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 room temperature. It was found that water adsorption subdivides into surface adsorption and bulk adsorption, which starts after the formation at the surface of a physically bound water layer no less than 65–100 Å thick. During bulk adsorption, H₂O molecules diffuse from this surface layer to the lattice, where they form four bound states with desorption temperatures of ～208, 330, 370, and 775°C and heats of formation of 38, 99, 72, and 68 kJ/mol, respectively, and mainly occupy interstitial sites of the intermediate layers. The presence of molecules in the lattice does not affect either the superconducting transition temperature or resistance to direct current; however, it results in an increase in the surface resistance. The resistance to direct current increases due to the formation of dielectric inclusions of other phases.