Electronic structure of Ce1-xSrxTiO3: Comparison between substitutional and vacancy doping

The change of the electronic structure across the metal-insulator transitio n in a Mott-Hubbard system Ce1-xSrxTiO3 has been investigated by x-ray abso rption and photoemission spectroscopy. The results are compared with CeTiO3 +delta, where hole doping is achieved by excess oxygen instead of Sr substi tution. It is found that additional doped-hole states are created in the in sulator gap for both cases, while the density of states at the Fermi level in CeTiO3+delta, is nearly half of that in Ce1-xSrxTiO3 at the same nominal doping. This suggests a strong reduction in the mobility of carriers due t o cation vacancies produced by excess oxygen. [S0163-1829(99)03803-5].