FLUX-CREEP ACTIVATION-ENERGIES AT THE GRAIN-BOUNDARIES OF Y-BA-CU-O SUPERCONDUCTORS IN THE CHARACTERISTIC FREQUENCY BAND

Measurements on the temperature and frequency dependence of the comple x ac susceptibility of sintered Y1.01Ba1.95Cu2.97Ox are reported. The data are used to obtain the flux-creep activation energies at the grai n boundaries in the characteristic frequency band. The found nonlinear frequency dependence of these energies can be approximated differentl y in the low, characteristic, and high frequency bands. The relaxation frequency of thermal fluctuation of the vortex lattice (2piGAMMA appr oximately 3 x 10(4) Hz) and the surface current density (J(S) = 0-10 A /cm2) have been estimated.