Co and Fe substitution in YBa2Cu3O7−δ

Abstract
The limiting substitution of Co or Fe for Cu in the orthorhombic superconducting phase YBa2Cu3O7−δ yields the tetragonal, semiconducting compositions YBa2Cu2CoO7.25 and YBa2Cu2.5 Fe0.5O7.19 after annealing at 400°C and slow cooling in O2. Single-crystal x-ray structural analyses, conductivity and magnetic-susceptibility measurements, and thermogravimetric analysis (TGA) data provide evidence for Co or Fe substitution at the Cu (1) position and intercalation of peroxide ions (O2)2− The two compositions decompose for disintercalation of oxygen beyond O6.7 for Co and O6.4 for Fe when heated in N2. The Cu(2) atoms of tetragonal YBa2Cu4O6 appear to be antiferromagnetic below a Tn ∼ 240 K, which is similar to comparable Cu–O planar nets in stoichiometric La2CuO4.