NICKEL SUBSTITUTION IN LN(2)BA(4)CU(7-X)NI(X)O(14+DELTA) (LN = LANTHANIDE, YTTRIUM)

The system Ln(2)Ba(4)Cu(7-x)Ni(x)O(14-delta) (247), Ln = lanthanide, y ttrium, has been investigated by powder X-ray and neutron diffraction, thermogravimetric analysis and magnetic susceptibility measurements. Extended X-ray absorption fine structure (EXAFS) experiments at the Ni K-edge have been carried out on a number of the compounds. Results ha ve shown that, as with the related material YBa2Cu3O7-delta (123), nic kel doping takes place predominantly at the square pyramidal copper si tes, with some occupation at the square planar sites at low dopant lev els. A deterioration of the superconducting properties following intro duction of nickel content is observed. (C) 1998 Elsevier Science B.V.