THE SUPERCONDUCTING PROPERTIES AND X-RAY-ABSORPTION STRUCTURE DATA OFBAPB0.75BI0.25O3 AT OXYGEN DEFICIENCY

The superconducting properties of BaPb0.75Bi0.25O3-delta have been stu died through the transport measuring and x-ray absorption spectroscopy O(AS) as a function of oxygen content deficiency ( 0 less than or equ al to delta less than or equal to 0.15). We found the appearance of se miconducting behaviour rho(T) just at delta similar to 0.02. However t he superconducting transition takes place at T-c similar to 7 divided by 11K up to delta less than or equal to 0.15 according to ac suscepti bility measurements. The metal-insulator transition occurs firstly at the boundaries of the ceramic grains. The local and electronic structu res of BaPb0.75Bi0.O-25(3-delta) have been defined by XAS on L(3) Pb(B i) edges. The Pb-O octahedra does not practically change while the oxy gen leaves the Bi-O sites. The superconductivity deterioration at oxyg en deficiency is accompanied by changes in electronic structure of Bi- O complexes.