THE EFFECT OF UNEQUAL DISTANCE COORDINATION IN A STANDARD SAMPLE ON EXAFS DATA-ANALYSIS

The authors investigate the effect of unequal distance coordination in a standard sample on EXAFS data analysis, particularly on structural results from a curve fitting procedure. They calculate analytically this effect for a simple model, and EXAFS spectra of rutile type GeO2, alpha -quartz type GeO2, Fe3O4 and LaFeO3 are measured to demonstrate this effect experimentally. A simulation computation is also carried out. The results show that the sample in which the neighbouring atoms around the absorbing one form two coordination subshells, can be used as a standard only if the differences of interatomic distances and mean square radial displacements between these two subshells are less than 0.1 AA and 0.0015 AA2 respectively. A simple and feasible method is developed to eliminate this effect quantitatively for accurate structural determination. Improvement of accuracy of results based on this method is obtained. The situation about this effect for a complex model is discussed.