EFFECT OF NONSTOICHIOMETRY AND CE-DOPING ON THE TETRAGONAL SUPERCONDUCTING PHASE CABALACU3O7-DELTA

We have synthesized CaBaLaCu3O7-delta and related compounds Ca0.9BaLaCu3O7-delta, Ca11 BaLaCu3O7-delta and Ca0.9Ce0.1 BaLaCu3O7-delta in order to investigate the effect of doping and non-stoichiometry at Ca-sites on the superconducting behaviour of tetragonal superconductor CaBaLaCu3O7-delta. The superconducting transition temperature (T(c)) of Ca0.9 BaLaCu3O7-delta is the same as that of pure CaBaLaCu3O7-delta(67 +/- 1 K). Calcium excess compound Ca1.1 BaLaCu3O7-delta showed an enhancement in T(c) to 72 K while the cerium-substituted compound Ca0.9 Ce0.1 BaLaCu3O7-delta showed a drop in T(c) to 43 K. The results are explained on the basis of difference in valency between the host and the dopant ion.