Corrosion reactions of (YBa₂Cu₃O_7-x) and thallium barium calcium copper oxide (Tl₂Ba₂Ca₂Cu₃O_10+x) superconductor phases in aqueous environments

The chemical reactions leading to the decomposition of superconducting YBa₂Cu₃O_7x (0 > x > 0.05) in water solution and water vapor at different temperatures were investigated and the corrosion products were characterized using X-ray diffraction and scanning electron microscopy. Although the YBa₂Cu₃O₇-_xphase is stable in some nonaqueous solvents, it reacts readily with water, acids, carbon dioxide, and carbon monoxide. Samples of YBa₂Cu₃O₇-_x soaked in water solution at 25, 50, and 75 °C all produce BaCO₃ and CuO corrosion products as determined by X-ray powder diffraction studies. Although there is some evidence for the formation of small amounts of Y₂BaCuO₅ and Y₂O₃, the majority of the Y-containing corrosion products are produced as amorphous phases. Our studies suggest that“Y₂BaCuO₆”is formed with a metastable or distorted structure. Moreover, when YBa₂Cu₃O₇-_x was exposed to water vapor equilibrated at a temperature of 75 ¼ BaCO₃ forms and increases in amount with exposure time. On the other hand, CuO and “Y₂BaCuO₆”form only in the initial stages of corrosion. For comparison, superconducting Tl₂Ba₂Ca₂Cu₃O_10+x was also investigated, and similar results were obtained. Details related to the corrosion of these two high-T_c phases are discussed herein.