Out- and in-diffusion of oxygen in YBa2Cu3O7 - x oxide

In situ resistance measurements have been used to investigate the oxygen out- and in-diffusion in YBa2Cu3O7 - x oxide. The oxygen content has been measured by nuclear reaction and by weighing; X-ray diffraction has been used to determine the crystalline structure. Polycrystalline sintered material has been used. Out-diffusion has been investigated by heating samples with x = 0.1 in argon atmosphere at fixed temperature and as a function of the time. The resistance increases exponentially and reaches saturation after 5000 min at 550 °C. The oxygen content, after an initial decrease which occurs in the first 100 min, remains constant. Order-disorder transformation can be responsible for the exponential increase in resistance. The in-diffusion has been studied with a material having x = 0.65 heated in oxygen. As a function of the time the resistance curves continuously decrease and present two slopes: fast at the beginning and slow after a certain time. At first the material is tetragonal and non-superconducting. The sharp decrease in resistivity can be attributed to the presence of a thin continuous conductive skin around the grain or, more likely, to a disorder-order transformation activated by the presence of oxygen and involving a large part of the material. © 1989.