CU 2P ABSORPTION-SPECTROSCOPY AS A PROBE FOR THE SITE OCCUPANCY OF (ZNXCU1-X)WO4 SOLID-SOLUTION

The solid solution sanmartinite (ZnWO4) - cuproscheelite (CuWO4) has b een studied using Cu 2p X-ray absorption spectroscopy. While a single L3 absorption peak is observed for CuWO4, two distinct L3 absorption p eaks with a separation of approximately 0.8 eV are observed for the in termediate samples in the solid solution. The two peaks represent dist inct Cu sites: one with all CuO6 next nearest neighbours in the (Cu,Zn )06 chains, another having at least one ZnO6 next nearest neighbour. B oth sites show a linear increase in covalency as a function of increas ing Cu-content. The relative intensities of the two absorption peaks i s dependent upon the Cu-content and has been used to model the site oc cupancies. The results reveal that the local structural effects can be associated with a composition-dependent structural phase transition f rom P2/c (ZnWO4) to P1BAR (CuWO4). Deviations from a single-site model are explained in terms of the local environments, and evidence for si te preferences and local clustering are explored.