High-temperature X-ray diffraction and Raman spectroscopy of diopside and pseudowollastonite

被引:124
作者
Richet, P
Mysen, BO
Ingrin, J
机构
[1] Inst Phys Globe, Lab Geomat, CNRS, URA 734, F-75252 Paris 05, France
[2] Carnegie Inst Washington, Geophys Lab, Washington, DC 20015 USA
[3] Carnegie Inst Washington, NSF, Ctr High Pressure Res, Washington, DC 20015 USA
[4] Univ Paris Sud, Lab Geophys & Geodynam Interne, CNRS, URA 1369, F-91405 Orsay, France
关键词
D O I
10.1007/s002690050130
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
Diopside(CaMESi2O6) and pseudowollastonite (CaSiO3) have been studied by X-ray powder diffraction and Raman spectroscopy up to their respective melting points. In agreement with previous unit-cell parameters determinations below 1100 K, thermal expansion of diopside along the a and c axis is much smaller than along the b axis. For pseudowollastonite, the axis expansivity increases slightly in the order b>a>c. For both minerals, the change in unit-cell angles is very small and there are no anomalous variations of the other unit-cell parameters near the melting point. With increasing temperatures, the main changes observed in the Raman spectra are strong increases of the linewidths for those bands which mainly represent Si-O-Si bending (near 600 cm(-1)) or involve 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 onset of calorimetric premelting effects, this extensive band widening results in a broad Raman feature that can no longer be deconvoluted into its individual components. No significant changes affect the Si-O streching modes. For both diopside and pseudowollastonite, premelting appears to be associated with enhanced dynamics of the alkaline-earth elements. This conclusion contrasts markedly with that drawn for sodium metasilicate in which weaker bonding of sodium allows the silicate framework to distort and deform in such a way as to prefigure the silicate entities present in the melt.
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页码:401 / 414
页数:14
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