HIGH-PRESSURE SYNTHESIS OF THE SR2CUO3+DELTA SUPERCONDUCTOR OBSERVATION OF AN INCREASE IN TC FROM 70-K TO 94-K WITH HEAT-TREATMENT

The high-T(c) ceramic superconductor Sr2CuO3+delta was synthesized at high oxygen pressure (5.7 GPa) and stabilized in the tetragonal-layered structure. Details are reported for the synthesis conditions and the superconducting properties. The as-prepared material had an onset T(c) at 70 K which could be increased to 94 K by heat treatment in N2 at 310-degrees-C for 1 h or at 240-degrees-C for 12 h. Data are reported for the effect of post-synthesis heat treatment on superconducting properties, lattice parameters and weight-loss characteristics. A weight loss was detected above 310-degrees-C which correlated with a deterioration in superconducting properties. The material was found to be non-superconducting when heat treated at 450-degrees-C, even though the structure remained in t tetragonal structure. Conversion to the orthorhombic low-pressure state occurred at a higher temperature, and was complete by 760-degrees-C. The results are discussed in terms of a possible oxygen-doping mechanism for the bimetallic superconductor Sr2CuO3+delta.