The environmental degradation mechanism and protective organic thin film coatings on a high-temperature bismuth-cuprate superconductor

The degradation mechanism for Bi2Sr2CaCu2Ox (Bi-2212) in a highly humid air has been investigated. Using diffuse reflectance infrared Fourier transfor m spectroscopy, different reaction steps for carbonate formation with aging time were found to occur on the surface of the superconductors. During the initial stage, the calcium carbonate species mainly formed due to the pref erred hydration of calcium ions because of their lower ionic-dipole interac tion energy. At a later stage, the strontium carbonate species became the m ore dominant species because of the kinetics of this step along with the hi gher molar ratio of Sr2+ to Ca2+. In addition to the carbonates, larger amo unts of Sr(OH)(2). nH(2)O (n = 1 or 8) and CuBi2O4, along with relatively s mall amounts of Ca(OH)(2) were also found on the surface along with Sr(OH)( 2). The formation of larger amounts of strontium-related degradation produc ts also led to larger amounts of Bi2CuO4 being formed. The effect of steari c acid coating on the degradation of the superconductor was also investigat ed with respect to long term durability in a very humid atmosphere. These c oatings strongly prevented the formation of carbonates on the surface of (B i,Pb)(2)Sr2Ca2Cu3Oy (Bi,Pb-2223). Strong complex bonds between the carboxyl ate groups of the organic acids and the metal ions on the surface of the su perconductor were formed, which helped to retard the degradation process fo r the superconducting phase. (C) 2001 Elsevier Science B.V. All rights rese rved.