Sol-gel preparation and characterization of manganese-substituted superconducting YBa2(Cu1-xMnx)4O8 compounds

In this work the effect on the structural and superconducting properties of YBa2Cu4O8 (Y-124) of replacing Cu by Mn was studied. Multimetallic oxide powders with the composition of YBa2(Cu1-xMnx)(4)O-8 (x = 0.00. 0.01, 0.02, 0.03. 0.04 and 0.05) have been prepared by a simple aqueous sol-gel method at an oxygen pressure of I 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 was studied by thermogravimetry. Effects of manganese substitutions on the properties of compounds were studied by X-ray powder diffraction, TG analysis, IR spectroscopy and resistivity measurements. These data indicated that the transition temperature of superconductivity drastically decreases upon Mn substitution, and that superconductivity is lost at 3% of Mn substitution level. XRD measurements showed that the structure of the Y-124 phase is also largely affected even at low manganese-substitutional levels. (C) 2001 Elsevier Science Ltd. All rights reserved.