Intercalated hydrogen in yttrium barium cuprate: The state and mobility of a "guest" and modification of the "host" properties

The electric, magnetic, and physicochemical properties of yttrium barium hydrocuprate (H2YBa2Cu3O7) and its oxidized form (H2YBa2Cu3O7.8) are governed, to a large measure, by poorly studied behavior of hydrogen atoms in the lattice. The crystal chemical state and the mobility of a proton intercalated into yttrium barium cuprate have been investigated by the isotope exchange and inelastic neutron scattering techniques. By their behavior in the process of inelastic neutron scattering, a substantial fraction of protons can be considered mechanically free particles without chemical bonding with oxygen ions. The self-diffusion coefficient of a proton is estimated to be several orders of magnitude larger than that of oxygen ions, the latter coefficient being equal to 10(-13) cm(2) s(-1) at 490 K. Considerable changes in the lattice parameters and local charge distribution in the copper-oxygen subsystem are revealed by the x-ray powder diffraction analysis and nuclear quadrupole resonance (NQR). Discrete changes in the interplanar spacings along the c axis and in the Cu NQR frequencies with a gradual variation in the degrees of hydration and oxidation indicate the formation of hydrocuprate and (or) oxyhydrocuprate in the matrix of the initial material. (C) 2000 MAIK "Nauka/ Interperiodica".