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, Mg_0.67Cu_1.33V₂O₇, 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 Cu_2–xA_xV₂O₇ 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.