  We have proposed the phenomenological description of dielectric hysteresis
loops in ferroelectric semiconductors with charged defects and prevailing
extrinsic conductivity. Exactly we have modified Landau-Ginsburg approach and
shown that the macroscopic state of the aforementioned inhomogeneous system can
be described by three coupled equations for three order parameters. Both the
experimentally observed coercive field values well below the thermodynamic one
and the various hysteresis loop deformations (constricted and double loops)
have been obtained in the framework of our model. The obtained results
quantitatively explain the ferroelectric switching in such ferroelectric
materials as thick PZT films.
