Cd-SUBSTITUTED GOETHITES - A STRUCTURAL INVESTIGATION BY SYNCHROTRON X-RAY DIFFRACTION

摘要

The structural and physical effects of partially substituting Cd for Fe in goethite have been investigated. The solubility of Cd~(2+) in goethite is ～10 mol.%, i.e. Fe_(0.905)Cd_(0.095)OOH. The structures of the substituted goethites have been refined, using the Rietveld method, from synchrotron X-ray powder diffraction data. There is a progressive increase in the size of the unit-cell parameters and unit-cell volume, upon the incorporation of much larger Cd~(2+) ion (0.95 A) compared with Fe~(3+) (0.645 A) in the goethite structure, together with a reduction in crystallinity. Transmission electron microscopy measurements confirm the crystallite size decreases as the Cd~(2+) content increases in goethite structure.