Effect of Cu-Ga and coupled Nd-Ca/Cu-Ga substitution on the superconductivity of NdBa2Cu3O7-delta

The structural and superconducting properties of (Nd1-yCay)Ba-2(Cu1-xGax)(3 )O-z samples have been studied by x-ray diffraction, resistivity, ac suscep tibility and oxygen content measurements. The effect of increasing the Ga c oncentration in NdBa2(Cu1-xGax)(3)O-z reduces the orthorhombicity without m uch disturbing the oxygen-vacancy order. This is accompanied by an increase in the normal state resistivity and decreases in both the carrier concentr ation and T-c, which is attributed to hole filling by Ga. This suppression of T-c has been compensated by appropriate hole doping with Ca in (Nd1-yCay )Ba-2(Cu1-xGax)(3)O-z, which shows that for a fixed Ga content T-c increase s dramatically as the Ca content increases. For instance, in the oxide (Nd1 -yCay)Ba-2(Cu0.94Ga0.06)(3)O-z, the T-c increases from 0 K (y = 0.0, semico nductor) to 76 K (y = 0.36 compensated oxide) as the hole filling by Ga is nearly balanced by hole doping from Ca.