Microwave-Assisted Solvothermal Synthesis of Spinel AV₂O₄ (M = Mg, Mn, Fe, and Co)

Abstract

Lower-valent vanadium oxide spinels AV₂O₄ (A = Mg, Mn, Fe, and Co) consisting of A²⁺ and V³⁺ ions have been synthesized by a low-temperature microwave-assisted solvothermal (MW-ST) synthesis process in a tetraethylene glycol (TEG) medium. The oxides are formed within a short reaction time of 30 min at 300 °C. Subsequent postheat treatment of the oxides at elevated temperatures in inert or reducing atmospheres results in an instability of the spinel phase, especially CoV₂O₄ due to the ease of formation of metallic Co, demonstrating the advantage of the low-temperature MW-ST process in accessing these oxides. This MW-ST synthesis approach is attractive for synthesizing other lower-valent transition-metal oxides that are otherwise difficult to obtain by conventional synthesis methods and for subsequent study of their unique physical and chemical properties