Structural and superconducting properties of La2CuO4+δ chemically oxidized by NaClO

Abstract A series of La 2 CuO 4+ δ samples chemically oxidized in NaClO aqueous solution at room temperature with different oxidation time of 2–120 h have been prepared. The X-ray powder diffraction analyses indicate that all the oxidized samples are orthorhombic and single phase, and show an enhanced orthorhombic distortion with the oxidation time, compared with that of the as-prepared sample. The magnetic susceptibility measurements indicate that all the oxidized samples are bulk superconductors with an onset transition temperature at 45 K. The excess oxygen contents of the oxidized samples determined by iodometric titration increase with the oxidation time, which versus the oxidation time obeys the law of the second order exponential decay. The grain size observed by scanning electron microscopy has no obvious changes for the sample before and after oxidation. All the results indicate that NaClO is indeed an efficient oxidizing agent for La 2 CuO 4 .