THE STRUCTURE OF AMORPHOUS COPPER SULFIDE PRECIPITATES - AN X-RAY-ABSORPTION STUDY

X-ray absorption (XAS) and X-ray photoelectron spectroscopy (XPS) anal ysis of copper sulfide precipitated from aqueous solution at ambient t emperatures reveals the existence of a metastable primitive structure that ages to a structure with the characteristics of amorphous covelli te; XAS provides direct structural information on the structure of the se amorphous copper sulfides. Extended X-ray absorption fine structure (EXAFS) analysis of the primitive structure demonstrates the presence of disulfide (S-2-groups) and a Cu-S interaction of 2.8 Angstrom: the latter is not found in covellite. Copper K-edge X-ray absorption near -edge structure (XANES) indicates the dominance of 3- over 4 -coordina te Cu in the primitive phase, while Cu L-3-edge spectra reveal only Cu (I) to be present in all precipitates formed. XPS data confirm the pre sence of only Cu(I) and reveal that three types elf S are present. Upo n ageing, the primitive structure transforms to one with the character istics of covellite, and this transformation involves the reordering o f the S-2- and Cu3S-CuS3-layers. Development of the primitive phase fr om either a wurtzite-like structure or planar Cu3S-CuS3-layers is poss ible, with the structural evolution driven by the antipathy of Cu(II) for tetrahedral coordination and anomalous electron densities in the m etastable structures. Copyright (C) 1997 Elsevier Science Ltd.