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

The electric, magnetic, and physicochemical properties of yttrium barium hy drocuprate (H2YBa2Cu3O7) and its oxidized form (H2YBa2Cu3O7.8) are governed , to a large measure, by poorly studied behavior of hydrogen atoms in the l attice. The crystal chemical state and the mobility of a proton intercalate d into yttrium barium cuprate have been investigated by the isotope exchang e and inelastic neutron scattering techniques. By their behavior in the pro cess of inelastic neutron scattering, a substantial fraction of protons can be considered mechanically free particles without chemical bonding with ox ygen ions. The self-diffusion coefficient of a proton is estimated to be se veral orders of magnitude larger than that of oxygen ions, the latter coeff icient 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 a long the c axis and in the Cu NQR frequencies with a gradual variation in t he degrees of hydration and oxidation indicate the formation of hydrocuprat e and (or) oxyhydrocuprate in the matrix of the initial material. (C) 2000 MAIK "Nauka/ Interperiodica".