Cu 2p absorption spectroscopy as a probe for the site occupancy of (Zn_xCu_1-x)WO₄ solid solution

The solid solution sanmartinite (ZnWO₄)-cuproscheelite (CuWO₄) has been studied using Cu 2p X-ray absorption spectroscopy. While a single L₃ absorption peak is observed for CuWO₄, two distinct L₃ absorption peaks with a separation of ∼0.8 eV are observed for the intermediate samples in the solid solution. The two peaks represent distinct Cu sites: one with all CuO₆ next nearest neighbours in the (Cu,Zn)O₆ chains, another having at least one ZnO₆ next nearest neighbour. Both sites show a linear increase in covalency as a function of increasing Cu-content. The relative intensities of the two absorption peaks is dependent upon the Cu-content and has been used to model the site occupancies. The results reveal that the local structural effects can be associated with a composition-dependent structural phase transition from P2/c (ZnWO₄) to P {Mathematical expression} (CuWO₄). Deviations from a single-site model are explained in terms of the local environments, and evidence for site preferences and local clustering are explored.