ENHANCEMENT OF T-C BY SUBSTITUTING STRONTIUM FOR BARIUM IN THE YBA2CU4O8 SUPERCONDUCTOR PREPARED BY A SOL-GEL METHOD

In order to study the influence of strontium substitution on YBa2Cu4O8 , two series of samples with composition Y:Sr:Ba:Cu = 1 - x:x:2:4 and Y:Ba:Sr:Cu = 1:2 - 2x:2x:4 (x = 0.0-1.0) were synthesized by a simple aqueous sol-gel method at 1 atmosphere oxygen pressure. Effects of str ontium substitutions on the properties of the compounds were studied b y thermogravimetric analysis, X-ray powder diffraction, scanning elect ron microscopy and resistivity measurements. It was unambiguously demo nstrated that in both series strontium enters the structure at the bar ium positions. Nearly single-phase Y(Ba1-xSrx)(2)Cu4O8 superconducting samples for x = 0.0-0.3 were obtained, when final heat treatment was carried out at 835 degrees C for 70 h in flowing oxygen atmosphere. Th e critical temperature of the Y(Ba1-xSrx)(2)Cu4O8 is enhanced to 88 K at about 20% Sr substitution. (C) 1998 Published by Elsevier Science B .V. All rights reserved.