Study of the relation between composition and physical properties of YBaCuO thin films using RBS, NRA, XRD, XAS and ϱ( T)

Abstract

Superconducting YBaCuO thin films with various oxygen contents were prepared by inverted cylindrical magnetron sputtering of a stoichiometric YBaCuO target on a MgO single crystal heated to about 750°C. The samples were cooled to room temperature either (i) at p o 2 = 0.25 mbar or (ii) at p o 2 = 1 atm.As-grown samples were characterized by ϱ( T) measurements ( T c, Δ T c). The film composition was determined by Rutherford backscattering spectrometry (RBS) in random and channeling geometries, nuclear reaction analysis (NRA) and X-ray diffraction (XRD). The oxygen content, directly measured by RBS and NRA, were compared to that deduced from the c-axis lattice parameter. While for the (i) samples a difference is observed between RBS and XRD results, the latter being inconsistent with both T c and the oxygen content, for the (ii) samples, a good agreement is found. The copper oxidation state was controlled by X-ray absorption spectroscopy (XAS) of the CuL 2,3 edge operated in the total electron yield mode. The results show that for the as-grown YBaCuO films only the Cu(II) state is present. The effect of long temperature annealings in 18O 2 and 16O 2 atmospheres ( T = 650°C, t = 19 h) was also studied. The results are discussed.