The interstitial oxygen formation mechanism in La2NiO4-based oxides was studied using soft X-ray absorption spectroscopy. When the interstitial oxygen concentration increased, the pre-edge peak of O K-edge spectra increased while Ni L-edge spectra was almost invariant. These spectral changes strongly suggest the significant contribution of ligand oxygen to interstitial oxygen formation by providing/accepting electronic charge carriers. The variation of the integrated peak intensity of the O K-edge strongly suggests that interstitial oxygen formation is determined by the equilibrium unoccupied pDOS of ligand oxygen. From this hypothesis, we propose that modulating the electronic structure is the key to control the capability of interstitial oxygen formation in La2NiO4-based oxides.

An operando soft X-ray absorption spectroscopic technique, which enabled the analysis of the electronic structures of the electrode materials at elevated temperature in a controlled atmosphere and electrochemical polarization, was established and its availability was demonstrated by investigating the electronic structural changes of an La NiO dense-film electrode during an electrochemical oxygen reduction reaction. Clear O K-edge and Ni L-edge X-ray absorption spectra could be obtained below 773 K under an atmospheric pressure of 100 ppm O /He, 0.1 % O /He, and 1 % O /He gas mixtures. Considerable spectral changes were observed in the O K-edge X-ray absorption spectra upon changing the PO2 and application of electrical potential, whereas only small spectral changes were observed in Ni L-edge X-ray absorption spectra. A pre-edge peak of the O K-edge X-ray absorption spectra, which reflects the unoccupied partial density of states of Ni 3d-O 2p hybridization, increased or decreased with cathodic or anodic polarization, respectively. The electronic structural changes of the outermost orbital of the electrode material due to electrochemical polarization were successfully confirmed by the operando X-ray absorption spectroscopic technique developed in this study.

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In this study, in situ soft X-ray absorption spectroscopy (soft XAS) technique, which enables us to analyzeelectronic structures of oxides at elevated temperatures while controlling atmospheric conditions, was developed. The technique was applied to investigate the electronic structures of La 0.6 Sr 0.4 CoO 3-δ. X-ray absorption spectra at the Co Ledges and the O

In-situ simultaneous measurement technique of soft X-ray absorption and X-ray emission spectroscopy, which was available for atmospheric pressure and high temperature, was developed. This technique is expected to provide direct information about electronic structures, both occupied and unoccupied pDOS, of functional materials under controlled atmospheric and temperature conditions. In this work, this technique was applied to simultaneously measure O K-edge X-ray absorption and X-ray emission spectra of LaCoO 3 -based oxides under various oxygen partial pressure and temperatures. Clear O K-edge spectra could be obtained even in 1 bar of 100 ppm O 2 -He, 0.1%O 2 -He and 1%O 2 -He atmospheres below 873 K. The changes of the O K-edge X-ray absorption and X-ray emission spectra due to the changes of oxygen partial pressure and temperature were discussed in terms of changes of defect concentrations and spin states of the oxides. Availability of the developed in-situ simultaneous spectroscopic technique was successfully demonstrated.