Journal
APPLIED SURFACE SCIENCE
Volume 256, Issue 21, Pages 6228-6232Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.apsusc.2010.03.146
Keywords
BaTiO3 and titanates; Films; PTCR; Segregation; Surfaces; XPS
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Funding
- Conseil Regional diAquitaine in France
- Deutsche Forschungsgemeinschaft [Sonderforschungsbereich 595]
- European Multifunctional Materials Institute (EMMI), through collaboration between the Institute of Condensed Matter Chemistry of Bordeaux (ICMCB) and the Institute of Materials Science of Darmstadt
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We have used in situ photoemission spectroscopy to investigate Niobium doping in polycristalline BaTiO3. The valence band maximum position progressively shifts from 2.5 eV for undoped to 2.84 eV for Nb-doped films. Ceramics and single crystal have been investigated for comparison with thin films. Nb-doped BaTiO3 ceramics and Nb-doped SrTiO3 single crystal show higher Fermi level position indicating that our doped films are less conducting regarding their bulk parents. This was confirmed by impedance spectroscopy under variable temperature. Large amount of niobium is clearly observable at surface but the amount of dopant is drastically reduced below the near-surface region, as evidenced by depth profile. Therefore, we provide evidence of surface segregation which would explain the contrasted resistivity values reported in literature for such donor-doped films. (C) 2010 Elsevier B.V. All rights reserved.
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