THE ELECTRONIC-STRUCTURE OF TI4O7 STUDIED BY RESONANT PHOTOEMISSION

We present and discuss resonant photoemission (PES) spectra of Ti4O7 t aken at 50 and 300 K. The PES spectra taken in the metallic phase at 3 00 K show Ti 3d bands at the Fermi level and O 2p bands at higher bind ing energies. The intensity of the Ti 3d bands increases for photon en ergies above 40 eV. This effect is attributed to a constructive interf erence with the Ti 3p --> 3d resonance which is confirmed by the corre sponding constant-initial-state (CIS) spectra. The Ti 3d bands shift a pproximately 0.25 eV towards higher binding energies in the low temper ature semiconducting phase at 50 K. This shift reflects the opening of the band gap and provides a rough estimate of the electronic contribu tion to the formation energy of the Ti3+-Ti3+ pairs in the low-tempera ture phase.