SUPERCONDUCTING PROPERTIES OF NIOBIUM-DOPED Y-BA-CU-NB-O SUPERCONDUCTORS

Superconducting properties of the Y-Ba-Cu-Nb-O system of nominal compo sition YBa2Cu3-zNb(z)O(x), with 0 less-than-or-equal-to z less-than-or -equal-to 0.1, are being investigated by XRD, and measurement of d.c. electrical resistivity and magnetic susceptibility as a function of te mperature. XRD diffractograms showed the unambiguous existence of the YBa2NbO(y) cubic perovskite phase, besides the YBa2Cu3O(x) (YBCO) orth orhombic perovskite phase, for z > 0.03. The superconducting zero resi stivity temperature, T(c)O, of the system increased slightly with the increase of z, reaching the maximum at z = 0.02. The temperature at th e onset of Meissner effect, T(s)0, also indicated a similar enhancemen t. The enhancement in T(s)0 from the ZFC data was higher than that fro m the FC data. The introduction of Nb from the starting oxide of Nb2O5 probably improved the oxygen content of the YBCO phase, and subsequen tly enhanced the superconducting transition temperatures.