Superconductivity of La2−ySryCu1−xNixO4+δ (y = 0.1, 0.2; 0⩽x⩽0.5) The hole-compensating effect of Ni

Magnetization measurements below 50 K on ceramic La2−y Sr y Cu1−x Ni x O4+δ (y = 0.1, 0.2; 0⩽x⩽0.5) show a progressive diminution of superconducting properties with increasing x. The larger suppressive action of Ni in the y=0.1 system than that for y=0.2 is attributed to the hole-compensating effect of Ni3+. The assumption that nickel is in the 3+ state satisfactorily explains: (1) the reduction in hole concentration, (2) a right-shift of the T c versus y curve with x, and (3) the low magnetic moment carried by Ni atoms, in the La2−ySryCu1−xNixO4+δ system.