CRITICAL-CURRENT DENSITY AND PERCOLATION IN YBACUO CERAMIC

Theoretical and experimental investigations of supercurrent percolation 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 density 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 calculated 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 the percolation threshold is close to value of 0.33 predicted by theory.