SUPERCONDUCTIVITY OF LA2-XNDXCUO4+Z PREPARED UNDER HIGH OXYGEN-PRESSURE - SUPPRESSION OF THE PHASE-SEPARATION SEEN IN LA2CUO4+Z

La2-xNdxCuO4+z was prepared under oxygen pressures ranging between 0.2 bar and 60 kbar. The oxygen content increased slightly as the Nd content increased; z {reversed tilde equals} 0.09 for x = 0.4 under 60 kbar of oxygen. The Nd substitution and the introduction of excess oxygen as oxide ion counteract each other from the viewpoint of structure chemistry. For La2CuO4+z the superconducting transition temperature, Tc, was almost independent of z at around 40 K, while the Tc of the Nd-doped samples showed a strong dependence. The superconductive volume fraction was considerably increased by the Nd doping. The phase separation into the nearly stoichiometric (z {reversed tilde equals} 0) semiconductive phase and an oxygen-rich superconductive phase as seen in La2CuO4+z may be suppressed by the Nd-for-La substitution. © 1991.