Charge Transfer Across Oxide Interfaces Probed by in Situ X-ray Photoelectron and Absorption Spectroscopy Techniques

The interface between two functional oxide materials governs the physical, chemical, and electronic interactions between the two phases. We investigate the charge transfer across the interface between two structurally related material classes, namely, perovskite and Ruddlesden–Popper-type oxides, choosing La0.8Sr0.2CoO3−δ (LSC) and Nd2NiO4+δ (NNO) as our model systems for the two classes, respectively. The interface of Nd2NiO4+δ and La0.8Sr0.2CoO3−δ is investigated using in situ photoemission spectroscopy techniques on epitaxial thin films. A detailed analysis of the electronic structure with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy under an oxygen atmosphere and at elevated temperature reveals charge transfer from La0.8Sr0.2CoO3−δ into Nd2NiO4+δ. Through the use of electrical conductivity relaxation, it is demonstrated that such charge transfer from LSC into NNO is accompanied by a reduction in the kinetics of oxygen exchange on Nd2NiO4+δ, contrary to expectation. Fermi level pinning at the surface of Nd2NiO4+δ is discussed as a possible cause for this phenomenon. These insights add to the understanding of material interaction necessary for the design of next-generation high-performance electrochemical components