Effect of Mo and Mo-Ca substitution on the superconductivity of GdBa2Cu3O7-delta

The structural and superconducting properties of (Gd1-yCay)Ba-2(Cu1-xMox)(3 )O-2 samples are investigated using X-ray diffraction, A.C. susceptibility, electrical resistivity End oxygen content measurements. The effect of incr easing the Mo concentration in GdBa2(Cu1-xMox)(3)O-z changes the structure from orthorhombic to tetragonal, accompanied by an increase in the normal s tale resistivity and decreases both the oxygen content and T-c, which is at tributed to hole filling by Mo. This suppression in T-c has been compensate d for by appropriate hole doping with Ca, for instance in the oxide (Gd1-yC ay)Ba-2(Cu0.92Mo0.08)(3)O-z, the T-c increases from 27 K (y = 0.0) to 86.5 K (y = .24, compensated oxide), closer to the value of 91 K for pure GdBa2C u3O7 - delta due to the balance between the hole filling by Mo and hole dop ing by Ca. (C) 1999 Elsevier Science Ltd. All rights reserved.