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

Autor(en)

Eugen Libowitzky, George R. Rossman

Abstrakt

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 mols. are confirmed by the energies of the OH stretching fundamentals around 3350-3600 cm-1. However, even though 2 O-H stretching bands in both a and c are predicted by factor group anal., 3 strong bands in a, and 2 in c are obsd. 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 mols. and OH groups within the structural channels. These motions can be partly explained by a twisting motion of the water mol. around its 2-fold mol. axis. A better interpretation is found in dynamic proton disorder, which describes a hopping motion between disordered proton sites. A possible dynamic disorder-order phase transition at low temps. was tested by detn. of birefringence values (Dn) of hemimorphite between 82 and 373 K. A strong discontinuity in the slope of DnX,Y and DnY,Z was obsd. at 98(2) K. This, together with considerable energy shifts of IR bands upon cooling, provides evidence for a low-temp. second-order phase transition in hemimorphite.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

California Institute of Technology (Caltech)

Journal

European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences

Band

9

Seiten

793-802

Anzahl der Seiten

10

ISSN

0935-1221

DOI

https://doi.org/10.1127/ejm/9/4/0793

Publikationsdatum

08-1997

Peer-reviewed

Ja

ÖFOS 2012

105113 Kristallographie, 105116 Mineralogie, 104026 Spektroskopie

Schlagwörter

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/ir-spectroscopy-of-hemimorphite-between-82-and-373-k-and-optical-evidence-for-a-lowtemperature-phase-transition(81250265-407b-4853-af85-315e728f9160).html