Exploring oxygen vacancies and electronic structure in delafossite CuCoO₂ Using XAS and XANES Measurements

Abstract We report on the electronic properties of Cu based Delafossite material (CuCoO 2 ) for the first time, using metal and oxygen K-edge and metal L 3,2 -edge x-ray absorption spectroscopy (XAS). The structural and morphological characterization are carried out using x-ray diffraction, Fourier transfer infrared spectroscopy (FTIR) and electron microscopy. To study the benign effect reported for the bi-metallic TMO, which reinforces the electrochemical energy storage capacity of bi-metallic-TMO compared to the monometallic counterpart, we have studied the electronic properties using K-edge x-ray absorption near edge spectroscopy (XANES) at Cu, Co and O edges. In addition, L 3,2 edge x-ray absorption spectra (XAS) for Cu and Co are reported. From Cu and Co edge XANES, we find that these are in +1 and +2.93 oxidation states, respectively. Oxygen deficient CoO 6 octahedra present defects and possible sites for charge storage. Oxygen vacancies are the main defects, which prefer Co sites compared to Cu sites. Co ions show higher Ligand Field splitting than reported for other transition metal oxides. Co ions in CuCoO 2 delafossite were found to be in low spin state, in agreement with literature. Cu +1 (electronic configuration: [Ar] 3d 10 ) L 3,2 edge XAS shows absorption peaks due to (2p 6 )(3d 9 L)–(2p 5 L )(3d 10 ) and (2p 5 L )(3d 9 L)–(2p 4 L 2 )(3d 10 ) transitions, where L and L are the holes in d and p orbitals, respectively.