Cu 2p absorption spectroscopy as a probe for the site occupancy of (ZnxCu1−x)WO4 solid solution

Abstract

Abstract. 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 L 3 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)O 6 chains, another having at least one ZnO 6 next nearest neighbout. 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 (ZnWO~) to P1 (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.

Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals

“…Therefore, when subjected to extreme pressure environments, the researchers [40][41][42][43] have reported that these crystals have a monoclinic structure characterized by space group (P2/c), point group symmetry (C 4 2h ) and two molecular formula units per unit cell (Z = 2) [43,44]. On the other hand, under low-pressure conditions at room temperature, these crystals exhibit a triclinic structure with space group (P 1), point group symmetry (C i ) and two molecular formula units per unit cell (Z = 2) [45][46][47]. Moreover, CuWO 4 crystals with triclinic structure are influenced by Jahn-Teller effect due to the presence of Cu 2+ ions, which promote distortions on octahedral [CuO 6 ] clusters.…”

Cu and Zn ordering in aurichalcite

“…Thus, as may be expected from crystal chemistry, it follows that in all the samples Cu 2+ is located in more than one site. Such additional features have been used previously to model site occupancies ifi (ZnxCUl_x)WO 4 (Schofield et al, 1993), but are not sufficiently detectable for such analysis here. If these features are indeed due to multiple site occupancies, then the different energy and shape of the L3 peaks for BM 1964,702 andBM 1983,97 from that of BM 1937,1355 may be assigned to an extra absorption component representing the existence of an extra Cu 2+ site.…”

Chemical-state analyses of Ni, Zn, and W ions in NiWO$_4$-ZnWO$_4$ solid solutions by X-ray photoelectron spectroscopy

“…Tungstates have technologically important applications as scintillators [1], laser host materials [2], photocatalysts [3], and heterogeneous catalysts [4]. Many properties of tungstates can be further controlled by doping or by making solid solutions with other tungstates [5,6,7,8,9,10]. The doping approach is of particular interest because of a wide range of possible chemical compositions.…”

“…Both ZnWO 4 and NiWO 4 crystallize in the wolframite structure (space group P 2/c) with two formula units per unit cell [11,12] ] octahedra. However, multiple articles showed that on a microscopic level the local structure in these (or similar) materials can be quite complex [5,10]. The formation of solid solutions also changes the environment around B cations and increases the unit cell volume in proportion to A concentration (for Zn c Ni 1 -c WO 4 , see [13,14,15]; the ionic radii are 0.72 Å and 0.69 Å for Zn and Ni, respectively [16]).…”