Superconducting and anomalous electron transport properties and electronic structure of BaNbO3-x and Ba2Nb5Ox films

We have investigated the superconducting (T_c,J_c,H_c2), electron transport, structural [x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS)], and surface [x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS)] properties of BaNbO_3-x and Ba₂Nb₅O_x epitaxial and oriented thin films grown on different substrates (Al₂O₃, NdGaO₃, SrTiO₃, and YSZ). Superconducting films with T_c=14 K and unusually high H_c2(0)=28 T have been prepared on Al₂O₃ substrates. At the same time, films on NdGaO₃ exhibit behavior similar to granular superconductors, while strong pure metal electron transport behavior of the films on SrTiO₃ was observed. XPS and RBS investigations show that the composition of these films is almost the same, while UPS study evidenced the Fermi edge position corresponding to semimetallic behavior of the films for all substrates.