POSSIBILITY OF THE EXISTENCE OF FULLY OXYGENATED SUPERCONDUCTING YBACUO FILMS WITH A TETRAGONAL STRUCTURE

YBaCuO thin films were deposited in situ on LaAlO3 single-crystal subs trates by sputtering of a stoichiometric Y1Ba2Cu3O7 target. These film s were studied combining ion beam analysis (IBA) techniques with X-ray diffraction measurements at room temperature. Depending on the sample cooling conditions (cooling rate, oxygen pressure), the similar to 50 00 Angstrom thick; YBaCuO films can exhibit either an orthorhombic twi n phase or a quasi-tetragonal structure. The former is obtained by low cooling rates at high oxygen pressure (0.2-1 bar), whereas the latter needs a rapid quenching to room temperature, even at low oxygen press ures. Our IBA oxygen content measurements show that both kind of sampl es are fully oxygenated (similar to O-7) YBaCuO compounds with T-c ons et of 91 K. Moreover, He-4(+) channeling studies show that the minimum yield chi(min)(Ba) for the quasi-tetragonal films increases with the beam energy. This result seems to indicate that the crystal lattice of these quenched films is subject to some kind of internal strains. Fro m these observations and following thermodynamical considerations. we consider that the formation of YBaCuO thin films with fully oxygenated (similar to O-7) tetragonal structure takes place indeed during the h igh temperature in situ growth by cathodic sputtering and these featur es can be preserved by means of a rapid quenching to room temperature.