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Propriétés électroniques et structurales du chrome en impureté dans les cristaux. Approche expérimentale et théorique.

Abstract : The aim of the thesis is to study the electronic and structural environment of chromium substituting for aluminium in insulating cubic crystals, and to discuss its influence on the variation of the crystal field. We have combined spectroscopies, which are selective of chromium (EXAFS and XANES at the Cr K-edge), ab initio calculations (energy minimization and computation of XANES spectra) and multielectronic calculations (simulation of X-ray linear dichroism). Theoretical developments have been performed and applied to the case of the x-ray absorption cross-section, in order to extract the spectroscopic properties of a single substitutional site from those of the cubic crystal.

The relaxed structural environment around chromium has been determined in spinel MgAl2O4:Cr3+ (red), pyrope garnet Mg3Al2Si3O12:Cr3+ (red) and grossular garnet Ca3Al2Si3O12:Cr3+ (green). The coordination sphere of Cr is similar to that observed in the corresponding end-member (MgCr2O4, Mg3Cr2Si3O12 et Ca3Cr2Si3O12, respectively), concerning the interatomic distances and the local symetry. The variation of the mean Cr-O distance plays a significant role in that of the crystal field, but fails to explain by itself the crystal field differences along solid solutions, between dilute crystals or between concentrated crystals. We show that the nature of the Cr-O chemical bond is a relevant factor and that the medium range environment around chromium has an influence on its spectroscopic properties. In particular, the second neighbours have an influence on the Cr-O distance and on the nature of the chemical bond.
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https://tel.archives-ouvertes.fr/tel-00340612
Contributor : Amélie Juhin <>
Submitted on : Friday, November 21, 2008 - 2:07:40 PM
Last modification on : Tuesday, December 8, 2020 - 3:40:41 AM
Long-term archiving on: : Monday, June 7, 2010 - 9:50:32 PM

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  • HAL Id : tel-00340612, version 1

Citation

Amélie Juhin. Propriétés électroniques et structurales du chrome en impureté dans les cristaux. Approche expérimentale et théorique.. Matériaux. Université Pierre et Marie Curie - Paris VI, 2008. Français. ⟨tel-00340612⟩

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