p–d coupling: prerequisite for band-like doping levels in metal oxides

Abstract

Identifying the prerequisite of inducing band-like doping levels in wide bandgap metal oxides is a crucial yet open question. Herein, taking boron (B) and nitrogen (N) codoped anatase TiO₂ as an example and combining density functional theory calculation with machine learning, it has been revealed that the band-like doping levels mainly originate from a strong p–d coupling between O/N-p_π and Ti-t_2g orbitals. Significantly, the existence of strong p–d coupling is an intrinsic characteristic of anatase TiO₂ determined entirely by crystal symmetry, which can be used as a universal criterion to predict whether band-like doping levels can be induced in other metal oxides, and the criterion has been fully verified on rutile and brookite TiO₂, ScTaO₄, WO₃, SnO₂ and MgTa₂O₆. Besides, the strong p–d coupling offers a theoretical basis for the long-held empirical understanding that uniform doping is important in achieving stronger visible light absorption for wide bandgap metal oxide photocatalysts. Overall, the uncovered strong p–d coupling provides a simple yet profound guideline for bandgap engineering of metal oxides.