Superconductivity at 40 K in the Oxygen-Defect Perovskites La 2- x Sr x CuO 4- y

Abstract

Structural, magnetic, and electronic properties of compounds in the series La_2-xSr_x CuO_4-y for 0.05 ≤ x ≤ 1.1, with δx = 0.025, were studied. Resistance, susceptibility, Meissner, and shielding measurements have revealed superconductivity among several members of the series. For x = 0.15, the transition temperature T_c, measured at the midpoint of the resistive transition, is a maximum at 39.3 K with a width of 2 K. At other compositions the transition is broader and occurs at a lower temperature. Annealing the x = 0.15 sample in oxygen at 500°C increases T_c to 40.3 K, while annealing at the same temperature under vacuum suppresses the superconductivity. These changes in oxygen content and T_c are reversible.