Structural, Optoelectronic, Magnetic, and Photoelectrochemical Consequences of Copper Insertion into Alkaline Earth Metal (Mg, Ca, or Sr) Pyrovanadate Compound Frameworks.

This study explores the manifold consequences of introducing copper into an alkaline earth metal (A = Mg, Ca, or Sr) pyrovanadate compound (A2V2O7) framework. Thus, powder X-ray diffraction coupled with Rietveld refinement showed that phase pure alloys, namely, Mg0.67Cu1.33V2O7, CaCuV2O7, and SrCuV2O7 could be obtained via solution combustion synthesis. Local structure distortions from copper insertion into the A2V2O7 compound framework were revealed by Raman spectroscopy and X-ray photoelectron spectroscopy. Importantly, the Cu2-xAxV2O7 alloy framework is shown below to be an excellent platform for demonstrating the complementarity of the two outcomes of bandgap photon absorption, namely, photovoltaic or photoelectrochemical (PEC) activity versus photoluminescence (PL). Thus, PL from the parent pyrovanadate was quenched when copper was introduced; concomitantly, PEC activity emerged for the semiconductor alloys. Changes in the electronic band structures on copper introduction were experimentally probed by diffuse reflectance spectroscopy and Kelvin probe measurements. These data were complemented by density functional theory (DFT) calculations. Finally, the magnetic attributes of the three alloys are discussed via both experiment and theory.