Composition of Superconducting La2 CuO(4+delta): A Superconductor Doped by Excess Oxygen Defects.

摘要

We have studied mixed-phase samples of bulk La(sub z)CuO4 using neutron powder diffraction, thermogravimetric analysis and resistivity measurements. Samples fired at 950C and slowly cooled form in the K2 NiF4 structure with CuO impurities for z2. Neither La-vacancies nor stacking defects were found. The bulk resistivity of the samples show semiconducting behavior which is shorted at 38K by small amounts of superconducting material. The superconductivity is due to the presence of an oxygen-rich phase with stoichiometry La2 CuO4.08. The occurrence of superconductivity in pure La2 CuO4.08 with the same Tc as observed in the doped La1.85Sr 0.15CuO4 indicates that the excess oxygen provides the same level of doping as metal-ion substitution. 19 refs., 8 figs., 1 tab.