Misfit dislocations induced by lithium-ion diffusion in a thin film anode

According to the diffusion kinetics and heteroepitaxial strained layer theory, this paper presents a theoretical model to investigate the generation and distribution of misfit dislocations in a thin film anode under galvanostatic and potentiostatic operations. The results show that the nucleation and density distribution of misfit dislocations largely depend on the thickness of the diffused layer and insertion time. When the thickness is less than a certain critical value, the total strain energy in the electrode is almost insusceptible and yet reduced by misfit dislocations for that of going beyond the critical value. Under potentiostatic operation, the rise range and response speed of the dislocation density are greater and faster. A certain region immediately possesses much lower dislocation density under the electrode surface compared with the region below it. These quantitative results can provide a new perspective into relieving diffusion-induced stress by misfit dislocations with the purpose of improving the mechanical durability of lithium-ion batteries.     

PbTiO3/SrTiO3(010)异质界面上的周期性失配位错及电子富集

It is important to determine the effects of misfit dislocations and other defects on the domain structure, ferroelectricity, conductivity, and other physical properties of ferroelectric thin films to understand their ferroelectric and piezoelectric behaviors. Much attention has been given to ferroelectric PbTiO₃/SrTiO₃ or PbZr_0.2Ti_0.8O₃/SrTiO₃ heterointerfaces, at which improper ferroelectricity, a spin-polarized two-dimensional electron gas, and other physical phenomena have been found. However, those heterointerfaces were all (001) planes, and there has been no experimental studies on the growth of (010) PbTiO₃/SrTiO₃ heterointerface due to the 6.4% misfit between two materials. In this study, we selected an atomically flat (010) PbTiO₃/SrTiO₃ heterointerface grown using a two-step hydrothermal method as the research subject, and this is the first experimental report on that interface. Interfacial dislocations can play a significant role in causing dramatic changes in the Curie temperature and polarization distribution near the dislocation cores, especially when the size of a ferroelectric thin film is scaled down to the nanoscale. The results of previous studies on the effects of interfacial dislocations on the physical properties of ferroelectric thin films have been contradictory. Thus, this issue needs to be explored more deeply in the future. This study used aberration corrected scanning transmission electron microscopy (STEM) to study the atomic structure of a (010) PbTiO₃/SrTiO₃ heterointerface and found periodic misfit dislocations with a Burgers vector of a[001]. The extra planes at the dislocation cores could relieve the misfit strain between the two materials in the [001] direction and thus allowed the growth of such an atomically sharp heterointerface. Moreover, monochromated electron energy-loss spectroscopy with an atomic scale spatial resolution and high energy resolution was used to explore the charge distribution near the periodic misfit dislocation cores. The fine structure of the Ti L edge was quantitatively analyzed by linearly fitting the experimental spectra recorded at various locations near and at the misfit dislocation cores with the Ti³⁺ and Ti⁴⁺ reference spectra. Therefore, the accurate valence change of Ti could be determined, which corresponded to the charge distribution. The probable existence of an aggregation of electrons was found near the a[001] dislocation cores, and the density of the electrons calculated from the valence change was 0.26 electrons per unit cell. Based on an analysis of the fine structure of the oxygen K edge, it could be argued that the electrons aggregating at the dislocation cores came from the oxygen vacancies in the interior regions of the PbTiO₃. This aggregation of electrons will probably increase the electron conductivity along the dislocation line. The physics of two-dimensional charge distributions at oxide interfaces have been intensively studied, however, little attention had been given to the one-dimensional charge distribution. Therefore, the results of this study can stimulate research interest in exploring the influence of the interfacial dislocations on the physics of ferroelectric heterointerfaces.     

Strain fields at contacts between small particles

Stress fields between interacting small particles ( approximately 100 nm) have been investigated by transmission electron microscopy. The background for these TEM observations is discussed in terms of adhesion stress fields (due to surface forces), the action of an applied point force, possibly magnetic, and dislocations or misfit strains due to an unfavorable matching of crystal lattices at the grain boundary. A further explanation might be sought along the line "squeezed-in oxide" which can be visualized as a coherent particle or a dislocation loop. Accompanying theoretical calculations have been performed and compared with the experimental results.     

Structural anomaly of fine bismuth particles observed by ultra high-vacuum TEM

Structure anomaly of bismuth particle was found at critical size of 8.4 nm. The particles smaller than 8.4 nm had the rhombic structure, which transformed to cubic-like structure above the critical size. The cubic-like structure was surrounded by shell region consisting crystalline blocks of rhombic structure. The boundary between the core and the shell region formed coherent interface to accommodate their mismatch only by strain. On the other hand, we found a misfit dislocation at each gap between the rhombic blocks, which results due to the rhombic angle (87.6°) different from cubic angle. The critical size was discussed in terms of introduction and elimination of the misfit dislocations. Cubic-like structure was also discussed in terms of inner pressure by the surface stress, in comparison with the results of high pressure experiments on the bulk bismuth crystal.     

Analysis of a reversible five-point bending configuration based on a novel two-sense support

A novel two-sense support for flexural tests has been designed and manufactured in Ikerlan. The aim of this support is to do two-sense bending fatigue tests. In order to reduce the displacement corresponding to a given stress, a novel test configuration, designated as five-point bending, is modelled analytically. Basically, it is a three-point configuration with two supports at the ends that exert forces in the same sense as the applied load. In this way, a partial clamping is obtained that can be modelled by concentrated loads. The model has been checked carrying out quasi-static three-point and five-point bending tests at different spans in unidirectional carbon/epoxy composite specimens. Flexural modulus and the out-of-plane shear modulus have been obtained by linear regression in both cases, after having obtained experimentally the stiffness of the system.     

Dissociation Rate Kinetics in a Solid-Phase Flow Immunoassay

Abstract

Solid-phase displacement assays allow extremely fast analyses when performed under continuous flow conditions. Continuous dissociation of labeled antigen from the immobilized saturated antibodies occurs even in the absence of competing unlabeled antigen. This spontaneous dissociation creates more unoccupied antibody binding sites which affect the magnitude of the signal generated. In order to evaluate the impact of this phenomenon in more detail, we extended the law of mass action to solid-phase binding assays and analyzed the dissociation kinetics of labeled antigen under continuous flow conditions. The effect of the flow on the dissociation kinetics was determined by calculation of the apparent dissociation rate constants (k_d) which increase with an increase in the flow rate. These dissociation rate constants are approximately 20- to 30-fold lower than those obtained from displacement studies (i.e., in the presence of competing unlabeled antigen). The difference in the dissociation rate constants obtained in the two studies is most likely a function of the degree of reassociation. The results of this study provide a basis for better understanding antibody kinetics at solid-liquid interfaces under flow conditions.     

Fracture,fatigue and yielding of materials as a stochastic process

Conclusion It is very interesting that stochastic process model, paying no speculation on detailed atomic mechanisms, can be applied reasonably in many types of fracture and failure of metallic and non-metallic materials. Especially in the case of yielding of mild steel, the experimental results are in good agreement with the prediction of the theory as a stochastic process based on the present dislocation theory in terms of atomic mechanism. This indicates that general concepts of the stochastic process theory of yielding of mild steel as well as the dislocation theory of yielding are correct. The experimental data available at the present time appear not sufficient to evaluate the relative merits of the several atomic theories proposed which may be constructed by employing different detailed dislocation models. Consequently, in this respect it would be very valuable to investigate the scatter characteristics of delay time for the initiation of yielding of mild steel under constant applied stress to check whether such eqn. [1] or [4] exists in this case or not, and to study the frequency distribution of upper yield stress at the constant rate of stress application at low temperatures.     

Point-like impurity-dislocation interactions in smectic A liquid crystals

The displacement field created in the neighbourhood of a point-like impurity, its self-energy and point-like impurity-dislocation interaction are calculated for a smectic A liquid crystal in the approximation of small deformations. The binding energy of a point defect to an edge dislocation is also estimated. The use of the Peach-Kochler formula as a basis for the calculation of the dislocation interaction with other defects is discussed.     

Thermomechanical Buckling Analysis of the E&P-FGM Beams Integrated by Nanocomposite Supports Immersed in a Hygrothermal Environment

Due to the widespread use of sandwich structures in many industries and the importance of understanding their mechanical behavior, this paper studies the thermomechanical buckling behavior of sandwich beams with a functionally graded material (FGM) middle layer and two composite external layers. Both composite skins are made of Poly(methyl methacrylate) (PMMA) reinforced by carbon-nano-tubes (CNTs). The properties of the FGM core are predicted through an exponential-law and power-law theory (E&P), whereas an Eshelby–Mori–Tanaka (EMT) formulation is applied to capture the mechanical properties of the external layers. Moreover, different high-order displacement fields are combined with a virtual displacement approach to derive the governing equations of the problem, here solved analytically based on a Navier-type approximation. A parametric study is performed to check for the impact of different core materials and CNT concentrations inside the PMMA on the overall response of beams resting on a Pasternak substrate and subjected to a hygrothermal loading. This means that the sensitivity analysis accounts for different displacement fields, hygrothermal environments, and FGM theories, as a novel aspect of the present work. Our results could be replicated in a computational sense, and could be useful for design purposes in aerospace industries to increase the tolerance of target productions, such as aircraft bodies.     

Application of hydrogen peroxide encapsulated in silica xerogels to oxidation reactions

Hydrogen peroxide was encapsulated into a silica xerogel matrix by the sol-gel technique. The composite was tested as an oxidizing agent both under conventional and microwave conditions in a few model reactions: Noyori's method of octanal and 2-octanol oxidation and cycloctene epoxidation in a 1,1,1-trifluoroethanol/Na2WO4 system. The results were compared with yields obtained for reactions with 30% H2O2 and urea-hydrogen peroxide (UHP) as oxidizing agents. It was found that the composite has activity similar to 30% H2O2 and has a several advantages over UHP such as the fact that silica and H2O are the only products of the composite decomposition or no contamination by urea or its derivatives occurs; the xerogel is easier to heated by microwave irradiation than UHP and could be used as both an oxidizing agent and as solid support for microwave assisted solvent-free oxidations.     

Encapsulated oxide nanoparticles: the influence of the microstructure on associated impurities within a material

Simulation techniques have been used to explore how the microstructure of a material influences the nature of associated impurities embedded therein. We illustrate this by exploring four systems: BaO and CaO nanoparticles encapsulated within a ("perfect") MgO host lattice and SrO and MgO nanoparticles encapsulated within a ("microstructural") BaO lattice, which comprises a network of screw-edge dislocations. This study uses annealing techniques to generate energetically feasible nanoparticle structures and morphologies, dislocation networks, interfacial boundaries, and strain profiles. Specifically, the different encapsulated nanoparticles exhibit a range of morphologies, expose a variety of facets at the nanoparticle/host lattice interface, and are observed to rotate within the cavity they occupy inside the host lattice. The structure and nature of the nanoparticles reflect the lattice misfit between the nanoparticle and the host lattice. The study suggests also that there exists a "critical nanoparticle size", above which dislocations evolve.     

The validity of Cassie's law: a simple exercise using a simplified model

The contact angle of a macroscopic droplet on a heterogeneous but flat substrate is studied using the interface displacement model which can lead to the augmented Young-Laplace equation. Droplets under the condition of constant volume as well as constant vapor pressure are considered. By assuming a cylindrical liquid-vapor surface (meniscus) and minimizing the total free energy of the interface displacement model, we derive an equation which is similar but different from the well-known Cassie's law. Our modified Cassie's law is essentially the same as the formula obtained previously by Marmur [J. Colloid Interface Sci. 168 (1994) 40]. A few consequences from this modified Cassie's law are briefly described in the following sections of this paper. Several sets of recent experimental results seem to support the validity of our modified Cassie's law.     

Point-like impurity-dislocation interactions in smectic A liquid crystals

Abstract

The displacement field created in the neighbourhood of a point-like impurity, its self-energy and point-like impurity-dislocation interaction are calculated for a smectic A liquid crystal in the approximation of small deformations. The binding energy of a point defect to an edge dislocation is also estimated. The use of the Peach-Kochler formula as a basis for the calculation of the dislocation interaction with other defects is discussed.     

Synthesis and crystal structure determination of a new misfit compound: [(EuS)1.5]1.15NbS2

The crystal structure of the new misfit compound [(EuS)_1.5]_1.15NbS₂ has been determined via the composite approach. The structure is built up from three [EuS] layers (= slab noted ‘Q’) alternating with the [NbS₂] sandwich (= slab noted ‘H’) along the stacking direction (c axis). The cell parameters (Å) of this composite structure are: Q-part, a = 5.760(1), b = 5.780(1), c = 29.734(5); H-part, a = 3.317(1), b = 5.790(1), c = 14.859(4). Eu atoms located on the exterior sides of the Q-part show a quite regular hemi-octahedral coordination, whilst the inner Eu atoms show a distorted octahedral coordination. From bond valence calculations, one can assume that the outer Eu atoms are at the +II oxidation state and the inner Eu atoms at the +III state. The structure of the H-part appears very comparable to that found for other misfit compounds, i.e., Nb atoms in a trigonal prismatic coordination with S atoms, as for the binary NbS₂ itself.     

On the structure of bilayer condensed phases confined between crystalline walls of triangular symmetry

Grand canonical ensemble Monte Carlo simulation method is used to study the structure of Lennard-Jones fluids confined between the parallel walls, formed by the (111) planes of the face centered cubic crystal. Thin slit pores with a width allowing for the formation of only two atomic layers are considered. It is shown that the structure of confined solidlike phases is very sensitive to the pore width, the misfit between the size of adsorbate atoms and the size of surface lattice, as well as the corrugation of the surface potential. In particular, when the misfit between the adsorbate atoms and the surface lattice is very small, even a weakly corrugated surface potential highly stabilizes solidlike phases of triangular symmetry. On the other hand, in the case of large misfit the packing effects become a dominating factor and lead to the appearance of solidlike phases of different structures and symmetries.     

Atom movement on a dislocated surface

The standard picture of growth at a screw dislocation assumes that the movement of adatoms on a dislocation loop is the same as on an ideal plane. We have examined this proposition by investigating the movement of a single tungsten adatom on a W(110) plane intersected by a screw dislocation. Surprisingly enough, adatom movement was entirely different than on a normal (110) plane: the overall diffusivity was higher, and the mobility varied with the location of the adatom relative to the dislocation core. This study demonstrates that surface transport is strongly affected in the vicinity of dislocations.     

Effective Permittivity of a Multi-Phase System: Nanoparticle-Doped Polymer-Dispersed Liquid Crystal Films

This paper studies the effective dielectric properties of heterogeneous materials of the type particle inclusions in a host medium, using the Maxwell Garnet and the Bruggeman theory. The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, and developed for NP-doped PDLC films. The effective permittivity of the composite was simulated at sufficiently high frequency, where the permittivity is constant, obtaining results on its dependency on the constituents’ permittivity and concentrations. The two models are compared and discussed. The method used for simulating the doped PDLC retains its general character and can be applied for other similar multiphase composites. The methods can be used to calculate the effective permittivity of a LC composite, or, in the case of a composite in which one of the phases has an unknown permittivity, to extract it from the measured composite permittivity. The obtained data are necessary in the design of the electrical circuits.     

Charge regulation in protein ion-exchange chromatography: development and experimental evaluation of a theory based on hydrogen ion Donnan equilibrium

An extension of the stoichiometric displacement (SD) model for the ion-exchange adsorption of dilute proteins is developed which accounts for the effects of hydrogen ion Donnan equilibrium on the protein charge. The ability of the new model to fit retention data when the fluid phase pH is near the protein pI and the effects of hydrogen ion Donnan equilibrium are important is examined using four different proteins and four different column packings. The results indicate that the model is able to fit retention data using values for the protein pI and the change in protein charge with pH at the pI, i.e., (dz/dpH)pI, that are significantly closer to the values of these parameters determined by isoelectric focusing and acid-base titrametry in free solution, respectively, as compared to the values obtained by determining the characteristic binding change as a function of pH using the traditional stoichiometric displacement model. This suggests that when the fluid phase pH is near the protein pI, charge regulation is an important cause of the discrepancy between the electrical charge of a protein in free solution and the characteristic binding charge from the stoichiometric displacement model. The results also indicate that for the case where the fluid phase pH is near the protein pI, the new model accounts for the effect of charge regulation during protein ion-exchange adsorption more accurately than previous models in the literature.     

Structure and electronic transport properties of the Misfit layer compound (LaSe)1.14(NbSe2)2, „LaNb2Se5”︁

The new misfit layer compound (LaSe)_1.14(NbSe₂)₂ has been synthesized from the elements at 1050- and its structure has been determined by a composite approach. The structure has an alternating stacking sequence of [LaSe] and two [NbSe₂] layers along the c direction. The misfit of the two different layers is occurring along the a direction: a₁(LaSe)=6.0191 Å and a₂(NbSe₂)=3.4372 Å therefore yielding a ratio of 1.751 which is very close to 7/4. An investigation of electrical resistivity was done. The crystal shows superconducting properties at 5.3 K.     

A carbonate controlled-addition method for amorphous calcium carbonate spheres stabilized by poly(acrylic acid)s

Stable amorphous calcium carbonate (ACC) composite particle with a size-controlled monodispersed sphere was obtained by a new simple carbonate controlled-addition method by using poly(acrylic acid) (PAA) (Mw = 5000), in which an aqueous ammonium carbonate solution was added into an aqueous solution of PAA and CaCl2 with a different time period. The obtained ACC composite products consist of about 50 wt % of ACC, 30 wt % of PAA, and H2O. Average particle sizes of the ACC spheres increased from (1.8 +/- 0.4) x 102 to (5.5 +/- 1.2) x 102 nm with an increase of the complexation time of the PAA-CaCl2 solution from 3 min to 24 h, respectively. The ACC formed from the complexation time for 3 min was stable for 10 days with gentle stirring as well as 3 months under a quiescent condition in the aqueous solution. Moreover, the ACC was also stable at 400 degrees C. Stability of the amorphous phase decreased with an increase of the complexation time of the PAA-CaCl2 solution. No ACC was obtained when the lower molar mass PAAs (Mw = 1200 and 2100) were used. In the higher molar mass case (Mw = 25 000), a mixture of the amorphous phase and vaterite and calcite crystalline product was produced. The present results demonstrate that the interaction and the reaction kinetics of the PAA-Ca2+-H2O complex play an important role in the mineralization of CaCO3.