FORMATION OF YBA2CU3O7 TETRAGONAL PHASE BY RAPID COOLING OF THIN-FILMS GROWN BY CATHODIC SPUTTERING

YBa2Cu3O7-delta (YBaCuO) thin films were prepared in situ by cathodic sputtering of stoichiometric target onto LaAlO3 or MgO single crystal substrates, After deposition some samples were cooled down quickly (hu ndreds degrees/min) till room temperature under 0.35 mbar or 1 bar of O-2, in order to preserve the original oxygen content and the structur e of the films during the in situ growth. Reference samples were coole d down slowly (similar to 3 degrees C/min, 1 bar of O-2), at optimized conditions. The composition, electrical and magnetic properties and m icrostructure of YBaCuO films were studied ex situ at room temperature , Both slowly and rapidly cooled samples at 1 bar of O-2 show good phy sical properties with values of T-c(rho = 0) approximate to 87 K, surf ace resistance R(s)(measured at 77 K, 10 GHz) approximate to 1 m Omega and J(c)(T = 5 K, zero field) approximate to 2 x 10(7) A/cm(2) The ra pidly cooled sample at low oxygen pressure shows high T-c value but si gnificant degradation of R(s) is observed, Our direct oxygen content m easurements using recently developed Ion Beam Analysis (IBA) technique s show that both kind of films are fully oxygenated (O-7+/-0.3) YBaCuO compounds. The combination of X-ray Diffraction (XRD) and Transmissio n Electron Microscopy (TEM) measurements indicates the majority presen ce, in the case of the rapidly cooled films, of a disordered tetragona l phase, with lattice parameters a = b = 3.86 Angstrom and c = 11.690 Angstrom, whereas for the slowly cooled samples the dominant structure is orthorhombic, with a = 3.82 Angstrom, b = 3.88 Angstrom and c = 11 .686 Angstrom. It is concluded that fully oxygenated YBaCuO tetragonal phase is growing during cathodic deposition.