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) is presented using six different complexing agents: ascorbic acid, citric acid, 1,2-ethanediol, poly(vinyl alcohol), succinic acid, and tartaric acid. These complexing agents were found to influence significantly the characteristics of both the precursors and the product superconducting material, in particular the homogeneity. The 124 phase was formed by a solid state reaction at 780 degrees C in flowing oxygen after decomposition of the organic anions at lower temperature. The dried precursor gels and final products were characterized by thermogravimetry, X-ray powder diffraction, scanning and transmission electron microscopy, and magnetic susceptibility measurements. Syntheses using either 1,2-ethanediol or tartaric acid yielded monophasic YBa2Cu4O8 powder, with the highest diamagnetic volume fractions and superconducting transition temperatures (onset) at 79-80 K. (C) 1996 Academic Press, Inc.