Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure

J. Phys. IV France 7 (1997) C2-1157-C2-1158
DOI: 10.1051/jp4:19972171

Temperature Dependence of Disorder and Correlation Effets in the Almandine X-Site

S. Quartieri¹, G. Antonioli², G. Artioli³, C.A. Geiger⁴ and P.P. Lottici<sup>2

1</sup>  Dipartimento di Scienze della Terra, Via S. Eufemia 19, 41100 Modena, Italy
²  INFM and Dipartimento di Fisica, Viale delle Scienze, 43100, Parma, Italy
³  Dipartimento di Scienze della Terra, Via Botticelli 23, 20133 Milano, Italy
⁴  Mineralogisch-Petrographisches Institut, Olshausenstr. 40, 24098 Kiel, Germany

Abstract
XAFS measurements in the temperature range 20-473 K at the Fe K-edge of synthetic almandine (Fe₃Al₂Si₃O₁₂) allow us to determine the T-dependence of the XAFS Debye-Waller (DW) factors for each of the two crystallographically independent Fe-O bond distances (Fe(1)-O and Fe(2)-O). The XAFS DW factor of the longer Fe(2)-O bond is larger and has a greater T-dependence than the shorter Fe(l)-O bond, which remains constant over the measured T range. The XAFS DW factors are compared with the uncorrelated part of the DW factors derived from a single-crystal X-ray diffraction (XRD) studiy on almandine and are interpreted on the basis of the Einstein model. A comparison with diffraction data shows that the shorter Fe(1)-O bond is significantly affected by correlation in the atomic displacements.

© EDP Sciences 1997