EFFECT OF CU-CO AND COUPLED ER-CA CU-CO SUBSTITUTION UPON SUPERCONDUCTIVITY IN ERBA2CU3O7-DELTA/

The structural and superconducting properties of Cu-Co and coupled Er- Ca/Cu-Co substitution in ErBa2Cu3O7-delta have been studied using X-ra y diffraction, a.c. susceptibility, resistivity and oxygen, content me asurements. The oxides (Er1-yCay)Ba-2(Cu1-xCox)(3)O-z have been synthe sized for 0 less than or equal to x less than or equal to 0.15 and 0 l ess than or equal to y less than or equal to 0.45. The effect of incre asing the Co-concentration in ErBa2(Cu1-xCox)(3)O-z for 0 less than or equal to x less than or equal to 0.15 is to lower the carrier concent ration and decrease T-c, which is attributed to the hole filling by Co . This suppression in T-c has been compensated for by appropriate hole doping with Ca, in (Er1-yCay)Ba-2(Cu1-xCox)(3)O-2, which shows that f or a fixed Co-content T-c increases dramatically as the Ca-content inc reases, leading, for instance, to the oxide (Er0.55Ca0.45)Ba-2(Cu0.85C o0.15)(3)O-6.81 (to a T-c of 71 K), whereas the non-substituted phase ErBa2(Cu0.85Co0.15)(3)O-6.70 does not superconduct. As a result, the ' compensated oxide' (Er1-yCay)Ba-2(Cu1-xCox)(3)O-z exhibits an almost x -independent T-c ranging from 86 to 84 K for 0.12 less than or equal t o y = 3x less than or equal to 0.24. (C) 1996 Elsevier Science Limited .