THE ELECTRON AND LATTICE PROPERTIES OF SUPERCONDUCTING CERAMICS YBCO-CL

A complex investigation of thermodynamic and structural characteristics, NMR-spectra, Cu K XANES- and X-ray Cu Lalpha fluorescent spectra was carried out on the yttrium ceramics YBa2.01Cu2.92O6.54Cl0.61. The NMR-spectra of these HTSC have shown that the chlorine ions occupy three definite positions in the lattice of the starting yttrium ceramics. Comparison of these data with the neutron diffraction analysis results allowed us to estimate quantitative relations of the distribution of halogen ions among the three positions O(5), O(4) and O(1). It has been shown by XANES-spectroscopy that no considerable amount (more than 10% of sample volume) of the halogen-free phase is observed in the chlorinated ceramics. In this connection some models, widespread in the literature, in which the halogen ions diffusing in the ceramics displace the oxygen and form the oxygen superconducting phase YBa2Cu3O7 inside the crystallite, seem to be erroneous. Analysis of the temperature dependence of the heat capacity allows us to conclude that a considerable increase (by 2-3 times) of the carrier state density near the Fermi level is taking place in the halogenated ceramics. The results of the fluorescent Cu Lalpha X-ray spectra correlate with these conclusions.