Summary
Pt/TiO2-interfaces show Schottky-barrier or ohmic behavior depending on the diffusion of Pt into TiO2 subsurface layers. Diffusion effects are negligible for TiO2 rutile surface structures in the absence of oxygen at T≤1070 K. This leads to Schottky-barrier electrical behavior. If bulk diffusion of Pt is pronounced we observe ohmic behavior. This is the case for all TiO2 samples with nonstoichiometric Magneli-subsurface phases and for TiO2 rutile surface phases at T≥1070 K in the presence of oxygen. The latter is explained by reduced activation barriers of surface platinum during the first step of in-diffusion if platinum is present as an ion (Pt4+ or Pt2+) at the surface. Ions are formed as intermediates during the formation and decomposition of platinum oxide at the three-phase-boundary O2/Pt/TiO2.
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Kirner, U.K., Schierbaum, K.D. & Göpel, W. Interface-reactions of Pt/TiO2: Comparative electrical, XPS-, and AES-depth profile investigations. Fresenius J Anal Chem 341, 416–420 (1991). https://doi.org/10.1007/BF00321948
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DOI: https://doi.org/10.1007/BF00321948