SOL-GEL SYNTHESIS AND CHARACTERIZATION OF SUPERCONDUCTING (Y1-XEUX)BA-2((CU1-YFEY)-FE-57)(4)O-8 SAMPLES

Superconducting powders with the composition of (Y1-xEux)Ba-2(Cu1-yFey )(4)O-8 have been prepared by a simple sol-gel method at an oxygen pre ssure of 1 atm starting from an aqueous mixture of the metal acetates. Homogeneous gels were achieved by complexing copper ions by tartaric acid before the gelation process. Thermal decomposition of the gels wa s studied by thermogravimetry and evolved gas analysis. Single-phase b ulk samples were obtained after annealing at 780 degrees C for 40 h. S tudies on the (Y1-xEux)Ba2Cu4O8 system confirmed that yttrium may be r eplaced by europium within the whole substitutional range (x=0.0-1.0). The lattice volume was expanded while the T-c was slightly decreased with the increasing europium content x. On the other hand, doping with iron both destabilizes the YBa2Cu4O8 phase and has a strong effect on its properties even at very low concentrations (y=0.01-0.05). Besides the XRD and SQUID measurements the samples were characterized by ther mal analysis for the oxygen stability and by Mossbauer spectroscopy fo r the hyperfine interactions around the Eu and Fe dopant ions.