PREPARATION, MAGNETIZATION AND ELECTRICAL-RESISTIVITY OF ELECTROCHEMICALLY OXIDIZED LA2CUO4+DELTA SINGLE-CRYSTALS

We report that oxygen can be intercalated at room temperature into single crystal La2CuO4 through slow electrochemical oxidation in aqueous base. Magnetic susceptibility chi(T) measurements indicate that homogeneous La2CuO4+delta crystals can be obtained with T(c) almost-equal-to 40 K. With increasing delta, two distinct superconducting phases are observed with T(c) almost-qual-to 32 and 40 K, respectively; the latter is lower than the maximum T(c) almost-equal-to 45 K of the corresponding polycrystalline samples, whereas the former is very similar. The resistivity anisotropy rho(c)/rho(ab) increases from approximately 100 at 290 K to approximately 300 at 50 K. The susceptibility anisotropy, chi(c)-chi(ab), is significantly larger than in the La2CuO4 parent crystals. The magnetically determined critical current density J(c)(H) of a La2CuO4+delta crystal with T(c)=40 K decreases exponentially with magnetic field H, with J(c)(0) approximately 5 x 10(4) and 9 X 10(4) A/cm2 for H\\c and H\\ab, respectively.