Elsevier, Physica C: Superconductivity and its Applications, (504), p. 36-38, 2014
DOI: 10.1016/j.physc.2014.02.018
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We investigated superconducting (SC) properties of two layered titanium oxypnictides BaTi2Sb2O (Tc = 1.2 K) and BaTi2Bi2O (Tc = 4.6 K) being located in distinct SC phases in BaTi2(Sb1–xBix)2O by means of magnetic field dependence of electrical resistivities and magnetic susceptibilies. The SC parameter Hc2(0) and ξ0 for BaTi2Sb2O are determined to be 1.32 T and 158 Å. For BaTi2Bi2O, we obtained Hc1(0) = 0.006 T, Hc2(0) = 1.70 T, λ0 = 2900 Å, ξ0 = 139 Å, and κ = 20.8. The density of states (DOS) for BaTi2Bi2O at the Fermi level (4.79 states/eV/f.u.) is smaller than that for BaTi2Sb2O (5.7 states/eV/f.u.). The DOS change by the Bi-for-Sb substitution is in accordance with theoretical calculations but it cannot explain the enhanced Tc.