Physical and structural origins of morphotropic phase boundaries (MPBs) in ferroics remain elusive despite decades of study. The leading competing theories employ either low-symmetry bridging phases ...or adaptive phases with nanoscale textures to describe different subsets of the macroscopic data, while the decisive atomic-scale information has so far been missing. Here we report direct atomically resolved mapping of polarization and structure order parameter fields in a Sm-doped BiFeO(3) system and their evolution as the system approaches a MPB. We further show that both the experimental phase diagram and the observed phase evolution can be explained by taking into account the flexoelectric interaction, which renders the effective domain wall energy negative, thus stabilizing modulated phases in the vicinity of the MPB. Our study highlights the importance of local order-parameter mapping at the atomic scale and establishes a hitherto unobserved physical origin of spatially modulated phases existing in the vicinity of the MPB.
A new paradigm of domain wall nanoelectronics has emerged recently, in which the domain wall in a ferroic is itself an active device element. The ability to spatially modulate the ferroic order ...parameter within a single domain wall allows the physical properties to be tailored at will and hence opens vastly unexplored device possibilities. Here, we demonstrate via ambient and ultrahigh-vacuum (UHV) scanning probe microscopy (SPM) measurements in bismuth ferrite that the conductivity of the domain walls can be modulated by up to 500% in the spatial dimension as a function of domain wall curvature. Landau–Ginzburg–Devonshire calculations reveal the conduction is a result of carriers or vacancies migrating to neutralize the charge at the formed interface. Phase-field modeling indicates that anisotropic potential distributions can occur even for initially uncharged walls, from polarization dynamics mediated by elastic effects. These results are the first proof of concept for modulation of charge as a function of domain wall geometry by a proximal probe, thereby expanding potential applications for oxide ferroics in future nanoscale electronics.
The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains ...insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO(2) at a resolution of ∼100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.
Here we report on gas and vapor transport properties of ultra-thin graphene oxide (GO) membranes, with various C:O ratios. Graphene oxide nanosheets with an average lateral size of 800 nm and C:O ...ratio ranging from 2.11 to 1.81 have been obtained using improved Hummers’ method by variation of graphite:KMnO4 ratio. Thin-film selective layers based on the obtained graphene oxide have been spin-coated onto porous substrates. To extend the C:O range to 2.60, thermal reduction of GO membranes was applied. A decrease in C:O ratio leads to significant water vapor permeance growth to over 60 m3(STP)·m−2·bar−1·h−1 while the permeance towards permanent gases reduces slightly. According to the permeation and sorption measurements, a decisive role of H2O diffusivity has been established, while the water sorption capacity of the graphene oxide stays nearly independent of C:O ratio in GO. The result is supported by semi-empirical modeling which reveals diminution of H2O jump activation barriers with both increasing GO interlayer spacing and its oxidation degree. The height of the activation barriers was found to vary up to an order of magnitude within the entire range of relative humidity (0–100% RH), lowering significantly for strongly oxidized GO. Our results evidence the necessity of attaining maximum GO oxidation degree for improving water transport in GO, especially at low partial pressures.
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Memristive materials and devices, which enable information storage and processing on one and the same physical platform, offer an alternative to conventional von Neumann computation architectures. ...Their continuous spectra of states with intricate field-history dependence give rise to complex dynamics, the spatial aspect of which has not been studied in detail yet. Here, we demonstrate that ferroelectric domain switching induced by a scanning probe microscopy tip exhibits rich pattern dynamics, including intermittency, quasiperiodicity and chaos. These effects are due to the interplay between tip-induced polarization switching and screening charge dynamics, and can be mapped onto the logistic map. Our findings may have implications for ferroelectric storage, nanostructure fabrication and transistor-less logic.
In this study modification of AA2024 microstructure produced by friction drilling was investigated. To reveal the role of deformation, high temperature and friction on microstructure modification ...methods of optical and scanning electron microscopy and microhardness test were used. Different zones of material around friction drilling hole has a special characterization through grain size, volume fraction and size of incoherent second phase particles and microhardness. It has been found that deformation, high temperature and friction in friction drilling process lead to recrystallization of grain structure and dissolution of incoherent second phase particles due to strain-induced dissolution effect. Microhardness of recrystallized material has increased.
We explore ferroelectric properties of cleaved 2-D flakes of copper indium thiophosphate, CuInP2S6 (CITP), and probe size effects along with limits of ferroelectric phase stability, by ambient and ...ultra high vacuum scanning probe microscopy. CITP belongs to the only material family known to display ferroelectric polarization in a van der Waals, layered crystal at room temperature and above. Our measurements directly reveal stable, ferroelectric polarization as evidenced by domain structures, switchable polarization, and hysteresis loops. We found that at room temperature the domain structure of flakes thicker than 100 nm is similar to the cleaved bulk surfaces, whereas below 50 nm polarization disappears. We ascribe this behavior to a well-known instability of polarization due to depolarization field. Furthermore, polarization switching at high bias is also associated with ionic mobility, as evidenced both by macroscopic measurements and by formation of surface damage under the tip at a bias of 4 Vlikely due to copper reduction. Mobile Cu ions may therefore also contribute to internal screening mechanisms. The existence of stable polarization in a van-der-Waals crystal naturally points toward new strategies for ultimate scaling of polar materials, quasi-2D, and single-layer materials with advanced and nonlinear dielectric properties that are presently not found in any members of the growing “graphene family”.
A technology for evaluating the dynamic properties of mechanical vibration systems within the framework of structural and mathematical modeling methods with the use of dynamic characteristics of the ...structure of vibration fields of technological machines has been developed. We consider the problem of developing a mathematical model that allows us to correct the dynamic state depending on the system parameters based on local estimates of the properties of the vibration field. The ratio of reactions is used to evaluate the dynamic state of the vibration field. The coupling coefficient of external harmonic perturbations and the mass-inertia characteristic of a device for converting motion are considered as parameters of a mechanical oscillatory system. Based on a model with two degrees of freedom and two external influences, a detailed method for constructing mathematical models for evaluating local features of the vibration fields of technological machines is proposed. The obtained analytical expressions allow us to construct diagrams of the characteristics of mechanical oscillating systems depending on the parameters of the adjustment tools.
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•Few-layer graphene nanoflakes with domain size less than 50 nm were used as supports.•Supports with different types of dominating nitrogen species were synthesized.•Stability of ...nitrogen functional groups was investigated.•Catalysts supported on oxidized both pristine and doped supports were the most active.
Nitrogen-doped carbon nanomaterials show unique properties in catalysis both as an active component and as a support. The oxidized and N-doped graphene nanoflakes (GNFs) of low domain size (10–30 nm) have been studied in present work as supports for cobalt-based Fischer-Tropsch catalysts. Three supports with different types of dominating nitrogen species were synthesized and the effect of both the nature and localization of nitrogen species in the support on the structure and performance of 10 wt.% Co catalysts was investigated. Varying the synthesis technique and post-synthesis treatment, the cobalt particle size and hence the activity of catalyst can be tuned. The catalysts supported on oxidized pristine and N-doped GNFs were found to be the most active. Transformations of N-groups during catalyst preparation and reduction were observed. In the case of edge localization of N-groups the cross-linking of support particles was detected that led to the diffusion hindering and low CO conversion over corresponding catalyst.
The article focuses on the features of the dynamics of unilateral interactions of the elements of the brush-commutator unit of the traction electric motor of an electric locomotive within the scope ...of the problems of determining the conditions of motion without a gap interpreted as the quality factor of a current pick-up in dynamic loading processes. A mathematical model for the interaction of a brush, a collector surface and a pressing mechanism is proposed, which takes into account the possibility of contact failure depending on the parameters of the elements of the brush-commutator unit and the force factors including the effects of the vibrations of the traction motor body. The positivity of the complete reaction was used as the criterion for maintaining the contact. An analytical form of the conditions for the continuity of the contact between the elements of the brush-commutator unit is obtained on the basis of a comparison of the static and dynamic components of the complete reaction. The work shows the dependence of the analytical conditions of the continuity of the contact on the choice of the system parameters. It proposes a graphic-analytical method for determining the parameters ensuring continuity of the brush holder for the limiting stiffness of the pressing mechanism.
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