TUNABLE EXCITATION X-RAY-FLUORESCENCE SPECTROSCOPY IN PHASE-ANALYSIS OF HIGH-TC SUPERCONDUCTORS

O Kalpha x-ray fluorescence of YBa2Cu3O7-delta and Sr0.85Nd0.15CuO2 sa mples containing CO3(2-) impurities, as well as pure BaCO3, have been studied using tunable monochromatic synchrotron radiation excitation. When the excitation energy is set to the most intense features in the O 1s absorption edge of cuprates and to bound states above this edge t he O Kalpha spectra recorded are very similar to those of pure BaCO3 e ven if the admixture of CO3(2-) is small. The observed changes in the O Kalpha profiles of multi-phase YBa2Cu3O7-delta and Sr0.85Nd0.15CuO2 samples are discussed in terms of different x-ray absorption cross sec tions for O in the main phase and in the CO3(2-) fraction.