Reductive mechanochemical synthesis of alkali molybdenum bronze nanoparticles

The synthesis of two mixed-valent oxides of Mo using mechanochemical methods was presented. The reactions proceed via two-steps including ball milling and an annealing step. Two alkali molybdenum oxides bronzes of special interest, K_0·3MoO₃ and Na_0.9Mo₆O₁₇ were considered. The structures and stoichiometry are supported by powder X-ray diffraction and energy dispersive X-ray spectroscopy measurements. It was found that the effects of ball milling significantly reduce the time required (from 12 or more to 4 h) to complete the reaction by creating solid solutions which dramatically lower the melting point of MoO₃ from around 800 °C–400 °C. Additionally, we demonstrate the use of ball milling to synthesize nanoparticles of these bronzes with controlled size distributions, with average length down to 7.7 ± 2.5 nm; shown by pXRD and transmission electron microscopy measurements. The results demonstrate the possibilities for reducing total reaction times necessary for the formation of complex oxides by combining mechanochemical methods with additional synthetic routes. This methodology, as well as the ability to control product size, enables further investigation of size-dependent electronic phenomena in these systems.