Electronic structure of Li-doped NiO

The electronic structure of ${\mathrm{Li}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$O has been investigated using x-ray photoemission spectroscopy (XPS), bremsstrahlung isochromat spectroscopy (BIS), and model-Hamiltonian cluster calculations. The measurements support the conclusion that the Li-doped holes have mainly oxygen character. The unoccupied electronic structure as probed with BIS shows broad structures growing in the gap. By comparing the XPS valence band to the results of the cluster calculations, we determine values for the Racah A parameter (=6.6 eV), charge transfer \ensuremath{\Delta} (=6.2 eV), and hybridization transfer integral (pd\ensuremath{\sigma}) (=1.3 eV). The first ionization state in the NiO valence-band cluster calculation is of $^{2}$${\mathit{E}}_{\mathit{g}}$ symmetry, a state in which the doped hole is antiferromagnetically coupled to the Ni spins. Hole-doped cluster calculations explain, because of a different fractional parentage upon annihilating a Ni 3d or an O 2p hole, the difference between the O 1s XAS results and the BIS results of heavily Li-doped NiO.