EFFECT OF CU-SITE CO, NI AND GA SUBSTITUTION ON THE SUPERCONDUCTIVITYOF TETRAGONAL LABACACU3O7 SYSTEM

X-ray diffraction and AC susceptibility measurements have been carried out on LaBaCaCu3-xMxO7 (RE:1113) system, where M = Co, Ni, Ga with x = 0.0, 0.06, 0.08, 0.24 and 0.30. X-ray diffraction results show that these cations substitute isostructurally in the tetragonal La:1113 pha se, with decreased c-parameter for Co and Ga and nearly unchanged for Ni, at least up to 10 at% of doping level. Superconducting transition temperature (T-c) of the pristine sample, determined from the measurem ents of both real and imaginary parts of AC susceptibility, decreases with an increase of x for all the three cations. T-c depression rate w ith doping concentration (dT(c)/dx) follows the order Ga > Ni > Co. Th ese results, in terms of T-c depression due to these impurities in the parent La:1113 system are similar to those observed for RE:124 (REBa2 Cu4O8), 247 and Nd:214 (Nd2-xCexCuO4) compounds, but are different fro m RE:123 and La:214. (C) 1998 Published by Elsevier Science B.V. All r ights reserved.