STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF La2CuO4+δ OXIDIZED BY KMnO4 UNDER HYDROTHERMAL CONDITIONS

A series of samples of La2CuO4+δ chemically oxidized in KMnO4 solution under hydro-thermal conditions have been prepared. A large orthorhombic distortion and the increased unit cell volume of the oxidized sample have been observed by means of X-ray powder diffraction, compared with that of the starting material. Selected-area electron diffraction investigations reveal that two kinds of incommensurate modulation structures exist in the oxidized samples. Magnetic susceptibility measurements indicate that the oxidized samples are multiphase with two superconducting phases, one is dominant with onset of superconducting transition temperature at 43 K or 40 K, and the other at 19 K. Up to now, a Tc of 43 K is the highest value achieved in KMnO4-treated samples. The excess oxygen content determined by iodometric titration increases with the oxidation temperature. Average grain sizes observed by scanning electron microscope have no obvious changes for the samples before and after oxidation.