STUDY OF OXYGEN-CONTENT AND OF DISORDER IN YBACUO THIN-FILMS WITH ENLARGED C-AXIS LATTICE-PARAMETER

It was recently shown that YBaCuO thin films prepared at low oxygen pa rtial pressure p(O2) present enlarged c-axis lattice parameter. In thi s paper, we report on further results concerning the c-axis expansion effect, but on films produced at particular conditions: they were depo sited at relatively high p(O2) = 0.25 mbar and then cooled to RT at th e same oxygen partial pressure. A question arises: are these films ful ly oxidized or are they oxygen deficient films, according to the relat ionship between the c-axis parameter and the oxygen content? YBaCuO th in films were deposited, on MgO single crystal heated to about 750-deg rees-C, by inverted cylindrical magnetron sputtering of a stoichiometr ic Y1Ba2Cu3O7 target, at an oxygen partial pressure p(O2) = 0.25 mbar. A series of samples was cooled down to room temperature at the same p ressure (0.25 mbar) and a second one, at higher pressure (I atm). As g rown samples were characterized by p(T) resistivity measurements (T(C) , DELTAT(C)). Their composition and structure were studied by Rutherfo rd Backscattering Spectrometry (RBS) in random and channeling geometri es, nuclear Reaction Analysis (NRA), X-ray Diffraction (XRD) and Raman Spectroscopy. The oxygen contents, measured by RBS and NRA, were comp ared to those deduced from XRD (c-axis parameter). A good agreement wa s found for the YBaCuO films cooled at 1 atm, but significantly higher results were obtained by RBS and NRA for the films cooled at 0.25 mba r. These results suggest that the cooling at low oxygen partial pressu re leads to the formation of films with enlarged c-axis parameter, but with T(C) values similar to those observed for the samples cooled at p(O2) almost-equal-to 1 atm (T(C) almost-equal-to 88 K). The results a re discussed.