133 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
Structural phase transitions and their influence on Cu+ mobility in superionic ferroelastic Cu6PS5I single crystals
The structural origin of Cu+ ions conductivity in Cu6PS5I single crystals is
described in terms of structural phase transitions studied by X-ray
diffraction, polarizing microscope and calorimetric measurements. Below the
phase transition at Tc=(144-169) K Cu6PS5I belongs to monoclinic, ferroelastic
phase, space group Cc. Above Tc crystal changes the symmetry to cubic
superstructure, space group F-43c (a=19.528); finally at 274K disordering of
the Cu+ ions increases the symmetry to F-43m, (a=9.794). The phase transition
at 274K coincides well with a strong anomaly in electrical conductivity
observed in the Arrhenius plot. Diffusion paths for Cu+ ions are evidenced by
means of the atomic displacement factors and split model. Influence of the
copper stechiometry on the Tc is also discussed.Comment: conference pape
Transparenz und Evaluierbarkeit des erziehungswissenschaftlichen Publikationsaufkommens. Eine anwendungsorientierte Studie
Der Beitrag stellt Ziele und erste Ergebnisse des DFG-Projekts "Innovative bibliometrische Verfahren zur kontinuierlichen Beobachtung der sozialwissenschaftlichen Forschungsproduktion" vor. Eine Analyse des Publikationsverhaltens von Erziehungswissenschaftlern zeigt die große Bedeutung des Publikationstyps Sammelwerksbeitrag und der Publikationssprache Deutsch, aber auch eine ausgeprägte Heterogenität in der Publikationspraxis von erziehungswissenschaftlichen Institutionen. Skizziert wird schließlich der Vorschlag für einen neuen, dieser Publikationspraxis angemessenen, bibliometrischen Indikator. (DIPF/Autor
Easy collective polarization switching in ferroelectrics
The actual mechanism of polarization switching in ferroelectrics remains a
puzzle for many decades, since the usually estimated barrier for nucleation and
growth is insurmountable ("paradox of the coercive field"). To analyze the
mechanisms of the nucleation we consider the exactly solvable case of a
ferroelectric film with a "dead" layer at the interface with electrodes. The
classical nucleation is easier in this case but still impossible, since the
calculated barrier is huge. We have found that the {\em interaction} between
the nuclei is, however, long range, hence one has to study an {\em ensemble} of
the nuclei. We show that there are the ensembles of small (embryonic) nuclei
that grow {\em without the barrier}. We submit that the interaction between
nuclei is the key point for solving the paradox.Comment: 5 pages, REVTeX 3.1 with one eps-figure. Corrected discussion of
single stripe and cylindrical nuclei, and their interaction. The estimate for
equilibrium density of embryonic nuclei is added. To appear in Phys. Rev.
Letter
Folding catastrophes due to viscosity in multiferroic domains : implications for room-temperature multiferroic switching
Unusual domains with curved walls and failure to satisfy the Landau–Lifshitz-Kittel Law are modeled as folding catastrophes (saddle-node bifurcations). This description of ballistic motion in a viscous medium is based upon early work by Dawber et al 2003 Appl. Phys. Lett . 82 436. It suggests that ferroelectric films can exhibit folds or vortex patterns but not both.Publisher PDFPeer reviewe
Abrupt appearance of the domain pattern and fatigue of thin ferroelectric films
We study the domain structure in ferroelectric thin films with a `passive'
layer (material with damaged ferroelectric properties) at the interface between
the film and electrodes within a continuous medium approximation. An abrupt
transition from a monodomain to a polydomain state has been found with the
increase of the `passive' layer thickness . The domain width changes very
quickly at the transition (exponentially with ). We have estimated the
dielectric response (the slope of the hysteresis loop) in the
`fatigued' multidomain state and found that it is in agreement with experiment,
assuming realistic parameters of the layer. We derive a simple universal
relation for the dielectric response, which scales as , involving only the
properties of the passive layer. This relation qualitatively reproduces the
evolution of the hysteresis loop in fatigued samples and it could be tested
with controlled experiments. It is expected that the coercive field should
increase with decreasing lateral size of the film. We believe that specific
properties of the domain structure under bias voltage in ferroelectrics with a
passive layer can resolve the long-standing `paradox of the coercive field'.Comment: 5 pages, REVTeX 3.1 with two eps-figures. Minor amendments. To appear
in Phys. Rev. Letter
Use of small specimen creep data in component life management: a review
Small specimen creep testing techniques are novel mechanical test techniques that have been developed over the past 25 years. They mainly include the sub-size uniaxial test, the small punch creep test, the impression creep test, the small ring creep test and the two-bar creep test. This paper outlines the current methods in practice for data interpretation as well as the state-of-the-art procedures for conducting the tests. Case studies for the use of impression creep testing and material strength ranking of creep resistant steels are reviewed along with the requirement for the standardisation of the impression creep test method. A database of small specimen creep testing is required to prove the validity of the tests
Modeling of dielectric hysteresis loops in ferroelectric semiconductors with charged defects
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.Comment: 21 pages, 10 figures, sent to Journal of Physics: Condensed Matte
Risks to carbon storage from land-use change revealed by peat thickness maps of Peru
This work was funded by NERC (grant ref. NE/R000751/1) to I.T.L., A.H., K.H.R., E.T.A.M., C.M.A., T.R.B., G.D. and E.C.D.G.; Leverhulme Trust (grant ref. RPG-2018-306) to K.H.R., L.E.S.C. and C.E.W.; Gordon and Betty Moore Foundation (grant no. 5439, MonANPeru network) to T.R.B., E.N.H.C. and G.F.; Wildlife Conservation Society to E.N.H.C.; Concytec/British Council/Embajada Británica Lima/Newton Fund (grant ref. 220–2018) to E.N.H.C. and J.D.; Concytec/NERC/Embajada Británica Lima/Newton Fund (grant ref. 001–2019) to E.N.H.C. and N.D.; the governments of the United States (grant no. MTO-069018) and Norway (grant agreement no. QZA-12/0882) to K.H.; and NERC Knowledge Exchange Fellowship (grant ref no. NE/V018760/1) to E.N.H.C.Tropical peatlands are among the most carbon-dense ecosystems but land-use change has led to the loss of large peatland areas, associated with substantial greenhouse gas emissions. To design effective conservation and restoration policies, maps of the location and carbon storage of tropical peatlands are vital. This is especially so in countries such as Peru where the distribution of its large, hydrologically intact peatlands is poorly known. Here field and remote sensing data support the model development of peatland extent and thickness for lowland Peruvian Amazonia. We estimate a peatland area of 62,714 km2 (5th and 95th confidence interval percentiles of 58,325 and 67,102 km2, respectively) and carbon stock of 5.4 (2.6–10.6) PgC, a value approaching the entire above-ground carbon stock of Peru but contained within just 5% of its land area. Combining the map of peatland extent with national land-cover data we reveal small but growing areas of deforestation and associated CO2 emissions from peat decomposition due to conversion to mining, urban areas and agriculture. The emissions from peatland areas classified as forest in 2000 represent 1–4% of Peruvian CO2 forest emissions between 2000 and 2016. We suggest that bespoke monitoring, protection and sustainable management of tropical peatlands are required to avoid further degradation and CO2 emissions.PostprintPeer reviewe
Qualidade do aço inoxidável martensítico do tipo AISI-420 utilizado na confecção de ferramentas cirúrgicas
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