Phase Stability Diagrams of Group 6 Magnéli Oxides and Their Implications for Photon-Assisted Applications

Controlling the stoichiometry and metastability in functional oxides is often the key to enhance their performance for a range of important oxide-based technological applications. In this work, using the recently developed meta-generalized-gradient approximation (GGA) and hybrid density functional theory calculations, we study both stoichiometric and substoichiometric (Magnéli) oxides of tungsten and molybdenum, focusing on their structural parameters, growth thermodynamics, and electronic structure for targeted photo-related applications. We report that the substoichiometric Magnéli phases of tungsten oxides (namely, W₅O₁₄ and W₁₈O₄₉) are found to be stable under both gas- and solution-based synthesis environment, whereas the substoichiometric Magnéli phases of molybdenum oxides (namely, Mo₉O₂₆, Mo₅O₁₄, and Mo₄O₁₁) prefer to form only under gas-phase synthesis. We highlight how these n-doped substoichiometric Magnéli heavy metal oxides are indeed the choice candidate materials for solar water splitting (within the Z-scheme) and act as interfacial hole transport layers for the next-generation photodevices.