Chemical and Electrochemical Processes that Accompany the Degradation of HTSC Materials

1 Chemical and Electrochemical Processes that Accompany the Degradation of HTSC Materials 

Attention is usually focused on degradation phenomena that are caused by interaction with water (including atmospheric moisture) and carbon dioxide. Regarding interactions with water, YBCO and its substituted derivatives are the most active [457-460]. Their hydrolysis leads to the formation of a number of ions, including unstable aquacomplexes of Cu which react with water evolving oxygen. In a small volume of water or a moist atmosphere solid products are accumulated, and the process as a whole is usually represented as 

Y2BaCuOs can be subsequently hydrolyzed with the formation of Y(OH)3 [461]. In the presence of CO2 or CO (which is also oxidized by Cu , BaaCOa is formed [462]. 

The rate of degradation of YBCO depends substantially on the impurity content and the sample s prehistory, as well as on the porosity, grain size, and other macro-structural factors [468]. Surface contamination by carbon-containing particles substantially accelerates intractions with water [469]. Inner stresses in the samples also have a certain effect on these processes [470]. As a rule, high-quality HTSC films are more stable to degradation than the corresponding ceramics [453]. 

The degradation processes of other HTSCs are by and large similar, even if slower, and are generally characterized by their preferential depletion of alkaline-earth components with the formation of the corresponding hydroxides and carbonates [468, 471]. The stability rows discussed sometimes [28] are, as a rule, of a limited application, and the position of HTSC oxides in them depends substantially on the nature of the medium and the interaction conditions [417]. 

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