XAS and XPS study of electronic structure of the trivalent cuprate La2Li0.5Cu0.5O4− δ

Abstract

Well-characterized stoichiometric La 2 Li 0.5 Cu 0.5 O 4− δ ( δ ≈0.04) has been studied using high resolution CuL 3- and OK-edges absorption (XAS) and Cu 2p 3 2 X-ray photoelectron spectroscopy (XPS) techniques. The system is found not to have any Cu 3 d 8 configuration in its ground state but instead reveals a high density of the holes created by doping of monovalent lithium for the divalent copper in the oxygen 2 p levels resulting in a 3 d 9 L copper configuration by charge transfer. The formal valence of copper in it is found to be as high as ≈2.84 in agreement with chemical analysis. The empirical correlation between the shift of the main XPS line (3 d 10 L) and intensity ratio of the satellite (3 d 9) to the main line is examined and, also, a new correlation between the energy spread of the XPS satellite and the energy separation of the CuL 3 absorption lines due to transitions from (3 d 9) and (3d d 9 L) states is suggested.