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Co2+/3+ and Fe2+/3+ charge transition levels in (La,Sr)CoO3−δ and (La,Sr)FeO3−δ

Yue Liu, Stefanie Frick, Katharina N. S. Lohaus, and Andreas Klein*

  • *Contact author: aklein@esm.tu-darmstadt.de
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Phys. Rev. Materials 9, 075405 – Published 25 July, 2025

DOI: https://doi.org/10.1103/tn7z-thjk

Abstract

X-ray photoelectron spectroscopy (XPS) is used to determine the energy levels associated with the Co2+/3+ and Fe2+/3+ charge transition levels in (La,Sr)CoO3−δ and (La,Sr)FeO3−δ, respectively. The charge transition levels are revealed by varying the Fermi level by means of oxidizing and reducing treatments. The Co2+/3+ transition occurs at 0.15±0.05eV above the valence band maximum of (La,Sr)CoO3−δ and the Fe2+/3+ transition at 1.25±0.05eV above the valence band maximum of (La,Sr)FeO3−δ, respectively. In combination with the energy band alignment determined from XPS analysis in the course of interface formation, it is derived that the energetic difference of the charge transition levels coincides with that in Co-doped BiFeO3, suggesting transferability of the energy levels in perovskite-type materials. The difference in charge transition levels directly relates to the easier reduction of Co compared to Fe. The result emphasizes that the oxidation states of Fe and Co in mixed compounds must be treated independently for a quantitative description of (defect) properties. They also provide a natural direct explanation for the higher electronic conductivity of (La,Sr)CoO3−δ compared to that of (La,Sr)FeO3−δ, and for the acceptor behavior of Co in (La,Sr)FeO3−δ.

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Phys. Rev. Materials 9, 075405– Published 25 July, 2025
  • Received 22 January 2025
  • Revised 25 April 2025
  • Accepted 15 July 2025
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