Substitution-induced midgap states in the mixed oxides RxBa1-xTiO3- delta with R=Y, La, and Nd.

Changes induced in the electronic structure of BaTiO 3 by substitutions of R=Y, La, or Nd for Ba to form the mixed oxides R x Ba 1-x TiO 3-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. Various contributions to the binding energy and width of these states are considered

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