Substitution-induced mid-gap states in R x Ba1−xTiO3−δ whereR = Y, La, and Nd
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Changes induced in the electronic structure of BaTiO3 by substitutions of R = Y, La or Nd for Ba to form the mixed oxides R x Ba1−xTiO3−δ have been investigated using ultraviolet photoelectron spectroscopy. Substitution of formally R+3 ions for Ba+2 leads to the introduction of filled states in the band gap that are shown by resonant photoemission measurements to have significant Ti 3d character, consistent with a Mott-Hubbard insulator description for these oxides. It is suggested that the dominant factor is electron-electron correlation and this leads to the estimatesU∼Δ∼3 eV for this system, whereU is the correlation energy for the 3d and Δ is the charge transfer energy. Changes are observed in the photoelectron spectral shape for these states as a function of increasing substitution in the Nd system and discussed in the context of the opening of the Hubbard gap.
Key wordsMixed oxides doping electronic structure photoemission
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