351 research outputs found
Domain walls of ferroelectric BaTiO3 within the Ginzburg-Landau-Devonshire phenomenological model
Mechanically compatible and electrically neutral domain walls in tetragonal,
orthorhombic and rhombohedral ferroelectric phases of BaTiO3 are systematically
investigated in the framework of the phenomenological
Ginzburg-Landau-Devonshire (GLD) model with parameters of Ref. [Hlinka and
Marton, Phys. Rev. 74, 104104 (2006)]. Polarization and strain profiles within
domain walls are calculated numerically and within an approximation leading to
the quasi-one-dimensional analytic solutions applied previously to the
ferroelectric walls of the tetragonal phase [W. Cao and L.E. Cross, Phys. Rev.
44, 5 (1991)]. Domain wall thicknesses and energy densities are estimated for
all mechanically compatible and electrically neutral domain wall species in the
entire temperature range of ferroelectric phases. The model suggests that the
lowest energy walls in the orthorhombic phase of BaTiO3 are the 90-degree and
60-degree walls. In the rhombohedral phase, the lowest energy walls are the
71-degree and 109-degree walls. All these ferroelastic walls have thickness
below 1 nm except for the 90-degree wall in the tetragonal phase and the
60-degree S-wall in the orthorhombic phase, for which the larger thickness of
the order of 5 nm was found. The antiparallel walls of the rhombohedral phase
have largest energy and thus they are unlikely to occur. The calculation
indicates that the lowest energy structure of the 109-degree wall and few other
domain walls in the orthorhombic and rhombohedral phases resemble Bloch-like
walls known from magnetism.Comment: 12 pages, 9 figure
Comment on ``Elastic Stabilization of a Single-Domain Ferroelectric State in Nanoscale Capacitors and Tunnel Junctions" [N.A. Pertsev and H. Kohlstedt, Phys. Rev. Lett. 98, 257603 (2007).]
In a recent Letter [N.A. Pertsev and H. Kohlstedt, Phys. Rev. Lett. 98,
257603 (2007)] the authors claim that "even nanoscale capacitors and tunnel
junctions may have out of plane polarization sufficient for memory
applications." Here we show in an elementary way that this conclusion is not
substantiated by their calculations and that they should have come to the
opposite conclusion within their approximations.Comment: 2 pages, no figure
Correlation Between Structure And C-Afm Contrast Of 180-Degree Domain Walls In Rhombohedral Bati03
Using Landau-Ginzburg-Devonshire theory we describe 180-degree domain wall
structure, intrinsic energy and carrier accumulation in rhombohedral phase of
BaTiO3 as a function of the wall orientation and flexoelectric coupling
strength. Two types of domain wall structures (phases of the wall) exist
depending on the wall orientation. The low-energy 'achiral' phase occurs in the
vicinity of the {110} wall orientation and has odd polarization profile
invariant with respect to inversion about the wall center. The second 'chiral'
phase occurs around {211} wall orientations and corresponds to mixed parity
domain walls that may be of left-handed or right-handed chirality. The
transformation between the phases is abrupt, accompanied with 20-30% change of
the domain wall thickness and can happen at fixed wall orientation with
temperature change. We suggest that the phase transition may be detected
through domain wall thickness change or by c-AFM. The structure of the domain
wall is correlated to its conductivity through polarization component normal to
the domain wall, which causes free carriers accumulation. Depending on the
temperature and flexoelectric coupling strength relative conductivity of the
wall becomes at least one order of magnitude higher than in the single-domain
region, creating c-AFM contrast enhancement pronounced and detectable.Comment: 31 pages, 10 figures, Supplementary material
Landau-Ginzburg-Devonshire theory for electromechanical hysteresis loop formation in piezoresponse force microscopy of thin films
Electromechanical hysteresis loop formation in piezoresponse force microscopy
of thin ferroelectric films is studied with special emphasis on the effects of
tip size and film thickness, as well as dependence on the tip voltage
frequency. Here, we use a combination of Landau-Ginzburg-Devonshire (LGD)
theory for the description of the local polarization reversal with decoupling
approximation for the calculation of the local piezoresponse loops shape,
coercive voltages and amplitude. LGD approach enables addressing both
thermodynamics and kinetics of hysteresis loop formation. In contrast to the
"rigid" ferroelectric approximation, this approach allows for the piezoelectric
tensor components dependence on the ferroelectric polarization and dielectric
permittivity. This model rationalizes the non-classical shape of the dynamic
piezoelectric force microscopy (PFM) loops.Comment: 23 pages, 5 figures, 1 appendix,to be submitted to J. Appl. Phy
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.
Magnetic Moment Softening and Domain Wall Resistance in Ni Nanowires
Magnetic moments in atomic scale domain walls formed in nanoconstrictions and
nanowires are softened which affects dramatically the domain wall resistance.
We perform ab initio calculations of the electronic structure and conductance
of atomic-size Ni nanowires with domain walls only a few atomic lattice
constants wide. We show that the hybridization between noncollinear spin states
leads to a reduction of the magnetic moments in the domain wall. This magnetic
moment softening strongly enhances the domain wall resistance due to scattering
produced by the local perturbation of the electronic potential.Comment: 4 pages, 5 figure
The Interaction of an 180 degree Ferroelectric Domain Wall with a Biased Scanning Probe Microscopy Tip: Effective Wall Geometry and Thermodynamics in Ginzburg-Landau-Devonshire Theory
The interaction of ferroelectric 180 degree domain wall with a strongly
inhomogeneous electric field of biased Scanning Probe Microscope tip is
analyzed within continuous Landau-Ginzburg-Devonshire theory. Equilibrium shape
of the initially flat domain wall boundary bends, attracts or repulses from the
probe apex, depending on the sign and value of the applied bias. For large
tip-wall separations, the probe-induced domain nucleation is possible. The
approximate analytical expressions for the polarization distribution are
derived using direct variational method. The expressions provide insight how
the equilibrium polarization distribution depends on the wall finite-width,
correlation and depolarization effects, electrostatic potential distribution of
the probe and ferroelectric material parameters.Comment: 37 pages, 9 figures, 4 Appendices, to be submitted to Phys. Rev.
ΠΠ°ΡΠ°ΠΌΠ΅ΡΡΡ ΠΏΠ΅ΡΠΈΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΊΡΠΎΠ²ΠΈ ΠΊΠ°ΠΊ ΠΌΠ°ΡΠΊΠ΅ΡΡ Π½Π΅ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π°Π΄Π°ΠΏΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ ΠΎΡΠ²Π΅ΡΠ° ΠΏΡΠΈ ΠΎΡΡΡΡΡ ΠΈΠ½ΡΠ΅ΠΊΡΠΈΠΎΠ½Π½ΡΡ Π·Π°Π±ΠΎΠ»Π΅Π²Π°Π½ΠΈΡΡ Ρ ΡΠΈΠ½Π΄ΡΠΎΠΌΠΎΠΌ ΡΠΎΠ½Π·ΠΈΠ»Π»ΠΈΡΠ°
Evaluation of nonspecific adaptive response of the body in children with acute infectious diseases associated with tonsillitis syndrome was the aim of this research. This prospective study included clinical, anamnestic and laboratory examination of children with acute infectious diseases with tonsillitis syndrome. A systemic multiple factor analysis was conducted (significance level Ρ<0.05). The evaluation of peripheral blood parameters (specific gravity of lymphocytes and indices of reactive protective potential (RPP) - specific immune lymphocytic-monocytic parameter (SILMP) and coefficient of phagocytic defense (CPD)) gives the possibility to determine the condition of nonspecific adaptation in children with acute infectious diseases associated with tonsillitis syndrome. Children with tonsillitis syndrome show significant increase of integral RPP parameters, i.e. decrease of RPP, which is more pronounced on discharge (on admission - in 57% of children, on discharge - in 87%). The most unfavourable initial nonspecific adaptative body response (NABR) (according to the percentage of lymphocytes) is the reaction of increased activation, as it is associated with the transition to the overactivation by the time of discharge (37% of children). Systemic multiple factor analysis determined which peripheral blood parameters have more influence on childrenβs adaptation during the course of infectious disease: RPP indices showed high influence coefficients in all diseases (CPD was the highest in bacterial infection - Π i 198.3; SILMP was the highest in viral infection - Π i 147.81; in mixed infection CPD and SILMP were roughly the same - Π i β 107.25 and Π i - 78.11, respectively), which proves the feasibility of RPP evaluation for prognostic purposes in the treatment of this category of patients.Π¦Π΅Π»ΡΡ Π½Π°ΡΡΠΎΡΡΠ΅Π³ΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΡΠ²ΠΈΠ»Π°ΡΡ ΠΎΡΠ΅Π½ΠΊΠ° Π½Π΅ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠΉ Π°Π΄Π°ΠΏΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΠ΅Π°ΠΊΡΠΈΠΈ ΠΎΡΠ³Π°Π½ΠΈΠ·ΠΌΠ° Ρ Π΄Π΅ΡΠ΅ΠΉ Ρ ΠΎΡΡΡΡΠΌΠΈ ΠΈΠ½ΡΠ΅ΠΊΡΠΈΠΎΠ½Π½ΡΠΌΠΈ Π·Π°Π±ΠΎΠ»Π΅Π²Π°Π½ΠΈΡΠΌΠΈ, Π°ΡΡΠΎΡΠΈΠΈΡΠΎΠ²Π°Π½Π½ΡΠΌΠΈ Ρ ΡΠΈΠ½Π΄ΡΠΎΠΌΠΎΠΌ ΡΠΎΠ½Π·ΠΈΠ»Π»ΠΈΡΠ°. ΠΠ°Π½Π½ΠΎΠ΅ ΠΏΡΠΎΡΠΏΠ΅ΠΊΡΠΈΠ²Π½ΠΎΠ΅ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ Π²ΠΊΠ»ΡΡΠ°Π»ΠΎ ΠΊΠ»ΠΈΠ½ΠΈΠΊΠΎ-Π°Π½Π°ΠΌΠ½Π΅ΡΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΠΈ Π»Π°Π±ΠΎΡΠ°ΡΠΎΡΠ½ΠΎΠ΅ ΠΎΠ±ΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ Π΄Π΅ΡΠ΅ΠΉ Ρ ΠΎΡΡΡΡΠΌΠΈ ΠΈΠ½ΡΠ΅ΠΊΡΠΈΠΎΠ½Π½ΡΠΌΠΈ Π·Π°Π±ΠΎΠ»Π΅Π²Π°Π½ΠΈΡΠΌΠΈ Ρ ΡΠΈΠ½Π΄ΡΠΎΠΌΠΎΠΌ ΡΠΎΠ½Π·ΠΈΠ»Π»ΠΈΡΠ°. ΠΡΠΎΠ²Π΅Π΄Π΅Π½ ΡΠΈΡΡΠ΅ΠΌΠ½ΡΠΉ ΠΌΠ½ΠΎΠ³ΠΎΡΠ°ΠΊΡΠΎΡΠ½ΡΠΉ Π°Π½Π°Π»ΠΈΠ· (ΡΡΠΎΠ²Π΅Π½Ρ Π·Π½Π°ΡΠΈΠΌΠΎΡΡΠΈ Ρ<0,05). ΠΡΠ΅Π½ΠΊΠ° ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»Π΅ΠΉ ΠΏΠ΅ΡΠΈΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΊΡΠΎΠ²ΠΈ (ΡΠ΄Π΅Π»ΡΠ½ΠΎΠ³ΠΎ Π²Π΅ΡΠ° Π»ΠΈΠΌΡΠΎΡΠΈΡΠΎΠ² ΠΈ ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»Π΅ΠΉ ΡΠ΅Π°ΠΊΡΠΈΠ²Π½ΠΎ-ΠΏΡΠΎΡΠ΅ΠΊΡΠΈΠ²Π½ΡΠΉ ΠΏΠΎΡΠ΅Π½ΡΠΈΠ°Π» (Π ΠΠ) - ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΈΠΌΠΌΡΠ½Π½ΠΎΠ³ΠΎ Π»ΠΈΠΌΡΠΎΡΠΈΡΠ°ΡΠ½ΠΎ-ΠΌΠΎΠ½ΠΎΡΠΈΡΠ°ΡΠ½ΠΎΠ³ΠΎ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΠ° (ΠΠΠΠ) ΠΈ ΠΊΠΎΡΡΡΠΈΡΠΈΠ΅Π½ΡΠ° ΡΠ°Π³ΠΎΡΠΈΡΠ°ΡΠ½ΠΎΠΉ Π·Π°ΡΠΈΡΡ (ΠΠ€Π) Π΄Π°Π΅Ρ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎΡΡΡ ΠΎΠΏΡΠ΅Π΄Π΅Π»ΠΈΡΡ ΡΠΎΡΡΠΎΡΠ½ΠΈΠ΅ Π½Π΅ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠΉ Π°Π΄Π°ΠΏΡΠ°ΡΠΈΠΈ Ρ Π΄Π΅ΡΠ΅ΠΉ Ρ ΠΎΡΡΡΡΠΌΠΈ ΠΈΠ½ΡΠ΅ΠΊΡΠΈΠΎΠ½Π½ΡΠΌΠΈ Π·Π°Π±ΠΎΠ»Π΅Π²Π°Π½ΠΈΡΠΌΠΈ, Π°ΡΡΠΎΡΠΈΠΈΡΠΎΠ²Π°Π½Π½ΡΠΌΠΈ Ρ ΡΠΈΠ½Π΄ΡΠΎΠΌΠΎΠΌ ΡΠΎΠ½Π·ΠΈΠ»Π»ΠΈΡΠ°. Π£ Π΄Π΅ΡΠ΅ΠΉ Ρ ΡΠΈΠ½Π΄ΡΠΎΠΌΠΎΠΌ ΡΠΎΠ½Π·ΠΈΠ»Π»ΠΈΡΠ° ΠΎΡΠΌΠ΅ΡΠ°Π΅ΡΡΡ Π΄ΠΎΡΡΠΎΠ²Π΅ΡΠ½ΠΎΠ΅ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΠ΅ ΠΈΠ½ΡΠ΅Π³ΡΠ°Π»ΡΠ½ΡΡ
ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»Π΅ΠΉ Π ΠΠ, Ρ. Π΅. ΡΠ½ΠΈΠΆΠ΅Π½ΠΈΠ΅ Π ΠΠ, ΠΊΠΎΡΠΎΡΠΎΠ΅ Π±ΠΎΠ»Π΅Π΅ Π²ΡΡΠ°ΠΆΠ΅Π½ΠΎ ΠΏΡΠΈ Π²ΡΠΏΠΈΡΠΊΠ΅ (ΠΏΡΠΈ ΠΏΠΎΡΡΡΠΏΠ»Π΅Π½ΠΈΠΈ - Ρ 57% Π΄Π΅ΡΠ΅ΠΉ, ΠΏΡΠΈ Π²ΡΠΏΠΈΡΠΊΠ΅ - Ρ 87%). ΠΠ°ΠΈΠ±ΠΎΠ»Π΅Π΅ Π½Π΅Π±Π»Π°Π³ΠΎΠΏΡΠΈΡΡΠ½ΠΎΠΉ ΠΈΡΡ
ΠΎΠ΄Π½ΠΎΠΉ Π½Π΅ΡΠΏΠ΅ΡΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠΉ Π°Π΄Π°ΠΏΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΡΠ΅Π°ΠΊΡΠΈΠ΅ΠΉ ΠΎΡΠ³Π°Π½ΠΈΠ·ΠΌΠ° (ΠΏΠΎ ΠΏΡΠΎΡΠ΅Π½ΡΡ Π»ΠΈΠΌΡΠΎΡΠΈΡΠΎΠ²) ΡΠ²Π»ΡΠ΅ΡΡΡ ΡΠ΅Π°ΠΊΡΠΈΡ ΠΏΠΎΠ²ΡΡΠ΅Π½Π½ΠΎΠΉ Π°ΠΊΡΠΈΠ²Π°ΡΠΈΠΈ, ΡΠ°ΠΊ ΠΊΠ°ΠΊ ΠΎΠ½Π° ΡΠ²ΡΠ·Π°Π½Π° Ρ ΠΏΠ΅ΡΠ΅Ρ
ΠΎΠ΄ΠΎΠΌ ΠΊ Π³ΠΈΠΏΠ΅ΡΠ°ΠΊΡΠΈΠ²Π°ΡΠΈΠΈ ΠΊ ΠΌΠΎΠΌΠ΅Π½ΡΡ Π²ΡΠΏΠΈΡΠΊΠΈ (37% Π΄Π΅ΡΠ΅ΠΉ). Π‘ΠΈΡΡΠ΅ΠΌΠ½ΡΠΉ ΠΌΠ½ΠΎΠ³ΠΎΡΠ°ΠΊΡΠΎΡΠ½ΡΠΉ Π°Π½Π°Π»ΠΈΠ· ΠΎΠΏΡΠ΅Π΄Π΅Π»ΠΈΠ», ΠΊΠ°ΠΊΠΈΠ΅ ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»ΠΈ ΠΏΠ΅ΡΠΈΡΠ΅ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΊΡΠΎΠ²ΠΈ ΠΎΠΊΠ°Π·ΡΠ²Π°ΡΡ Π±ΠΎΠ»ΡΡΠ΅Π΅ Π²Π»ΠΈΡΠ½ΠΈΠ΅ Π½Π° Π°Π΄Π°ΠΏΡΠ°ΡΠΈΡ Π΄Π΅ΡΠ΅ΠΉ Π² ΡΠ΅ΡΠ΅Π½ΠΈΠ΅ ΠΈΠ½ΡΠ΅ΠΊΡΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ Π·Π°Π±ΠΎΠ»Π΅Π²Π°Π½ΠΈΡ: ΠΏΠΎΠΊΠ°Π·Π°ΡΠ΅Π»ΠΈ Π ΠΠ ΠΏΠΎΠΊΠ°Π·Π°Π»ΠΈ Π²ΡΡΠΎΠΊΠΈΠ΅ ΠΊΠΎΡΡΡΠΈΡΠΈΠ΅Π½ΡΡ Π²Π»ΠΈΡΠ½ΠΈΡ ΠΏΡΠΈ Π²ΡΠ΅Ρ
Π·Π°Π±ΠΎΠ»Π΅Π²Π°Π½ΠΈΡΡ
, ΡΡΠΎ Π΄ΠΎΠΊΠ°Π·ΡΠ²Π°Π΅Ρ ΡΠ΅Π»Π΅ΡΠΎΠΎΠ±ΡΠ°Π·Π½ΠΎΡΡΡ ΠΎΡΠ΅Π½ΠΊΠΈ Π ΠΠ Π² ΠΏΡΠΎΠ³Π½ΠΎΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ΅Π»ΡΡ
ΠΏΡΠΈ Π»Π΅ΡΠ΅Π½ΠΈΠΈ Π΄Π°Π½Π½ΠΎΠΉ ΠΊΠ°ΡΠ΅Π³ΠΎΡΠΈΠΈ Π±ΠΎΠ»ΡΠ½ΡΡ
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