Superconducting and anomalous electron transport properties and electronic structure of ${\mathrm{BaNbO}}_{3-x}$ and ${\mathrm{Ba}}_2{\mathrm{Nb}}_5{\mathrm{O}}_x$ films

We have investigated the superconducting ${(T}_c{,J}_c{,H}_{c2\mathrm{}}),$ electron transport, structural [x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS)], and surface [x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS)] properties of ${\mathrm{BaNbO}}_{3-x}$ and ${\mathrm{Ba}}_2{\mathrm{Nb}}_5{\mathrm{O}}_x$ epitaxial and oriented thin films grown on different substrates $({\mathrm{Al}}_2{\mathrm{O}}_3,$ ${\mathrm{NdGaO}}_3,$ ${\mathrm{SrTiO}}_3,$ and YSZ). Superconducting films with $T_c=14\mathrm{}\hspace{0.5em}\mathrm{K}$ and unusually high $H_{c2\mathrm{}}\mathrm{}\left(0\right)=28\mathrm{}\hspace{0.5em}\mathrm{T}$ have been prepared on ${\mathrm{Al}}_2{\mathrm{O}}_3$ substrates. At the same time, films on ${\mathrm{NdGaO}}_3$ exhibit behavior similar to granular superconductors, while strong pure metal electron transport behavior of the films on ${\mathrm{SrTiO}}_3$ 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.