The electronic structure of Ti4O7 studied by resonant photoemission.

We present and discuss resonant photoemission (PES) spectra of Ti4O7 taken at 50 and 300 K. The PES spectra taken in the metallic phase at 300 K show Ti 3d bands at the Fermi level and O 2p bands at higher binding energies. The intensity of the Ti 3d bands increases for photon energies above 40 eV. This effect is attributed to a constructive interference with the Ti 3p → 3d resonance which is confirmed by the corresponding constant-initial-state (CIS) spectra. The Ti 3d bands shift approximately 0.25 eV towards higher binding energies in the low temperature semiconducting phase at 50 K. This shift reflects the opening of the band gap and provides a rough estimate of the electronic contribution to the formation energy of the Ti3+-Ti3+ pairs in the low-temperature phase.