THE PINNING OF LARGE Y2BACUO5 PRECIPITATES IN YBA2CU37-DELTA FILMS

Y2BaCuO5 is a good substance as pinning centers. The magnetic field an d temperature dependence of the pinning potential U(B,T) under the per pendicular field to c-axis was obtained as U(B,T) = U-0(1-T/T-c)(3/2)/ B-1/2 in c-axis oriented YBa2Cu3O7-delta films with high density of Y2 BaCuO5 precipitates. A straightforward consideration leads to U(B,T) p roportional to (B-c(2)/2 mu(0))alpha(f)(2) xi l/alpha(f) for a large p inning center, where alpha(f)(2) xi is the effective pinning volume an d l/a(f) is the effective number of pinned flux lines per the cross se ction of precipitates which faces against the flux motion. The magneti c field and temperature dependence of the above expression is coincide nt with our experimental results.