Flux pinning and irreversibility lines of new oxycarbonate superconductors (Cu/sub 0.5/C/sub 0.5/)Ba/sub 2/Ca/sub n-1/Cu/sub n/O/sub 2n+3/(n=3,4) and (Cu/sub 0.5/C/sub 0.5/)/sub 2/Ba/sub 3/Ca/sub n-1/Cu/sub n/O/sub 2n+3/(n=3,4)

Abstract

We estimated critical current densities J/sub c/'s and irreversibility fields B/sub irr/'s of new oxycarbonate superconductors, (Cu/sub 0.5/C/sub 0.5/)Ba/sub 2/Ca/sub n-1/Cu/sub n/O/sub 2n+3/(n=3,4) and (Cu/sub 0.5/C/sub 0.5/)/sub 2/Ba/sub 3/Ca/sub n-1/Cu/sub n/O/sub 2n+3/(n=3,4). (Cu,C)-based oxides, especially single (Cu,C)-layer oxides, showed less excellent flux pinning properties than other high-T/sub c/ oxide superconductors at low temperatures. The slopes of irreversibility lines for the single (Cu,C)-layer oxides were steeper than those of the double (Cu,C)-layer oxides. This result can be understood by the difference of the distance between CuO/sub 2/ superconducting blocks. At 77K, B/sub irr/ of the (Cu,C)-1234 was 3.8 T which was higher than that of Hg-1223 in spite of lower T/sub c/ of (Cu, C)-1234. Neutron irradiation to (Cu,C)-1234 significantly enhanced both J/sub c/ and B/sub irr/. About 6/spl times/10/sup 5/ A/cm/sup 2/ at 77 K in 1 T was obtained after the irradiation, which was one of the highest J/sub c/ ever reported for bulk superconductors. >