Vibrational spectroscopy of phase transitions in leonite-type minerals

Autor(en)

Birgit Hertweck, Eugen Libowitzky

Abstrakt

Infrared (IR) and Raman spectra of leonite-type minerals, K2Me(SO4)2·4H2O (Me = Mg, Mn, Fe), confirm a succession of structural phase transitions between 277 and 120 K. Because the orientation and dynamic behaviour of the sulphate tetrahedra undergo the most conspicuous changes during these transitions, transmission IR and Raman spectra were recorded for the SO4 bending and stretching modes from 660 to 1230 cm-1 (IR) and 350 to 1250 cm-1 (Raman), in a temperature range between 80 K and room temperature.

At low temperature the leonite-type minerals show an order-disorder phase transition due to the freezing of the dynamic sulphate disorder. These phase transitions are characterised by non-linear shifts of the peak positions as a function of temperature in IR and Raman spectra. Evaluation of the peak widths of the sulphate modes in the IR and Raman spectra by autocorrelation analysis show non-linear decreases of the width parameters, confirming a tricritical ordering process according to the Landau order parameter. With decreasing temperature the crystal structures of the Mg- and Mn-endmembers switch to another ordered phase. These structural changes are accompanied by the sudden appearance of additional sulphate stretching and bending modes and by discontinuities of the peak shifts in IR and Raman spectra, indicating a first order phase transition.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Universität Wien

Journal

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

Band

14

Seiten

1009-1017

Anzahl der Seiten

9

ISSN

0935-1221

DOI

https://doi.org/10.1127/0935-1221/2002/0014-1009

Publikationsdatum

2002

Peer-reviewed

Ja

ÖFOS 2012

1051 Geologie, Mineralogie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/16005871-687f-458a-8331-fab83b2e30bf