145 research outputs found
Pyroelectric response of ferroelectric nanoparticles: size effect and electric energy harvesting
The size effect on pyroelectric response of ferroelectric nanowires and
nanotubes is analyzed. The pyroelectric coefficient strongly increases with the
wire radius decrease and diverges at critical radius Rcr corresponding to the
size-driven transition into paraelectric phase. Size-driven enhancement of
pyroelectric coupling leads to the giant pyroelectric current and voltage
generation by the polarized ferroelectric nanoparticles in response to the
temperature fluctuation. The maximum efficiency of the pyroelectric energy
harvesting and bolometric detection is derived, and is shown to approach the
Carnot limit for low temperatures.Comment: 17 pages, 4 figures, 1 Appendi
Mesoscopic mechanism of the domain wall interaction with elastic defects in ferroelectrics
The role of elastic defects on the kinetics of 180-degree uncharged
ferroelectric domain wall motion is explored using continuum time-dependent LGD
equation with elastic dipole coupling. In one dimensional case, ripples, steps
and oscillations of the domain wall velocity appear due to the wall-defect
interactions. While the defects do not affect the limiting-wall velocity vs.
field dependence, they result in the minimal threshold field required to
activate the wall motions. The analytical expressions for the threshold field
are derived and the latter is shown to be much smaller than the thermodynamic
coercive field. The threshold field is linearly proportional to the
concentration of defects and non-monotonically depends on the average distance
between them. The obtained results provide the insight into the mesoscopic
mechanism of the domain wall pinning by elastic defects in ferroelectrics.Comment: 18 pages, 6 figures, 1 appendi
Reliability of AC thick-film electroluminescent lamps
The reliability of AC thick-film EL devices has been studied. The AC thickfilm
EL devices were fabricated by Novatech Inc. using the industrial print screen
technology. The analysis of reasons for failure has been proposed. The dependence of EL
lamp parameters on physical properties of the device EL layers was found. Our analysis
of the breakdown spot showed that improvement of reliability can be reached using the
additional dielectric layer between the phosphor layer and transparent electrode, high
concentration of phosphor powder 70 % and binder 30 %, balanced resistance between
the electric circuit and EL lamp. The thickness of the phosphor layer was equal to H =
(1 + √3/2)D (hexagonal packing), where D is the mean diameter of phosphor particles.
The reliability dependence of EL lamp on a water adsorption property of packaging
material was revealed
Endocrine Disruptors and Leydig Cell Function
During the past decades, a large body of information concerning the effects of endocrine disrupting compounds (EDCs) on animals and humans has been accumulated. EDCs are of synthetic or natural origin and certain groups are known to disrupt the action of androgens and to impair the development of the male reproductive tract and external genitalia. The present overview describes the effects of the different classes of EDCs, such as pesticides, phthalates, dioxins, and phytoestrogens, including newly synthesized resveratrol analogs on steroidogenesis in Leydig cells. The potential impact of these compounds on androgen production by Leydig cells during fetal development and in the adult age is discussed. In addition, the possible role of EDCs in connection with the increasing frequency of abnormalities in reproductive development in animals and humans is discussed
Static conductivity of charged domain wall in uniaxial ferroelectric-semiconductors
Using Landau-Ginzburg-Devonshire theory we calculated numerically the static
conductivity of both inclined and counter domain walls in the uniaxial
ferroelectrics-semiconductors of n-type. We used the effective mass
approximation for the electron and holes density of states, which is valid at
arbitrary distance from the domain wall. Due to the electrons accumulation, the
static conductivity drastically increases at the inclined head-to-head wall by
1 order of magnitude for small incline angles theta pi/40 by up 3 orders of
magnitude for the counter domain wall (theta=pi/2). Two separate regions of the
space charge accumulation exist across an inclined tail-to-tail wall: the thin
region in the immediate vicinity of the wall with accumulated mobile holes and
the much wider region with ionized donors. The conductivity across the
tail-to-tail wall is at least an order of magnitude smaller than the one of the
head-to-head wall due to the low mobility of holes, which are improper carries.
The results are in qualitative agreement with recent experimental data for
LiNbO3 doped with MgO.Comment: 20 pages, 6 figures, 1 appendi
Finite size and intrinsic field effect on the polar-active properties of the ferroelectric-semiconductor heterostructures
Using Landau-Ginzburg-Devonshire approach we calculated the equilibrium
distributions of electric field, polarization and space charge in the
ferroelectric-semiconductor heterostructures containing proper or incipient
ferroelectric thin films. The role of the polarization gradient and intrinsic
surface energy, interface dipoles and free charges on polarization dynamics are
specifically explored. The intrinsic field effects, which originated at the
ferroelectric-semiconductor interface, lead to the surface band bending and
result into the formation of depletion space-charge layer near the
semiconductor surface. During the local polarization reversal (caused by the
inhomogeneous electric field induced by the nanosized tip of the Scanning Probe
Microscope (SPM) probe) the thickness and charge of the interface layer
drastically changes, it particular the sign of the screening carriers is
determined by the polarization direction. Obtained analytical solutions could
be extended to analyze polarization-mediated electronic transport.Comment: 35 pages, 12 figures, 1 table, 2 appendices, to be submitted to Phys.
Rev.
Domain wall conduction in multiaxial ferroelectrics
The conductance of domain wall structures consisting of either stripes or
cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed.
The effects of the domain size, wall tilt and curvature, on charge
accumulation, are analyzed using the Landau-Ginsburg Devonshire (LGD) theory
for polarization combined with Poisson equation for charge distributions. Both
the classical ferroelectric parameters including expansion coefficients in
2-4-6 Landau potential and gradient terms, as well as flexoelectric coupling,
inhomogeneous elastic strains and electrostriction are included in the present
analysis. Spatial distributions of the ionized donors, free electrons and holes
were found self-consistently using the effective mass approximation for the
respective densities of states. The proximity and size effect of the electron
and donor accumulation/depletion by thin stripe domains and cylindrical
nanodomains are revealed. In contrast to thick domain stripes and thicker
cylindrical domains, in which the carrier accumulation (and so the static
conductivity) sharply increases at the domain walls only, small nanodomains of
radius less then 5-10 correlation length appeared conducting across entire
cross-section. Implications of such conductive nanosized channels may be
promising for nanoelectronics.Comment: 39 pages, 11 figures, 3 tables, 4 appendice
Thermodynamics of nanodomain formation and breakdown in Scanning Probe Microscopy: Landau-Ginzburg-Devonshire approach
Thermodynamics of tip-induced nanodomain formation in scanning probe
microscopy of ferroelectric films and crystals is studied using the
Landau-Ginzburg-Devonshire phenomenological approach. The local redistribution
of polarization induced by the biased probe apex is analyzed including the
effects of polarization gradients, field dependence of dielectric properties,
intrinsic domain wall width, and film thickness. The polarization distribution
inside subcritical nucleus of the domain preceding the nucleation event is very
smooth and localized below the probe, and the electrostatic field distribution
is dominated by the tip. In contrast, polarization distribution inside the
stable domain is rectangular-like, and the associated electrostatic fields
clearly illustrate the presence of tip-induced and depolarization field
components. The calculated coercive biases of domain formation are in a good
agreement with available experimental results for typical ferroelectric
materials. The microscopic origin of the observed domain tip elongation in the
region where the probe electric field is much smaller than the intrinsic
coercive field is the positive depolarization field in front of the moving
counter domain wall. For infinitely thin domain walls local domain breakdown
through the sample depth appears. The results obtained here are complementary
to the Landauer-Molotskii energetic approach.Comment: 35 pages, 8 figures, suplementary attached, to be submitted to Phys.
Rev.
Frequency Dependent Dynamical Electromechanical Response of Mixed Ionic-Electronic Conductors
Frequency dependent dynamic electromechanical response of the mixed
ionic-electronic conductor film to a periodic electric bias is analyzed for
different electronic and ionic boundary conditions. Dynamic effects of mobile
ions concentration (stoichiometry contribution), charge state of acceptors
(donors), electron concentration (electron-phonon coupling via the deformation
potential) and flexoelectric effect contribution are discussed. A variety of
possible nonlinear dynamic electromechanical response of MIEC films including
quasi-elliptic curves, asymmetric hysteresis-like loops with pronounced memory
window and butterfly-like curves are calculated. The electromechanical response
of ionic semiconductor is predicted to be a powerful descriptor of local
valence states, band structure and electron-phonon correlations that can be
readily measured in the nanoscale volumes and in the presence of strong
electronic conductivity.Comment: 36 pages, 10 figures, accepted to J. Appl. Phy
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