CRITICAL-CURRENT DENSITY AND PERCOLATION IN YBACUO CERAMIC

Theoretical and experimental investigations of supercurrent percolatio n in granular YBaCuO ceramic have been carried out. In the mean field approximation the expression for critical current density j(c) = j(c0) (p(s)-1/3) has been derived. Here j(c0) is the critical current densi ty of an infinite skeleton cluster, p(s) = k(rho)/rho(id), where k is the share of the superconducting phase, rho(id) = 6.35 g/cm3 is the ca lculated value of the maximal density. Three series of YBaCuO samples with rho in the range 3.5-5.4 g/cm3 and different values of k = 0.7, 0 .9 and 0.95 have been investigated experimentally. Linear dependences of j(c)(rho) and j(c)(p(s)) are obtained. The experimental value of th e percolation threshold is close to value of 0.33 predicted by theory.