NICKEL DOPING IN Y2BA4CU7-XNIXO14- THE LOCATION OF NI IN THE STRUCTURE AND THE EFFECT ON SUPERCONDUCTIVITY(DELTA(247) )

Samples of Y2Ba2Cu7-xNixO14+delta have been prepared, with x up to 1.0 , using high pressure oxygen at 70 atmospheres and at a temperature of 1020 degrees C. X-ray diffraction of the products has revealed pure p hases; the cell parameters, determined by Rietveld analysis, show a sm all reduction in the orthorhombic distortion, and a large reduction in the c-axis, relative to the parent material. A.C. magnetic susceptibi lity measurements indicate fast suppression of the superconductivity, with a paramagnetic response observed with decreasing temperature for the x=1.0 sample. Preliminary EXAFS studies of the materials have been carried out and the initial analysis of the data implies that the nic kel shows a strong preference for the square-pyramidal sites in 247 st ructure.