Study on the structure and superconductivity of La2CuO4+delta chemically oxidized by NaClO at 50 degrees C

A series of La2CuO4+delta samples chemically oxidized at 50 degreesC with d ifferent oxidation times using NaClO as the oxidizing agent have been prepa red. All the oxidized samples are single-phase bulk superconductors with an onset transition temperature at 42-45 K measured by dc magnetic susceptibi lity. X-ray powder diffraction indicates that all the oxidized samples are orthorhombic, and show an enhanced orthorhombic distortion with the oxidati on time, compared with that of the starting material. The excess oxygen con tents of the oxidized samples determined by iodometric titration are large and increase with the oxidation time. The fit to the experimental data reve als that the excess oxygen content versus the oxidation time obeys the law of the second-order exponential decay. No obvious changes in the grains of the samples before and after oxidation have been observed by scanning elect ron microscopy.