ROOM-TEMPERATURE OXIDATION OF LA2-XSRXCUO4

A series of oxidized La2-xSrxCuO4+y (0.05 less than or equal to x less than or equal to 0.3) compounds has been prepared by treating the starting materials with a solution of Br-2 in NaOH at room temperature. The structural modifications due to the oxidation of the materials have been studied by X-ray diffraction. Some of the observed changes are: (i) a large increase in the long parameter of the unit cell for samples with Sr content 0.05 less than or equal to x less than or equal to 0.15 and (ii) a slight decrease in a along the whole range of x. Interesting features have been observed regarding the critical temperatures of these materials: transition temperatures are higher for those containing lower Sr amounts (some of them were even nonsuperconducting before the oxidation treatment) in contrast to materials with x > 0.15, whose T-c's do not change very much. The influence of both oxygen and strontium contents on the structural modifications and the superconducting properties of the oxidized materials will be discussed.