The OH site in topaz: an IR spectroscopic investigation |
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Authors: | Anke Watenphul Eugen Libowitzky Bernd Wunder Matthias Gottschalk |
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Institution: | 1. Deutsches GeoForschungsZentrum (GFZ), Section?3.3, Telegrafenberg, 14473, Potsdam, Germany 2. Institut für Mineralogie und Kristallographie, Universit?t Wien–Geozentrum, Althanstra?e 14, 1090, Wien, Austria
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Abstract: | The OH site in topaz is investigated by IR spectroscopy depending on the OH concentration and temperature. The two OH bands
that can be distinguished are due to the local ordering of F and OH in opposite sites of the crystal structure. The first
typical sharp band stems from OH groups with fluorine in the opposite (=acceptor) site. The second band occurs as a shoulder
on the low-energy wing and is related to two opposite OH groups. The degree of local OH–OH ordering depends on the OH concentration
and, due to statistical F/OH distribution, can be predicted by probability calculations. The substitution of OH for F has
a non-linear effect on the increase of the lattice parameters. An autocorrelation analysis of the IR spectra revealed two
temperature-induced phase transitions. At −135°C, the local symmetry changes from P1 to Pbn21, although this change involves only the H atoms. The transition from Pbn21 to Pbnm at 160°C is caused by changes of the local F/OH ordering in the crystal structure. |
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