Effect of Y-doped NbB_2.5 on structural and superconducting properties

The crystal structure and magnetic properties of Nb_1−xY_xB_2.5 with 0.000 ≤ x ≤ 0.050 compositions are reported. Rietveld refinement of XRD patterns shows that the partial substitution with yttrium atoms in niobium sites increases the unit cell volume. Magnetization measurements show that the critical temperature (T _c) changes from 9.0 K to 9.9 K for x = 0.000 and x = 0.050, respectively. Using the XPS measurements, the Nb 3d and B 1s core levels were identified, and the XPS valence band of XPS was measured. Our results show an increase in the valence band at zero eV as the yttrium content increases, which might be related to the T _c change. The electron-phonon coupling constant was calculated from the McMillan equation; our results indicate that the Nb_1−xY_xB_2.5 compounds are weak-coupled superconductors. Our work stablishes the effect of light doping on the structure and physical properties of these superconductors. (paper)