Influence of Nitrogen Substitution on the Electronic Structure of Ti₂O₃: Insights into the Doping‐Induced Insulator‐to‐Metal Transition

Abstract

Although changes in the electronic structure of Ti2O3 across the insulator‐to‐metal transition (IMT) by thermal excitation are generally investigated, the role of chemical doping in this context deserves attention. To gain insights into that, soft X‐ray photoelectron (XPS) and absorption spectroscopy (XAS) are adopted to investigate the electronic structure of Ti2O3 upon N doping. Core‐level and valence‐band spectra shift consistently to lower binding energies with N doping, indicating a downward movement of the Fermi level (EF) toward the surface. Meanwhile, valence‐band data reveals an increase in the electron population of the conduction band upon doping. The XAS results at the Ti L‐ and O K‐edge indicate that the a1g orbitals are partially occupied in the Ti3+ sites by N doping, with an enhanced Ti 3d–O 2p hybridization. Consistently, the density functional theory (DFT) calculations illustrate the metallic behavior in an N‐substituted system. It is important that N substitution results in a mixing of the a1g and egπ states because of considerable broadening of a1g orbitals across EF. These observations demonstrate the importance of Ti 3d‐a1g occupation relevant for transportation. This may provide significant insights into the IMT behavior after N doping in Ti2O3.