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IR spectroscopy of hemimorphite between 82 and 373 K and optical evidence for a low-temperature phase transition

Libowitzky, Eugen and Rossman, George R. (1997) IR spectroscopy of hemimorphite between 82 and 373 K and optical evidence for a low-temperature phase transition. European Journal of Mineralogy, 9 (4). pp. 793-802. ISSN 0935-1221.

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Polarized IR absorption spectra of oriented hemimorphite single-crystals were recorded in the region of the O-H fundamentals and combination bands between 82 and 373 K. The almost exclusive orientation of the absorption bands in the (010) plane is in agreement with previous neutron structure refinements. The weak H bonds of the OH groups and water molecules are confirmed by the energies of the OH stretching fundamentals around 3350-3600 cm^(-1). However, even though two O-H stretching bands in both ɑ and c are predicted by factor group analysis, three strong bands in ɑ, and two in c are observed. This fact, as well as the occurrence of weak satellite bands in the a and c spectra, and a minor component parallel to the b axis direction, indicate complicated dynamics of the water molecules and OH groups within the structural channels. These motions can be partly explained by a twisting motion of the water molecule around its two-fold molecular axis. A much better interpretation for these motions, however, is found in dynamic proton disorder, which describes a hopping motion between disordered proton sites. A possible dynamic disorder-order phase transition at low temperatures was tested by determination of birefringence values (Δn) of hemimorphite between 82 and 373 K. A strong discontinuity in the slope of Δn_(x,γ) and Δn_(γ,z) was observed at 98(2) K. This, together with considerable energy shifts of IR bands upon cooling, provides evidence for a low-temperature second-order phase transition in hemimorphite.

Item Type:Article
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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1997 E. Schweizerbart'sche Verlagsbuchhandlung. Received 22 March 1996. Accepted 10 February 1997. T. Armbruster (Bern) helped with crystallographic literature, and RJ. Wyllie (Caltech) made his cold-seal vessels available for this study. J. Winkler (Caltech) assisted with the Raman measurements. E.L. acknowledges financial support from the "Fonds zur Förderung der wissenschaftlichen Forschung, Austria" during an "Erwin-Schrödinger" fellowship, project J01098-GEO. G.R.R. acknowledges support from the National Science Foundation, grant EAR 9218980. The comments of referees K. Langer (Berlin) and A. Eriksson (Uppsala) helped to improve the quality of the manuscript.
Group:UNSPECIFIED, UNSPECIFIED, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Fonds zur Förderung der wissenschaftlichen ForschungUNSPECIFIED
Erwin-Schrödinger FellowshipJ01098-GEO
NSFEAR 9218980
Subject Keywords:hemimorphite, infrared spectroscopy, water, hydroxide, phase transition.
Issue or Number:4
Record Number:CaltechAUTHORS:20130501-145714272
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Official Citation: Eugen Libowitzky and George R. Rossman IR spectroscopy of hemimorphite between 82 and 373 K and optical evidence for a low-temperature phase transition Eur J Mineral, August 1997, v. 9, p. 793-802
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38217
Deposited By: Ruth Sustaita
Deposited On:01 May 2013 22:37
Last Modified:03 Oct 2019 04:55

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