INFLUENCE OF COMPLEXING AGENTS ON PROPERTIES OF YBA2CU4O8 SUPERCONDUCTORS PREPARED BY THE SOL-GEL METHOD

A systematic study of sol-gel technique synthesized YBa2 CU4O8 (124) i s presented using six different complexing agents: ascorbic acid, citr ic acid, 1,2-ethanediol, poly(vinyl alcohol), succinic acid, and tarta ric acid. These complexing agents were found to influence significantl y the characteristics of both the precursors and the product supercond ucting material, in particular the homogeneity. The 124 phase was form ed by a solid state reaction at 780 degrees C in flowing oxygen after decomposition of the organic anions at lower temperature. The dried pr ecursor gels and final products were characterized by thermogravimetry , X-ray powder diffraction, scanning and transmission electron microsc opy, and magnetic susceptibility measurements. Syntheses using either 1,2-ethanediol or tartaric acid yielded monophasic YBa2Cu4O8 powder, w ith the highest diamagnetic volume fractions and superconducting trans ition temperatures (onset) at 79-80 K. (C) 1996 Academic Press, Inc.