The change in the electronic structure across the metal/insulator transition in a Mott-Hubbard system was investigated by means of X-ray absorption and photo-emission spectroscopy. The results were compared with those for CeTiO3, where hole doping was achieved by excess O instead of Sr substitution. It was found that additional doped-hole states were created in the insulator gap for both cases, while the density of states at the Fermi level in CeTiO3, was almost half of that in (Ce,Sr)TiO3, for the same nominal doping. It was suggested that there was a large reduction in the mobility of carriers due to cation vacancies which were produced by excess O.

Electronic Structure of Ce1-xSrxTiO3: Comparison between Substitutional and Vacancy Doping. T.Yokoya, T.Sato, H.Fujisawa, T.Takahashi, A.Chainani, M.Onoda: Physical Review B, 1999, 59[3], 1815-8