A new concept of polarization reversal and domain dynamics in modified ferr
oelectrics is presented. Accordingly, clusters with a reversed polarization
within ferroelectric domains are nucleated under applied field in the vici
nity of random fields around quenched defects. The random fields significan
tly lower the activation barrier required for nucleation, thus controlling
the kinetics of polarization reversal and domain dynamics. In this model, p
olarization switching occurs by the breakdown of ferroelectric long-range o
rder, through a polar cluster state. (C) 2001 American Institute of Physics
. [S0021-8979(01)00601-6].