Amorphous intermediates and discovery of a kinetic polymorph of BiVO₄ from heating V+Bi+Zn single-source precursors

Molecular single-source precursors are a promising way of obtaining multi-element extended solids directly. We show that thermal decomposition of well-defined mono-, bi- and trimetallic polyoxovanadates (POVs) proceeds through a series of intermediate amorphous and crystalline species which we characterise using solid-state NMR spectroscopy, pair-distribution function (PDF) analysis and in-situ X-ray diffraction, before forming crystalline V₂O₅ and BiVO₄ products. This synthetic strategy enables the formation of phases inaccessible using other routes, including a previously unknown polymorph of BiVO₄ which we name β-BiVO₄ due to its similarity to β-SnWO₄. Local structure information also reveals the temperature dependent incorporation of Zn do pants into BiVO₄. The study also explores the electrochemical properties of amorphous mixed-valence vanadium oxides as Li-ion battery electrodes. We suggest that careful analysis of the thermal decomposition of molecular species may be a way of obtaining hitherto unknown kinetically stabilised polymorphs and amorphous variants of extended solids.