TEMPERATURE-DEPENDENCE OF DISORDER AND CORRELATION-EFFECTS IN THE ALMANDINE X-SITE

XAFS measurements in the temperature range 20-473 It at the Fe K-edge of synthetic almandine (Fe3Al2Si3O12) allow us to determine the T-depe ndence of the XAFS Debye-Waller (DW) factors for each of the two cryst allographically independent Fe-O bond distances (Fe(1)-O and Te(2)-O). The XAFS DW factor of the longer Fe(2)-O bond is larger and has a gre ater T-dependence than the shorter Fe(1)-O bond, which remains constan t 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-r ay diffraction (XRD) studiy on almandine and are interpreted on the ba sis of the Einstein model. A comparison with diffraction data shows th at the shorter Fe(1)-O bond is significantly affected by correlation i n the atomic displacements.