We report on the synthesis and measurements of the temperature dependence of resistivity, ρ(T ), the penetration depth, λ(T ), and upper critical magnetic field, Hc2(T ), for polycrystalline samples of dodecaboride ZrB12 and diboride MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the normal state with usual Bloch-Grüneisen temperature dependence of resistivity and with rather low resistive Debye temperature, TR = 280 K, for ZrB12 (as compared to MgB2 with TR = 900 K). The ρ(T ) and λ(T ) dependencies of these samples reveal a superconducting transition of ZrB12 at Tc = 6.0 K. Although a clear exponential λ(T ) dependence in MgB2 thin films and ceramic pellets was observed at low temperatures, this dependence was almost linear for ZrB12 below Tc/2. These features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state is possible in ZrB12. A fit to the data gives a reduced energy gap 2∆(0)/kBTc = 1.6 for MgB2 films and pellets, in good agreement with published data for 3D π -sheets of the Fermi surface. Contrary to conventional theories we found a linear temperature dependence of Hc2(T ) (Hc2(0) = 0.15 T ) for ZrB12.

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We have investigated the superconducting (T c ,J c ,H c2 ), electron transport, structural ͓x-ray diffraction ͑XRD͒, Rutherford backscattering spectrometry ͑RBS͔͒, and surface ͓x-ray photoelectron spectroscopy ͑XPS͒, ultraviolet photoelectron spectroscopy ͑UPS͔͒ properties of BaNbO 3Ϫx and Ba 2 Nb 5 O x epitaxial and oriented thin films grown on different substrates (Al 2 O 3 , NdGaO 3 , SrTiO 3 , and YSZ͒. Superconducting films with T c ϭ14 K and unusually high H c2 (0)ϭ28 T have been prepared on Al 2 O 3 substrates. At the same time, films on NdGaO 3 exhibit behavior similar to granular superconductors, while strong pure metal electron transport behavior of the films on 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.