Polymorph-Induced Reducibility and Electron Trapping Energetics of Nb and W Dopants in TiO₂

Abstract

Controlling the formation of electron polarons in TiO₂ doped with transition metals is important for the design of transparent conducting oxides for high-efficiency photovoltaics and photocatalysts with tuneable reaction selectivities. In this work, EPR spectroscopy is combined with Hubbard-corrected density functional theory (DFT+U), using refined atomic-like Hubbard projectors, to show the sensitivity of charge compensation in substitutionally doped Nb–TiO₂ and W–TiO₂ with respect to the TiO₂ polymorph (i.e., anatase or rutile). Both EPR magnetic tensors and DFT+U predicted Nb 4d and W 5d orbital occupancies show the formation of differing dopant charge states depending on the TiO₂ polymorph, with non-magnetic Nb⁵⁺ and W⁶⁺ in doped anatase, and paramagnetic Nb⁴⁺ and W⁵⁺ in doped rutile. The results demonstrate how a coherent experiment-and-theory-validated framework can be used to understand and predict the reducibility of dopants and electron-trapping energetics in TiO₂ polymorphs. The outcome enables greater control over the electronic and magnetic properties of metal-oxide semiconductors, which is crucial for the rational design of next-generation materials for energy-conversion and catalytic applications.

Citation: A. Chaudhari, A. J. Logsdail and A. Folli, Polymorph-Induced Reducibility and Electron Trapping Energetics of Nb and W Dopants in TiO₂, The Journal of Physical Chemistry C, 2025, 129 (34), 15453-15461, DOI: 10.1021/acs.jpcc.5c04364