Harmonic ac susceptibilities were measured as a function of temperatur
e (T), ac field frequency (f) and amplitude (B-ac,), and de field (B-d
c,) for bulk textured YBa2Cu3O7. The higher harmonics consist mainly o
f odd ones in strong de fields (B-dc, > 50 mT) and depend on B-dc, B-a
c, and f. It is confirmed that the origin of harmonic generation for t
he textured sample is thermally activated flux diffusion over barriers
Ci which depend nonlinearly on current density (j). The high nonlinea
r flux diffusion induces a self-organized Bean critical state in which
the straight line approximation is a good description of the field pr
ofile except that the current density is j(f) instead of the critical
value j(c). Thus the frequency dependent Bean critical state accounts
for the origin of harmonic generation and explains the present and oth
er experiments well. (C) 1997 Elsevier Science B.V.