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

Structural, magnetic, and electronic properties of compounds in the series La2-xSrx CuO4-y for 0.05 </= x </= 1.1, with deltax = 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 degrees 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.

Superconductivity and Antiferromagnetism in Boron-Rich Lattices

Ferromagnetism, antiferromagnetism, or superconductivity has been discovered in most hexa- and dodecaborides.

Superconducting Gallium Antimonide

A metallic phase of gallium antimonide, obtained by quenching at approximately 120 kilobars to 77 degrees K and then releasing pressure, is a superconductor. The transition temperature depends on the annealing conditions; for samples annealed at 250 degrees C under pressure before quenching, it is 4.24 degrees +/- 0.10 degrees K, and H(c2) (the critical field) equals 2640 gauss at 3.50 degrees K. This temperature is higher than the 2.1 degrees K reported for metallic indium antimonide.