CRYSTAL-STRUCTURE, OXYGEN STOICHIOMETRY AND SUPERCONDUCTING PROPERTIES OF GDBA2-XSRXCU3O7-DELTA LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1.6)

The dependence of crystal structure, oxygen content and T-c of ceramic GdBa2-xSrxCu3O7-delta (0.0 less than or equal to x 1.6) samples on th ree different sets of annealing conditions was investigated. For sampl es annealed in oxygen at 900 degrees C, a decrease of T-c and orthorho mbicity was observed with increasing Sr content. However, either annea ling these samples in argon al, or quenching in air from 900 degrees C , prior to annealing in oxygen at 500 degrees C, leads to an enhanceme nt of T-c and orthorhombicity for 0 < x < 1.6. The oxygen non-stoichio metry (delta) varied in the range 0 < delta < 0.12 for all the samples . The AC susceptibility as a function of temperature and DC bias field was studied for some selected samples. The irreversibility line was d etermined for x = 0.0 and 1.0 samples annealed under three different c onditions. Further, for the x = 1.0 sample, the influence of annealing at different temperatures in oxygen on the structure, oxygen content and T-c was studied. The present study showed that substitution of Ba by Sr leads to a complex order-disorder behavior of the oxygen sub-lat tice, depending on the annealing conditions.