EFFECT OF SOME TRANSITION-ELEMENTS ON THE SUPERCONDUCTIVITY OF YBA2CU3O6+Y CERAMIC

In order to seek the influence of several transition metals such as Cr , Mn and Ni on the superconductivity of YBa2Cu3O6-y, a systematic stud y of structural and superconducting properties of Cr, Mn and Ni-doped YBaCuO powders and of the high T-c compound YBa2(Cu1-x M-x)(3)O6+y has been performed, where M = Cr, Mn, Ni and x = 0.00; 0.02; 0.05 and 0.1 0. X-ray powder diffraction and a.c susceptibility measurements have b een made. The doping elements do not significantly modify the YBaCuO c ell parameters, with the exception of 10% NiO. In doped samples, super conducting phases with T-c of 83 K and 60 K are often detected with X- ray patterns resembling the YBaCuO ones. This might correspond to a pr eferential substitution of Cr, Mn and Ni on particular sites in the YB aCuO lattice. If we compare the structural and superconducting propert ies of doped samples and substituted ones, we can say that Cr, Mn and Ni have been substituted on Cu sites and that Cu has a major role in t he high T-c of YBaCuO oxide since all samples show a depression in T-c values.