SUPERCONDUCTING BEHAVIOR OF TETRAGONAL CA1-CHI-CD-CHI-BALACU3O7-DELTA

We report our attempts to substitute increasing amounts of Cd for Ca in the 1113 high-T(c) phase CaBaLaCu3O7-delta (T(c) congruent-to 66 K). Single-phase superconducting Ca1-xCd(x)BaLaCu3O7-delta can be synthesized for x less-than-or-equal-to 0.6. However, the superconducting transition temperature falls from 66 to 21 K as x increases from 0 to 0.6. Attempts to synthesize Ca0.2Cd0.8BaLaCu3O7-delta or CdBaLaCu3O7-delta led to mixed-phase products with no evidence of any superconducting component indicating that the limit of stability for the superconducting phase with 1113-structure falls in the region 0.6 < x < 0.8. In view of the continuous fall in oxygen content upon incorporation of increasing amount of Cd in Ca1-xCd(x)BaLaCu3O7-delta, the superconducting behaviour of one particular composition Ca0.6Cd0.4BaLaCu3O7-delta has been studied in detail after annealing it in high p(O2) environment and reannealing it in ambient argon, and, lastly in ambient oxygen atmosphere. The results are compared with reference to the behaviour of Cd-free pure CaBaLaCu3O7-delta which was also given identical annealing treatments.