The electronic structure of CoO, Li doped CoO and LiCoO¬2

The electronic structure of Li x Co 1-x O (0.01≤x≤0.2), LiCoO 2 , and Co 3 O 4 (1% Li) has been investigated using x-ray photoemission spectroscopy (XPS), bremsstrahlung isochromat spectroscopy (BIS), and x-ray-absorption spectroscopy. The experimental results are compared with model cluster calculations. We find that the CoO band gap is of an intermediate character, between Mott-Hubbard-like and charge-transfer-like. The first ionization state of CoO is therefore of strongly mixed Co 3d and O 2p character. Its local symmetry corresponds to 3 T 1g , similar to an intermediate-spin Co 3+ state. For x≤0.2 the local Co electronic structure is similar to that of CoO. However, LiCoO 2 has a strongly reduced Co-O interatomic distance, resulting in a ligand field strong enough to stabilize a Co 3+ low-spin ground state. LiCoO 2 is an insulator with a gap of 2.7 eV. From a comparison of the XPS and BIS CoO spectra to the cluster calculations, we find values for U (=5.3 eV), Δ (=5.5 eV), and (pdσ) (=1.3 eV).