CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY IN LA1.95BI0.05CUO4-SOLUTION(DELTA OXIDIZED BY A KMNO4 AQUEOUS)

We have obtained La1.95Bi0.05CuO4+delta with various values of delta b y the KMnO4 oxidation method. The largest value of delta approximate t o 0.136 is about twice as large as that obtained by annealing under hi gh pressures of oxygen, delta approximate to 0.056. A structural phase transition from the orthorhombic to the tetragonal phase with the inc rease of delta is observed at delta = 0.035-0.04. For delta greater th an or similar to 0.08, another orthorhombic phase with large orthorhom bic distortion appears and forms a mixture with the tetragonal phase. Superconductivity appears in the range of delta greater than or simila r to 0.03. In the mixture range of delta greater than or similar to 0. 08, however, the orthorhombic phase may exhibit no superconductivity d ue to the overdoping of hole carriers into the CuO2 plane. The maximum T-c increases up to similar to 35 K, which is about 10 K higher than that obtained by annealing under high pressures of oxygen, owing to th e larger hole concentration in the CuO2 plane.