Oxygen kinetics and superconductivity in the high-Tc oxide YBa2Cu3Ox

Disk-shaped samples of the nominal compositions YBa₂Cu ₃O₇, Y₂BaCuO₅ and BaCuO₂ were initially produced through the solid diffusion method. These samples were then cut into several small pieces, which were used for oxygen intercalation and desorption studies for temperatures between 330°C and 700°C. The compound YBa₂ Cu₃O_x went through a gradual transformation, going from the pure superconducting orthorhombic phase (x=7.0) to the pure semiconducting tetragonal phase (x=6.3). The compound BaCuO_y also varied its oxygen content, in the range 2.00<y<2.08. The compound Y₂BaCuO₅ did not allow any variation in its oxygen content, although small mass losses were measured. The critical temperature (T_c) for YBa₂Cu₃O_x shows a plateau around 70 K for 6.6<x<6.8, though a very sharp transition is observed for the parent sample (x=7.0) at T_c=93 K. It is argued that the plateau is related to a phase having a metastable configuration for the oxygen vacancies