A Greener Solid-State Route to Thermochromic VO₂(M1) Powders: Low-Vacuum Synthesis with Minimal Waste and Tungsten Doping

A simplified solid-state route for the synthesis of thermochromic vanadium dioxide (VO₂(M1)) and tungsten-doped VO₂ is reported, based on mechanical compaction and thermal treatment under moderate vacuum, without the use of inert gas atmospheres, solvents, or reducing agents. The process relies on commercially available solid precursors and operates at 750 °C, yielding phase pure VO₂(M1) powders with sharp and reversible monoclinic–rutile transitions, as confirmed by differential scanning calorimetry and X-ray diffraction. Replacing continuous argon flow with mechanical pressure and moderate vacuum, the synthesis reduces auxiliary material inputs, eliminates dependence on high-purity inert gas supply chains and simplifies reactor operation while maintaining crystallinity and thermochromic behavior confirmed by thermal analysis. Tungsten doping using ammonium metatungstate was further demonstrated; while single cycle processing resulted in heterogeneous incorporation, iterative pressing and grinding cycles significantly improved compositional uniformity, leading to dominant low-temperature phase transition and subtle diffraction peak shifts consistent with W substitution. Overall, this solvent-free, low-vacuum solid-state approach establishes a scalable and resource-efficient framework for producing functional oxides with tunable thermochromic properties through simplified atmosphere control at laboratory scale.