The system Ln2Ba4Cu7−xNixO14+δ (247), Ln=lanthanide, yttrium, 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 have shown that, as with the related material YBa2Cu3O7−δ (123), nickel doping takes place predominantly at the square pyramidal copper sites, with some occupation at the square planar sites at low dopant levels. A deterioration of the superconducting properties following introduction of nickel content is observed.
Currie, D. B., & Weller, M. T. (1998). Nickel substitution in Ln2Ba4Cu7−xNixO14+δ: (Ln=lanthanide, yttrium). Physica C: Superconductivity and its Applications, 297(1-2), 95-102. https://doi.org/10.1016/S0921-4534(97)01854-6