Decomposition behavior of high-Tc superconductor YBa₂Cu₃O_x in water

High-Tc superconductor - 6.8) reacts upon water to decompose. In order to clarify the process of decomposition, the microstructure of the YBC ceramics was studied by means of X-ray diffraction and EPMA after the reaction with water under autoclave and ambient conditions. Under the treatment in the autoclave above 100°C, the YBC ceramics were fully decomposed and Y(OH)₃ or YOOH, Ba²⁺ and CuO were found in the solution. Due to the EPMA study on the samples treated under ambient conditions, three regions were confirmed in the grains: a) the inner core region without any interaction with water, b) the intermediate region of low Ba content surrounding the core, and c) the surface layer containing Y and Cu in the molar ratio Y/Cu=l/3 and very little amount of Ba. On these basis, it is concluded that the decomposition of the YBC ceramics is due to the diffuse-out of Ba cations to water and that the decomposition is not accompanied by the formation of Y₂BaCuO₅ phase.