EXAFS determination of local atomic structure of selected transition metals in CdSe matrix

The EXAFS analysis of the K-edges of the selected transition metals (Mn, Fe , Co) admired to CdSe matrix was performed. The bond lengths between these transitions metals and selenium atom were determined. The following values were found: Mn (2.544 Angstrom); Fe (2.498 Angstrom); Co (2.43 Angstrom) wi th the accuracy of 0.01 Angstrom, This enabled us to estimate the tetrahedr al covalent radii for the transition metals studied and to make a qualitati ve comparative analysis with the analogous EXAFS data obtained for the same transition metals in ZnS. Covalent radii of considered metals in the much heavier CdSe matrix show the same tendency of decreasing with filling of th e 3d orbit as in ZnS matrix. However we found these radii systematically la rger in CdSe than in ZnS matrix. This fact indicates a decrease in the cati on valence electron localisation in the presence of much heavier Se anion c omparing to the S anion and therefore an increase in bond ionicity. (C) 199 9 Elsevier Science S.A. All rights reserved.