The Fermi energy in acceptor doped SrTiO3 and BaTiO3
March 10-14, 2019
In order to evaluate the presence of space charge layers and the magnitude of band bending at electrode interfaces of mixed ionic-electronic conductors we have evaluated the Fermi energies in the bulk and at interfaces of acceptor-doped SrTiO3, BaTiO3 and (Ba,Sr)TiO3. While the interface Fermi energy can be directly obtained using photoelectron spectroscopy (XPS) if conducting electrode materials are deposited, the determination of the bulk Fermi energy is more challenging due to the high resistivity of the samples. One approach is to use XPS on thin films deposited on conducting samples. In general, we observed a good agreement between upper and lower limits of Fermi energies at thin films surfaces and at interfaces. Surprisingly, the Fermi energy is hardly observed below EF-EVB≈2eV (see Fig. 1), although defect chemistry calculations predict values as low as EF-EVB≈2eV for acceptor doped samples, such as Fe-doped SrTiO3 or Mn-doped BaTiO3.c,d Even at anode interfaces of ionically polarized Fe-doped SrTiO3 single crystals,e at which the oxygen vacancy concentration should be very low, we have not observed lower Fermi energies.
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Andreas Klein, Leonard Gura, Binxiang Huang, Katharina Schuldt, Issei Suzuki, Christopher Castro Chavarria, and Mario Maglione, "The Fermi energy in acceptor doped SrTiO3 and BaTiO3" in "Nonstoichiometric Compounds VII", ECI Symposium Series, (2019). https://dc.engconfintl.org/nonstoichiometric_vii/21