IN-SITU X-RAY MEASUREMENTS OF OXYGEN-OUT DIFFUSION IN YBA2CU3O7-DELTATHIN-FILMS

In order to change the oxygen content of YBa2Cu3O7-delta thin films, w e have measured the YBCO c-axis length ''in situ'' by X-ray analysis w hile heating the films in a flow of 10 mbar of molecular oxygen. We ob served two kinds of c-axis length variation: a reversible one associat ed with the temperature and composition independent expansion coeffici ent which was determined to be alpha(c) = 23 . 10(-6) K-1, and an irre versible variation that appeared when the substrate was heated above 2 00 degrees C. The latter is attributed to oxygen loss. The timescale o f the oxygen effusion strongly depends on the morphology of the YBa2Cu 3O7-delta-film, i.e. films with rough surface loose oxygen much quicke r than smooth films. Therefore, in order to obtain films in a controll ed way, it is necessary to observe the c-axis length continuously duri ng the preparation. The c-axis length and the superconducting critical temperature are used to determine the oxygen deficiency delta. Copyri ght (C) 1996 Published by Elsevier Science Ltd.