Structural relaxation around substitutional Cr3+ in pyrope garnet

Amélie Juhin (1) , Georges Calas (1) , Delphine Cabaret (1) , Laurence Galoisy (1) , Jean-Louis Hazemann (2)

1 IMPMC - Institut de minéralogie et de physique des milieux condensés
2 NEEL - MRS - Matériaux, Rayonnements, Structure

The structural environment of substitutional Cr3+ ion in a natural pyrope Mg3Al2Si3O12 has been investigated by Cr K-edge Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) coupled with first-principles computations. The Cr-O distance is close to that in knorringite Mg3Cr2Si3O12, indicating a full relaxation of the first neighbors. The local C3i symmetry of the octahedral Y site is retained during Cr-Al substitution. The second and third shells of neighbors (Mg and Si) relax only partially. Site relaxation is accommodated by strain-induced bond buckling, with angular tilts of the Si-centered tetrahedra around the Cr-centered octahedron, and by a radial deformation of the Mg-centered dodecahedra.

Mots clés: Cr-pyrope; relaxation; XAS; ab initio

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Amélie Juhin, Georges Calas, Delphine Cabaret, Laurence Galoisy, Jean-Louis Hazemann. Structural relaxation around substitutional Cr3+ in pyrope garnet. The American Mineralogist, 2008, 93 (5-6), pp.800-805. ⟨10.2138/am.2008.2823⟩. ⟨hal-00181015⟩