An EXAFS study of Gd, Er and Lu site location in the epidote structure

Abstract

L III edge extended X-ray absorption fine structure (EXAFS) spectra of Gd, Er and Lu environments in synthetic epidotes of composition CaLa0.9 X 0.1Al2MgSi3O13H (X=Gd or Er or Lu) were recorded using synchrotron radiation. The Fourier transforms of the Gd-, Er- and Lu-EXAFS are clearly different from one another indicating wholly or partially different site occupancy. Model fitting of the Fourier-filtered partial EXAFS and comparison of pair distribution functions with those calculated for natural epidote leads to the conclusion that three different sites are probably involved in the accommodation of these elements in the epidote structure, and that site preference is a function of the rare earth ionic size. Gd is located in A2-type sites, whereas the local atomic environment of Er is consistent with A1 site occupancy and the Lu environment has been modelled on an M3-type octahedral site.