328 research outputs found
Modeling of micro- and nano-scale domain recording by high-voltage atomic force microscopy in ferroelectrics-semiconductors
The equilibrium sizes of micro- and nano-domains caused by electric field of
atomic force microscope tip in ferroelectric semiconductor crystals have been
calculated. The domain was considered as a prolate semi-ellipsoid with rather
thin domain walls. For the first time we modified the Landauer model allowing
for semiconductor properties of the sample and the surface energy of the domain
butt. The free carriers inside the crystal lead to the formation of the
screening layer around the domain, which partially shields its interior from
the depolarization field. We expressed the radius and length of the domain
though the crystal material parameters (screening radius, spontaneous
polarization value, dielectric permittivity tensor) and atomic force microscope
tip characteristics (charge, radius of curvature). The obtained dependence of
domain radius via applied voltage is in a good quantitative agreement with the
ones of submicron ferroelectric domains recorded by high-voltage atomic force
and scanning probe microscopy in LiNbO3 and LiTaO3 crystals.Comment: 21 pages, 5 figure
Modelling of Pyroelectric Response in Inhomogeneous Ferroelectric-Semiconductor Films
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.Comment: 14 pages, 5 figure
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