RELATION BETWEEN CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY IN LA2-XBIXCUO4+DELTA WITH EXCESS OXYGEN

The relation between the crystal structure and superconductivity has b een investigated for La2-xBixCuO4+delta with excess oxygen, in which t he phase separation observed in La2CuO4+delta is suppressed. In the ra nge of 0.03 less than or similar to delta less than or similar to 0.1 and T less than or similar to 100 K, the crystal structure is orthorho mbic for x = 0.05, while it is tetragonal for x = 0.10. With increasin g delta, T-c increases and then reaches the maximum value, 20 - 25 K, at delta greater than or similar to 0.05 for 0.05 less than or equal t o x less than or equal to 0.10, independent of the crystal structure. The overall symmetry of the crystal structure is concluded not to be s o responsible for the appearance of high-T-c superconductivity.