Quemchnlttsveranderung elner Ag-Au-Diffuslonsprobe nach 98h be1 Woo C. Vergr. 72 x Bild 4 Ag-Au-Probe nach 98 h be1 9000 C elektrolytlsch gentzt mlt 1 % KCN-Losung. Vergr. 75 x Au
Abstract. The High Temperature Superconductors are characterized by a very anisotropical structure and by typical arrangements of Cu-and O-atoms within CuO2-planes. In studying the electronic structure of these compounds there is a strong demand for high resolution valence band spectroscopy. Using an electron probe microanalyzer we study the X-ray emission of O-K~ and Cu-L, emerging from polycrystalline YBa2 Cu30 7 and T12 Ba2 Ca2 Cu3010. The O-K~ emission band is analyzed using a chlinochlore crystal in (001) orientation (2d = 28.4 A). For the Cu-L~ emission band we use a beryl crystal in (1010)-orientation (2d = 15.9 A). Furthermore, orientation dependent X-ray emission spectroscopy of single-crystalline YBa 2 Cu a O7 and T12 Ba 2 Ca1 Cu2 08 specimens was performed. We present the partial O-K~ spectra which represent the O-2p, (r/= x, y, z) electronic densities of states of the valence band and compare them with calculated data.Key words: high-To superconductors, electron probe microanalyzer, polarized X-ray emission, partial density of states, spectrometer crystals.For the copper-oxide superconductors with a high transition temperature T c it is generally accepted, that the assumption of a pure electron-phonon mechanism is inadequate for the description of the high To-values.Along with other theoretical models concerning the unknown origin of high Tr superconductivity, it was suggested that charge transfer excitations from occupied bonding to unoccupied anti-bonding states induce an attractive interaction between the conduction electrons in the CuO 2 planes. This excitonic mechanism, leading to the formation of Cooper-pairs, is one of the competing models.For the elucidation of the correct mechanism or mechanisms involved, experimental studies of these high To-superconductors will at least eliminate some of the competing models or indicate the validity of corresponding theories.
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