Nonlinear electrodynamic properties in granular superconductors are studied
for the case of yttrium ceramic in a nonsteady-state magnetic field and in
the current state. A substantial increase in the amplitude of their even h
armonics is observed. It is shown that the nonlinear properties are determi
ned by an ensemble of vortices in the surface layer of the superconductor a
nd depend on external influences. (C) 1999 American Institute of Physics.