Adsorption of water molecules on yttrium barium cuprate superconductors

Gravimetry and thermogravimetric analysis were used to study the adsorption of water molecules on the high temperature superconductor YBa2Cu3O7 at roo m temperature. It was found that water adsorption subdivides into surface a dsorption and bulk adsorption, which starts after the formation at the surf ace of a physically bound water layer no less than 65-100 Angstrom thick. D uring bulk adsorption, H2O molecules diffuse from this surface layer to the lattice, where they form four bound states with desorption temperatures of similar to 208, 330, 370, and 775 degrees C and heats of formation of 38, 99, 72, and 68 kJ/mol, respectively, and mainly occupy interstitial sites o f the intermediate layers. The presence of molecules in the lattice does no t affect either the superconducting transition temperature or resistance to direct current; however, it results in an increase in the surface resistan ce. The resistance to direct current increases due to the formation of diel ectric inclusions of other phases. (C) 2000 MAIK "Nauka/Interperiodica".