ELECTRONIC-STRUCTURE OF BI2SR2CACU2O8+DELTA AND TL2BA2CACU2O8 - NEAR-O-1S-THRESHOLD EXCITATION X-RAY FLUORESENCE STUDIES

The character of unoccupied and occupied states in Bi2Sr2CaCu2O8+δ and Tl2Ba2CaCu2O8 was investigated by measuring O 1s x-ray absorption and O Kα x-ray emission spectra. To record the latter, various excitation energies around the O 1s edge were used. An appreciable excitation energy dependence for the emission spectra was observed and it was attributed to changes in the relative number of excited inequivalent oxygen atoms. It was found that the first, second, and third prepeaks near the O 1s edge of the Tl-based cuprate are mainly related to the oxygen atoms in the CuO2, BaO, and TlO planes, respectively, whereas, the single prepeak in the O 1s absorption spectrum of Bi2Sr2CaCu2O8+δ is due to transitions to the in-CuO2-plane oxygen 2p states. Analysis of the results obtained suggests that there are doping-induced holes on all the types of the O atoms in Tl2Ba2CaCu2O8 and only at in-CuO2-plane oxygen sites in Bi2Sr2CaCu2O8+δ. © 1995 The American Physical Society.