HIGH-TEMPERATURE X-RAY-DIFFRACTION AND RAMAN-SPECTROSCOPY OF DIOPSIDEAND PSEUDOWOLLASTONITE

Citation
P. Richet et al., HIGH-TEMPERATURE X-RAY-DIFFRACTION AND RAMAN-SPECTROSCOPY OF DIOPSIDEAND PSEUDOWOLLASTONITE, Physics and chemistry of minerals, 25(6), 1998, pp. 401-414
Citations number
45
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Mineralogy,"Material Science
ISSN journal
0342-1791
Volume
25
Issue
6
Year of publication
1998
Pages
401 - 414
Database
ISI
SICI code
0342-1791(1998)25:6<401:HXAROD>2.0.ZU;2-P
Abstract
Diopside(CaMESi2O6) and pseudowollastonite (CaSiO3) have been studied by X-ray powder diffraction and Raman spectroscopy up to their respect ive melting points. In agreement with previous unit-cell parameters de terminations below 1100 K, thermal expansion of diopside along the a a nd c axis is much smaller than along the b axis. For pseudowollastonit e, the axis expansivity increases slightly in the order b>a>c. For bot h minerals, the change in unit-cell angles is very small and there are no anomalous variations of the other unit-cell parameters near the me lting point. With increasing temperatures, the main changes observed i n the Raman spectra are strong increases of the linewidths for those b ands which mainly represent Si-O-Si bending (near 600 cm(-1)) or invol ve Ca-O or Mg-O stretching, in the range 270-500 cm(-1) for diopside, and 240-450 cm(-1) for pseudowollastonite. At temperatures near the on set of calorimetric premelting effects, this extensive band widening r esults in a broad Raman feature that can no longer be deconvoluted int o its individual components. No significant changes affect the Si-O st reching modes. For both diopside and pseudowollastonite, premelting ap pears to be associated with enhanced dynamics of the alkaline-earth el ements. This conclusion contrasts markedly with that drawn for sodium metasilicate in which weaker bonding of sodium allows the silicate fra mework to distort and deform in such a way as to prefigure the silicat e entities present in the melt.