Superconductivity and flux pinning in Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7+ delta /

摘要

The substitution of Nd/sup +3/ for Ba/sup +2/ in Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7/ (Nd123ss) increases the occupation of O(5) sites. For x<0.1 there is a significant depression of T/sub c/, and for x>0.1 there is no substantial decrease in T/sub c/ within experimental error. T/sub c/ vs. x is characterized by two plateaus, analogously to T/sub c/ vs. delta in YBa/sub 2/Cu/sub 3/O/sub 7- delta / (Y123). Analysis of oxygen contents of Nd123ss suggests the analogy with Y123 is valid. The transition width and Meissner fraction for all Nd123ss samples are strongly dependent on the sintering temperatures. While T/sub c/ is not affected over the range 0>x>0.1, the oxygen atoms surrounding the substituted Ba sites are expected to locally suppress the superconducting order parameter. Hysteresis measurements exhibited a small increase in the magnetic J/sub c/, but flux creep measurements showed no apparent effects of this substitution on the flux pinning energy.