046（2）度，γ = 89.797（2）度，V = 328.70（5）埃3。晶胞参数表明，大部分的热收缩发生沿着[001]方向，显然是由于在层间距离的减少。考虑到数据收集的低温，非H结构与已发表的Cl结构非常相似，但H原子的位置不同。内部OH基团基本上在层的平面中，并且内表面OH基团与（00 1）平面成60度-73度的角。差分傅立叶图显示在[001]方向的内部OH基团的较小的各向异性，但内表面OH基团似乎有其最大的振动（或位置无序）平行于层的组件。虽然没有数据表明高岭石中的任何H位点的分裂位置，但存在对H原子的有限随机位置无序的支持。然而，这些数据没有提供支持的空间群对称性低于Cl。
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 (lambda = 1.9102 angstrom) and Rietveld refinement/difference-Fourier methods to R(wp) = 1.78%, reduced chi2 = 3.32. Unit-cell parameters are: a = 5.1535(3) angstrom, b = 8.9419(5) angstrom, c = 7.3906(4) angstrom, alpha = 91.926(2)-degrees, beta = 105.046(2)-degrees, gamma = 89.797(2)-degrees, and V = 328.70(5) angstrom3. 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 Cl 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-degrees-73-degrees with the (00 1) 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 Cl.