  We have modified Landau-Khalatnikov approach and shown that the pyroelectric
response of inhomogeneous ferroelectric-semiconductor films can be described by
using six coupled equations for six order parameters: average displacement, its
mean-square fluctuation and correlation with charge defects density
fluctuations, average pyroelectric coefficient, its fluctuation and correlation
with charge defects density fluctuations. Coupled equations demonstrate the
inhomogeneous reversal of pyroelectric response in contrast to the equations of
Landau-Khalatnikov type, which describe the homogeneous reversal with the sharp
pyroelectric coefficient peak near the thermodynamic coercive field value.
Within the framework of our model pyroelectric hysteresis loop becomes much
smoother, thinner and lower as well as pyroelectric coefficient peaks near the
coercive field completely disappear under the increase of disordering caused by
defects. This effect is similar to the well-known "square to slim transition"
of the ferroelectric hysteresis loops in relaxor ferroelectrics. Also the
increase of defect concentration leads to the drastic decrease of the coercive
field typical for disordered ferroelectrics. Usually pyroelectric hysteresis
loops of doped and inhomogeneous ferroelectrics have typical smooth shape
without any pyroelectric coefficient peaks and coercive field values much lower
than the thermodynamic one. Therefore our approach qualitatively explains
available experimental results. Rather well quantitative agreement between our
modelling and typical Pb(Zr,Ti)O3-film pyroelectric and ferroelectric loops has
been obtained.
