ELECTRONIC-STRUCTURE OF LA2-XSRXNIO4-X-RAY ABSORPTION AND EMISSION SPECTROSCOPIES(DELTA STUDIED BY SOFT)

The O-K x-ray absorption and emission measurements were performed on L a2-xSrxNiO4+delta with different delta and x. For doped compounds, a p repeak is observed near the O 1s edge associated with doping-induced u noccupied O 2p states. The O-K x-ray emission spectra of La2-xSrxNiO4delta exhibit changes in their profile with variation of the excitatio n energy through the O 1s edge which are due to the difference in the absorption cross section for inequivalent O sites and in the degree of the localization of unoccupied states. Analysis of the results obtain ed suggests that for the delta>0 sample the states in the O 1s prepeak are rather localized by trapping the induced holes in small anti-Jahn -Teller polaron while for the highly Sr-doped compounds these states h ave itinerant character and belong to mainly in-NiO2-plane oxygen.