Flux growth of superconducting La2CuO4 single crystals

We report here the first observation of superconductivity in lanthanum cuprate crystals grown in an ambient atmosphere. The best result achieved so far is: (1) superconducting transition temperature T-c = 32 K with DeltaT(c) similar to3 K by ac susceptibility measurement, and (2) T-c (on set) = 36 K and T-c (zero resistance) = 26 K by resistivity measurements. The solubility curve of La2CuO4 in molten CuO has been established, and large single crystals with size up to 16 x 15 x 0.1 mm(3) have been obtained. The morphology of the superconducting crystals (thin plate) is remarkably different from that of insulating crystals (pyramid), which suggests a layer growth mechanism. The mechanism produces an enlarged unit cell which permits O2- intercalation. This "soft" oxygenation has marked influence on the superconducting properties.