Oxygen kinetics and superconductivity in the high-Tc oxide YBa/sub 2/Cu/sub 3/O/sub x/

Disk-shaped samples of the nominal compositions YBa/sub 2/Cu/sub 3/O/sub 7/, Y/sub 2/BaCuO/sub 5/, and BaCuO2, were initially produced through the solid diffusion method. Following, these samples were cut into several small pieces, which were then used for oxygen intercalation and desorption studies, in temperatures between 330 0C and 700 0C. The compound YBa/sub 2/Cu/sub 3/O/sub 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/sub y/ also varied its oxygen content, in the range 2.00<y<2.08. The compound Y/sub 2/BaCuO/sub 5/ didn't allow any variation in its oxygen content, although small mass losses were measured. The critical temperature (T/sub c/) for YBa/sub 2/Cu/sub 3/O/sub 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/sub c/=93 K. The authors argue that the plateau is related to some phase having a metastable configuration for the oxygen vacancies