The c-axis length was measured  in situ, by means of X-ray analysis, while heating the films in a flow of 10mbar of molecular O. Two types of c-axis length variation were observed. One was a reversible variation that amounted to 2.3 x 10-5/K, and the other was an irreversible variation that appeared when the substrate was heated above 200C. The latter was attributed to O loss. It was found that the time-scale of the O effusion depended strongly upon the morphology of the film. Thus, films with rough surfaces lost O much quickly than did smooth films.

M.Stenger, G.Ockenfuss, M.Reese, T.Königs, R.Wördenweber, C.Barre, J.Y.Prieur, J.Joffrin: Solid State Communications, 1996, 98[9], 777-80