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

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 (E-F) 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 a(1g) 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 a(1g) and e(g)(pi) states because of considerable broadening of a(1g) orbitals across E-F. These observations demonstrate the importance of Ti 3d-a(1g) occupation relevant for transportation. This may provide significant insights into the IMT behavior after N doping in Ti2O3.