INFLUENCE OF FLUORINE ON THE PROPERTIES OF ND1.85CE0.15CUO4-DELTA N-TYPE SUPERCONDUCTOR

The fluorine-doped n-type superconductors Nd1.85Ce0.15CuO4-x-yFy (nomi nal composition) are synthesized with CuF2 as one of the reactants. Es pecially, it is found that the superconductivity of Nd1.85Ce0.15CuO4-d elta is improved with T-c(on) = 27 K, T-c(0) = 15.5 K when CuF2 is tak en as a source of atmosphere; the temperature dependence of the resist ance exhibits a metallic conducting behavior above T-c. Magnetization measurements showed 30% of superconducting phase fractions by means of SQUID magnetometry, which was a better result of superconductivity in (Nd,Ce)-Cu-O bulk samples than when prepared under ambient pressure. Compared with the cast of F undoping, F doping not only induces a tran sition from semiconductivity to metallic conductivity and decreases th e normal-state resistivity, but also increases the T-c(on) and T-c(0), and decreases the transition width Delta T-c. In particular, the supe rconductivity of the samples is sensitive to the form of the dopant so urce and sintering procedures, Especially, the Nd1.85Ce0.15CuO3.6F0.4 sintered only in air also exhibits superconductivity with T-c(on) = 19 .5 K, but does not reach zero resistance, which has not been reported before. X-ray diffraction experiments indicate that fluorine atoms do enter the superconducting phase lattice.