Cuprous delafossites, Cu3(MFeSb)O6 (M = Na, Li) with honeycomb arrays, realized by topochemical ion-exchange reactions

The current work describes the synthesis, structure, magnetic and optical properties of Cu1+ based delafossite oxides, Cu-3(MFeSb)O-6 (M = Na, Li) synthesized by the topotactic ion-exchange reactions (around 400 degrees C) of CuCl with Na4FeSbO6 and Na3LiFeSbO6 in an inert argon atmosphere. The synthetic procedure is significant as the oxides could not be synthesized by the solid state methods. Chemical analysis coupled with energy dispersive spectral analysis confirmed the extent of replacement of Na+ ions by Cu+ ions. A complete exchange of alkali metal ion, Na+ by Cu1+ in the interlayers of these honeycomb oxides has been achieved using a ratio of 1:3 between Na4FeSbO6 and CuCl. An additional exchange of approximately 70 % Na+ ions from the honeycomb arrays is possible by varying the ratio to 1:4. Rietveld refinements (space group C2/c) of the powder X-ray diffraction data have been carried out to ascertain the phase purity and to verify the structure formed by edge shared honeycomb arrays separated by Cu1+ in dumbbell configuration (O-Cu1+-O). X-ray photoelectron spectroscopy analysis confirmed the oxidation states of the constituent ions, specifically copper as Cu1+. A similar method is adopted to synthesize Cu-3(LiFeSb)O-6 by reacting Na-3(LiFeSb)O-6 and CuCl in the ratio 1:3 at 400 degrees C. These new delafossite oxides, Cu-3(MFeSb)O-6 (M = Na, Li) and Cu-3((Cu0.7Na0.3)FeSb)O-6, exhibit interesting magnetic properties which are significantly different from the rock salt based parent sodium analogs. Dominant antiferromagnetic interactions with a specific ordering temperature have been observed for these samples containing Fe3+ (d(5)) ions in the honeycomb. UV-visible diffuse reflectance measurements indicated the decrease in the band gap of Cu1+ based oxides. This study highlights the importance of low temperature ion-exchange reactions as an effective route to stabilize multifunctional materials of potential importance for various applications.

Automated summary

This study describes the synthesis, structure, magnetic and optical properties of Cu1+ based delafossite oxides. The results demonstrate the unique properties of these oxides in honeycomb structures, which have potential importance for various applications.