X-Ray photoelectron diffraction studies of the micas lepidolite and biotite
| Autor: | Anthony G. Hiorns, Lynne A. Ash, Stephanie L. Clark, Stephen D. Evans |
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| Rok vydání: | 1988 |
| Předmět: | |
| Zdroj: | Journal of the Chemical Society, Dalton Transactions. :859 |
| ISSN: | 1364-5447 0300-9246 |
| DOI: | 10.1039/dt9880000859 |
| Popis: | Comprehensive X-ray photoelectron diffraction (x.p.d.) data for a Norwegian 1 M lepidolite and a 1 M biotite are reported and discussed. Improved techniques for the collection and processing of x.p.d. patterns are described, including a new procedure for correcting for the variation of instrumental response with the electron take-off angle. Comparison of x.p.d. patterns from rotation about near-equivalent axes at 120° to each other reveals that two major features in the interlayer ion patterns cannot be attributed to scattering by atoms nearer than 10–13 A from the emitting site. Enhanced anisotropy in the Rb 3d patterns relative to those for K 2p is discussed. It is shown that x.p.d. experiments involving polar rotations about an axis parallel to the unit-cell vector a can be used to detect octahedral cation ordering involving differentiation of the two sites with cis-OH groups; a similar method for detecting tetrahedral cation ordering is suggested. Rotation about axes at 120° to a is valuable for the identification of elements segregating equally into the two cis octahedral sites, while experiments involving rotation about axes parallel to and at 120° to the unit-cell vector b enable octahedral cation ordering amongst all three octahedral sites to be characterised. By these means octahedral Li and Mn in the lepidolite are shown to be concentrated in the trans M(1) site, and Al in M(3)(one of the two cis sites equivalent in C2/m symmetry). This mica thus has only C2 symmetry. The 1.2% of Ti in the biotite is segregated uniformly into the two cis octahedral sites, unlike the Mg and Fe which are distributed randomly amongst all three octahedral sites. Tetrahedral ordering was not detected in either mica. |
| Databáze: | OpenAIRE |
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