PERCOLATIVE CURRENT FLOW IN HIGH-J(C), POLYCRYSTALLINE HIGH-T-C SUPERCONDUCTORS

In this article, experiments designed to ascertain the percolative nat ure of current flow in high critical-current density (J(c)) polycrysta lline superconductors are reviewed. A direct correlation between the g rain-orientation texture with current transport in high-J(c) TlB2Ca2Cu 3Ox thick films and Bi2Sr2Ca2Cu3Ox powder-in-tube tapes is obtained. M agnetooptical visualization of the current flow in the same regions co nfirms the percolative nature of current flow. Furthermore, numerical modeling of the current flow based on the observed grain boundary char acter distribution and the effects of the grain boundary misorientatio n angle on J(c) was found to predict the percolative nature of current flow. These studies indicate that in order to increase the J(c) furth er, increased fractions of small-angle boundaries are required and, he nce, provide a research direction for the next generation of high-temp erature superconducting wire.