Polymorph-Induced Reducibility and Electron Trapping Energetics of Nb and W Dopants in TiO.

Controlling the formation of electron polarons in TiO doped with transition metals is important for the design of transparent conducting oxides for high-efficiency photovoltaics and photocatalysts with tunable reaction selectivities. In this work, EPR spectroscopy is combined with Hubbard-corrected density functional theory (DFT+), with refined atomic-like Hubbard projectors, to show the sensitivity of charge compensation in substitutionally doped Nb-TiO and W-TiO with respect to the TiO polymorph (, anatase or rutile). Both EPR magnetic tensors and DFT+predicted Nb 4 and W 5 orbital occupancies show the formation of differing dopant charge states depending on the TiO polymorph, with nonmagnetic Nb and W in doped anatase and paramagnetic Nb and W in doped rutile. The results provide an example of how a coherent experimental and theory-validated framework can be used to understand and predict the reducibility of dopants and electron trapping energetics in TiO polymorphs. The outcome enables greater control over the electronic and magnetic properties of metal oxide semiconductors, which are crucial for the rational design of next-generation materials for energy conversion and catalytic applications.