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 purit y of the samples were checked using x-ray diffraction. The superconduc ting transition was monitored by magnetic-susceptibility measurements. Replacing yttrium with europium increased the unit-cell volume, decre ased the orthorhombicity (b/a) and the critical temperature. The hyper fine interactions at the europium site were studied by Eu-151 Mossbaue r spectroscopy. The complete quadrupole Hamiltonian of the 21.5-keV ga mma transition of Eu-151 was successfully applied in the analyses of t he Mossbauer spectra. The Mossbauer parameters obtained were found to resemble those measured for the EuBa2Cu3O7-delta (1:2:3) system. It wa s demonstrated that magnetic alignment of the crystallites could not b e obtained with an 11.7-T field, contrary to the 1:2:3 and other high- T(c) systems.