THE ELECTRON AND LATTICE PROPERTIES OF SUPERCONDUCTING CERAMICS YBCO-CL

A complex investigation of thermodynamic and structural characteristic s, NMR-spectra, Cu K XANES- and X-ray Cu Lalpha fluorescent spectra wa s carried out on the yttrium ceramics YBa2.01Cu2.92O6.54Cl0.61. The NM R-spectra of these HTSC have shown that the chlorine ions occupy three definite positions in the lattice of the starting yttrium ceramics. C omparison of these data with the neutron diffraction analysis results allowed us to estimate quantitative relations of the distribution of h alogen 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 chlor inated ceramics. In this connection some models, widespread in the lit erature, 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 dep endence of the heat capacity allows us to conclude that a considerable increase (by 2-3 times) of the carrier state density near the Fermi l evel is taking place in the halogenated ceramics. The results of the f luorescent Cu Lalpha X-ray spectra correlate with these conclusions.