Surface Electron-Ion Mixed Conduction of BaTiO3-delta Thin Film with Oxygen Vacancies

A BaTiO3-delta thin film with oxygen vacancies was prepared on a Pt/Al2O3 (0001) substrate by RF magnetron sputtering. The prepared thin film was preferentially grown in the [111] direction. The BaTiO3-delta thin film with a reduced interplanar distance (d(111)) exhibited the Ti3+ valence state of 4.4%, which is closely related to concentration of oxygen vacancies. The activation energy estimated from the Arrhenius plot of the electrical conductivity was approximately 61 meV. The electrical conductivity of similar to 10(-5) S/cm at room temperature did not depend on the oxygen gas partial pressure. The photoemission spectra exhibited the O-H bond peak and donor state near the Fermi level. These results indicate that the BaTiO3-delta/Pt/Al2O3 (0001) thin film has surface electron -proton mixed conduction at room temperature.