Europium substitution effects in superconducting YBa2Cu4O8 synthesized under one atmosphere oxygen pressure

Y1-xEuxBa2Cu4O8 powder samples, with x=0, 0.25, 0.5, 0.75, and 1.0, were synthesized at ambient pressure using either an acetate-tartrate sol-gel method or a LiF flux process. The lattice parameters and purity of the samples were checked using X-ray diffraction. The superconducting transition was monitored by magnetic-susceptibility measurements. Replacing yttrium with europium increased the unit-cell volume, decreased the orthorhombicity (b/a) and the critical temperature. The hyperfine interactions at the europium site were studied by Eu151 Mössbauer spectroscopy. The complete quadrupole Hamiltonian of the 21.5-keV γ transition of Eu151 was successfully applied in the analyses of the Mössbauer spectra. The Mössbauer parameters obtained were found to resemble those measured for the EuBa2Cu3Cu3O7-δ (1:2:3) system. It was demonstrated that magnetic alignment of the crystallites could not be obtained with an 11.7-T field, contrary to the 1:2:3 and other high-Tc systems. The magnetic susceptibility for 1:2:4 single crystals appears to be isotropic.