Interstitial Diffusion Research Articles

Influence of the POuN4-u structural units on the formation energies and transport properties of lithium phosphorus oxynitride: a DFT study.

The potential of mobile applications for digital networking is constantly increasing. A key challenge is to ensure a reliable and long-term power supply. One possible solution is the use of all-solid-state thin-film lithium batteries which use amorphous lithium phosphorus oxynitride (LIPON) as solid electrolyte. It is well known that the electrochemical properties of this material are related to the amorphous state, which correlates with the nitrogen content. Due to the difficulty of calculating amorphous structures using first principles methods, three different LIPON structure models are considered in this study and the influence of the anion POuN4-u sublattice on the Li vacancy and Li interstitial formation as well as on the lithium ion transport is highlighted. While for all three model systems the migration energies of the energetically preferred Li vacancies increase with increasing complexity of the anion POuN4-u sublattice only slightly from 0.38 eV to 0.55 eV, the migration energies for the energetically preferred Li interstitials decrease with increasing complexity of the anion POuN4-u sublattice from 0.68 eV to 0.38 eV. Thus, it was found that the energetically preferred lithium ion (Li vacancy and Li interstitial ion) transport mechanism in LIPON can be explained on the basis of the present POuN4-u structural units. In the presence of isolated PON3x- tetrahedra or periodic PO2N2 chains, the lithium vacancy diffusion dominates, whereas in the presence of periodic POuN4-u planes, the lithium interstitial diffusion becomes dominant.

Teaching online enantiosemia and word diffusion aspects during the coronavirus pandemics

The article’s primary goal is to demonstrate in the online teaching of language the philological aspects of the system and patterns of the occurrence of enantiosemia in the language to students. The article shows how language theoretical aspects can be taught in online learning. It also gives definitions of enantiosemic words for this purpose: to study their origin in the language system; to analyze the position in the text due to a change in syntactic meaning; tasks such as determining the nature of word formation, the study of the lexical stability. Enantiosemia occurs mainly in the form of interstitial diffusion. We use words in the form of opposite meanings during the speech, which are then stabilized and translated into a symmetrical second meaning. The study considers the secondary meaning transition through semantic analysis, contrasting, oppositional, and component analysis. We support the idea of developing the meanings of words being determined by the method of cognitive analysis. Thus, when instructing students to study the nature of enantiosis that acquire a new meaning that can be both stable or unstable in the language, it is necessary to do it in a context-sensitive manner and supplement the vocabulary.

Vascular and neurodegenerative imaging markers are associated with increased interstitial fluid diffusion in memory clinic patients

AbstractBackgroundDiffusion measurements in brain tissue may reveal various diffusion regimes reflecting different microstructural topologies, ranging from fast blood circulation, intermediate diffusion in wider interstitial spaces, to highly restricted inter‐ and intra‐cellular diffusion. Intravoxel incoherent motion MRI can detect an intermediate diffusion component, which is thought to be a proxy of brain tissue damage. This intermediate component might be relevant for studying amyloid clearance pathways, but currently remains incompletely understood. This study aims to increase our understanding of this intermediate component by studying associations with vascular (i.e. white matter hyperintensity (WMH) volume) and neurodegenerative (i.e. hippocampal atrophy) imaging markers in a sample of memory clinic patients, who display a wide range of cognitive abilities and variation in neurovascular and neurodegenerative pathology.MethodForty patients (Alzheimer’s disease dementia (AD, n=15), mild cognitive impairment (n=16), vascular cognitive impairment (VCI, n=9)) and 34 healthy controls underwent a 3T MRI protocol. The intermediate diffusion component was identified with spectral analysis using non‐negative least squares (Figure 1), and the contribution of the intermediate component to the signal in each voxel was determined by quantifying its volume fraction fint. The median of fint was determined for the following regions of interest (ROIs): cortical gray matter (GM), subcortical GM, WMH and normal appearing white matter (NAWM). A multivariate linear regression model incorporating age and gender was conducted to investigate group differences. Multiple linear regression was employed to investigate the association of fint per ROI with the vascular and neurodegenerative markers, additionally adjusting for total intracranial volume.ResultAD and VCI patients showed increased f int in GM and NAWM relative to controls (Figure 2). The fint was found to be associated to WMH and/or hippocampal volume, dependent on the brain region (Table 1).ConclusionThe intermediate component is associated with both vascular and degenerative markers, but this effect is region dependent. The group differences indicate a relation between fint and clinical phenotype. Brain regions where fint is affected by both vascular and degenerative markers show abnormally high fint in AD, which emphasizes the complexity to separate vascular and degenerative influences on AD pathology.

Grand-potential based phase-field model for systems with interstitial sites

Existing grand-potential based multicomponent phase-field model is extended to handle systems with interstitial sublattice. This is achieved by treating the concentration of alloying elements in site-fraction. Correspondingly, the chemical species are distinguished based on their lattice positions, and their mode of diffusion, interstitial or substitutional, is appropriately realised. An approach to incorporate quantitative driving-force, through parabolic approximation of CALPHAD data, is introduced. By modelling austenite decomposition in ternary Fe–C–Mn, albeit in a representative microstructure, the ability of the current formalism to handle phases with interstitial components, and to distinguish interstitial diffusion from substitutional in grand-potential framework is elucidated. Furthermore, phase transformation under paraequilibrium is modelled to demonstrate the limitation of adopting mole-fraction based formulation to treat multicomponent systems.

A Novel Approach for Understanding Heterogeneous Lithium-Ion Battery Aging Using Phase-Field Model

Aging due to capacity fade is a major cause of concern in the fast growing lithium-ion battery (LIB) industry. In particular, the evolution of Solid Electrolyte Interface (SEI) have been on the focus of battery scientist as one of the primary aging mechanism affecting the cycle life of the battery. According to the recent experimental studies, the formation of SEI possesses a heterogeneous morphology and it is attributed to the (i) anisotropic ionic mobility in the crystal and (ii) surface reactions governing the flux of ions across the electrode/electrolyte interface, depending on the local free energy difference (1, 2). In contrast to most previous study which utilise rough simplification on modelling of SEI growth, we employed a novel aging formulation that captures the heterogeneous multi-layered SEI morphology by including Cahn-Hilliard interstitial diffusion modelling approach coupled with Nernst-Planck and Butler-Volmer equations for mass transport and surface chemistry, respectively. Since the Cahn-Hilliard is able to captures the anisotropic surface intercalation reactions with depending the local free energy difference of active material, our numerical theory shows promising results for better explaining the cause of the heterogeneous SEI growths on active material surfaces than the classical diffusion-limited model. W. Huang, P. M. Attia, H. Wang, S. E. Renfrew, N. Jin, S. Das, Z. Zhang, D. T. Boyle, Y. Li and M. Z. Bazant, Nano letters, 19, 5140 (2019). P. Guan, L. Liu and X. Lin, Journal of The Electrochemical Society, 162, A1798 (2015). Figure 1

High Rate Transfer Mechanism of Lithium Ions in Lithium–Tin and Lithium–Indium Alloys for Lithium Batteries

The lithium–tin alloy electrode, as an artificial solid–electrolyte interphase (SEI) material with outstanding electrochemical properties, is promising to realize advanced next-generation lithium batteries. Experimental explorations on Li–Sn alloy have already achieved great success, while theoretical understanding on the mechanism of lithium-ion transport is still lacking. In this work, we carried out first-principles simulations and developed a theoretical methodology to reveal how a lithium ion diffuses in different lithium–tin phases and further elaborated the origin of low diffusion barriers. The simulation results indicate that two kinds of diffusion modes, interstitial and vacancy diffusion, will compete with each other with the increase in lithium concentration. Furthermore, the underlying mechanisms of direct hopping and coordinate process are also different in different Li–Sn/In phases. It is interesting to discover that during the lithiation process of alloy phases, the high-rate transport channel will gradually transform from the interstitial direct-hopping to vacancy mechanism and finally to the interstitial knock-off mechanism. This work provides a thorough theoretical understanding on lithium-ion transportation, further opening up the possibility of synthesizing or modifying SEI materials with enhanced Li conductivity in novel Li-ion battery designs.

Mechanism for Unipolar Reset in Negative Thermophoresis Resistive Memory Devices

Resistive switching behavior has been experimentally observed in Hafnia-based unipolar memory devices with negative thermophoresis. The traditional mechanism of RESET where the vacancy moves away from the filament fails to explain the reset behavior in these devices. We propose a model for RESET that involves diffusion of oxygen interstitials to break the vacancy-based filament in a region close to the top electrode as opposed to the center of the filament. Using Monte Carlo simulations, we establish the validity of the mechanism and show that it can model SET and retention.

Intrinsic defect migration in Be12Ti

Be12Ti is a leading candidate neutron-multiplier material for fusion breeder blankets; yet the evolution of the crystal defects under irradiation is poorly understood. Here, the migration of intrinsic defects in tetragonal Be12Ti was predicted using atomic scale computer simulation. Transport of titanium and beryllium through the interstitial, interstitialcy and vacancy-mediated models was considered, along with the migration of divacancy clusters, previously identified as important to the defect chemistry of Be12Ti. It was found that titanium defects exhibit much higher migration energies than beryllium for most migration pathways, leading to a dramatic difference in the self-diffusivity of the two species. Both beryllium vacancy and interstitial diffusion is close to isotropic with vacancy transport exhibiting the highest self-diffusion coefficient. Migration of beryllium di-vacancies is also isotropic with activation energy equal to that of isolated vacancies. The titanium interstitial exhibits significantly lower migration energy than its vacancy (1.00 eV and 6.75 eV respectively), with both mechanisms strongly anisotropic: the activation energy for [001] migration is at least 5 eV lower than other directions. Even the more exotic mixed titanium beryllium vacancy migration exhibits a much higher migration energy than [001] titanium interstitial transport. The framework used for predicting defect transport kinetics, including vacancy-mediated, interstitial and interstitialcy mechanisms, can be applied to any complex-structured intermetallic compound.

Canadian Postoperative Dependency Protocols Following Lower Limb Microvascular Reconstruction: A National Survey and Literature Review

Microsurgical free tissue transfer for lower limb reconstruction presents unique challenges in the postoperative period where dependency promotes interstitial fluid diffusion and reduced tissue perfusion. Management of flap edema, venous congestion, and ischaemic conditioning is critical for flap survival. Little evidence exists to guide postoperative protocols in the initiation and progression of lower extremity dangle, monitoring, and anticoagulation. We aim to describe current trends for postoperative dependency protocols by surveying Canadian microsurgeons. Plastic surgeons performing lower limb microvascular reconstruction at Fellow of The Royal College of Surgeons of Canada approved teaching institutions were administered a 17-question anonymous electronic survey. A literature review was conducted to identify protocols and consensus opinions in other jurisdictions. All respondents (n = 16) monitored flaps clinically, with conventional Doppler used by 13 respondents. Anticoagulation was employed by 15 of 16 respondents, and 9 of 16 used 2 or more agents. The most common agents were aspirin, followed by low-molecular-weight heparin. Significant variability existed in dangling protocols. Dependency was initiated at postoperative day (POD) 3 to 10 (mean POD: 6 ± 1.64 standard deviation), with intervals ranging from 5 to 20 minutes and frequencies ranging from 1 to 6 times per day. Nearly half allowed both increasing duration and frequency of dependency. Flap success rates were above 90%, and the median length of stay was 10 to 12 days. While flap success rates across the country are similar, no consensus exists for postoperative dependency protocols amongst Canadian microsurgeons. Prospective randomised controlled trials are warranted to evaluate early aggressive dependency protocols to reduce length of stay and cost.

Cation interstitial diffusion in lead telluride and cadmium telluride studied by means of neural network potential based molecular dynamics simulations

Using a recently developed approach to represent ab initio based force fields by a neural network potential, we perform molecular dynamics simulations of lead telluride and cadmium telluride crystals. In particular, we study the diffusion of a single cation interstitial in these two systems. Our simulations indicate that the interstitials migrate via two distinct mechanisms: through hops between interstitial sites and through exchanges with lattice atoms. We extract activation energies for both of these mechanisms and show how the temperature dependence of the total diffusion coefficient deviates from Arrhenius behaviour. The accuracy of the neural network approach is estimated by comparing the results for three different independently trained potentials.

Magnetic Volume Effect of Hydrogen Diffusion in Palladium

The electronic and magnetic properties of palladium hydrogen are investigated using first-principles spin-polarized density functional theory. By studying the magnetic moments and electronic structures of hydrogen atoms diffusing in face-centered cubic structure of transition metal Pd, we found that the results of magnetic moments are exactly the same in the two direct octahedral interstitial site-octahedral interstitial site diffusion paths-i.e. the magnetic moments are the largest in the octahedral interstitial site, and the magnetic moments are the lowest in saddle point positions. We also studied on the density of states of some special points, with the result that the density of states near the Fermi level is mainly contributed by 4d electrons of Pd and the change of magnetic moments with the cell volume in the unit cell of transition metal Pd with a hydrogen atom.

Thermal annealing of radiation defects in MgF2 single crystals induced by neutrons at low temperatures

Primary radiation defects in ionic solids consist of Frenkel defects – pairs of defects - anion vacancies with trapped electrons (F-type centers) and interstitial ions. Upon temperature increase after irradiation, the electronic F-type centers are annealed due to recombination with mobile interstitials. Analysis of the recombination (annealing) kinetics allows us to obtain important information on the interstitial migration. At high radiation doses more complex dimer (F2-type) centers are observed in several charge states, which are well distinguished spectroscopically. We analysed here available experimental kinetics of the F2-type center annealing in MgF2 in a wide temperature range (300–1000 K). The results of the electron, neutron and ion irradiation are compared.The phenomenological theory of the recombination kinetics of radiation defects takes into account the interstitial ion diffusion and recombination with the F2-centers as well as mutual sequential transformation with temperature growth of three types of experimentally observed dimer centers: F2 (1); F2 (2), F2 (3) (which differ tentatively by effective charges with respect to the host crystalline sites: 0, +1, +2).

Accelerated kinetic Monte Carlo: A case study; vacancy and dumbbell interstitial diffusion traps in concentrated solid solution alloys.

Vacancy and self-interstitial atomic diffusion coefficients in concentrated solid solution alloys can have a non-monotonic concentration dependence. Here, the kinetics of monovacancies and ⟨100⟩ dumbbell interstitials in Ni-Fe alloys are assessed using lattice kinetic Monte Carlo (kMC). The non-monotonicity is associated with superbasins, which impels using accelerated kMC methods. Detailed implementation prescriptions for first passage time analysis kMC (FPTA-kMC), mean rate method kMC (MRM-kMC), and accelerated superbasin kMC (AS-kMC) are given. The accelerated methods are benchmarked in the context of diffusion coefficient calculations. The benchmarks indicate that MRM-kMC underestimates diffusion coefficients, while AS-kMC overestimates them. In this application, MRM-kMC and AS-kMC are computationally more efficient than the more accurate FPTA-kMC. Our calculations indicate that composition dependence of migration energies is at the origin of the vacancy's non-monotonic behavior. In contrast, the difference between formation energies of Ni-Ni, Ni-Fe, and Fe-Fe dumbbell interstitials is at the origin of their non-monotonic diffusion behavior. Additionally, the migration barrier crossover composition-based on the situation where Ni or Fe atom jumps have lower energy barrier than the other one-is introduced. KMC simulations indicate that the interplay between composition dependent crossover of migration energy and geometrical site percolation explains the non-monotonic concentration-dependence of atomic diffusion coefficients.

Defect cluster and nonequilibrium gas bubble associated growth in irradiated UMo fuels – A cluster dynamics and phase field model

Irradiation examination shows that gas bubble swelling kinetics are much faster after irradiation-induced recrystallization than that prior to recrystallization in U-10 wt% Mo alloy (UMo) fuels. These kinetics imply that gas bubbles in coarse grains and small recrystallized grains have different growth behavior. For the first time, researchers developed a phase-field model of gas bubble evolution integrating microstructure-dependent cluster dynamics to study the gas bubble swelling behavior in the recrystallization zone of UMo fuels. Generation, diffusion, reaction, sink, emission, and clustering of vacancies and interstitials are described by the cluster dynamics model while a phase-field model is used to describe the evolution of nonequilibrium gas bubbles including nucleation and growth. With the coupled model, the effect of defect generation rate, clustering rate, interstitial emission, and sink rates on grain boundaries on the gas bubble evolution are systematically simulated. A set of model parameters (defect generation rate, clustering rate, interstitial emission, and sink rates) is determined by comparing measured and simulated gas bubble swelling kinetics. The results demonstrate that interstitial clustering is one of the important physical mechanisms that results in fast gas bubble swelling kinetics in the recrystallization zone. The developed model can also be extended to study the associated growth of defect and second-phase precipitates often observed in irradiated materials.

Insight into diffusion-rebonding of Nano-Al2O3 on Fe surface in high-temperature thermal energy storage system

Molecular dynamics simulations were carried out to investigate the diffusion-rebonding of nanoscale α-Al2O3 on the Bcc-Fe surface at high-temperature. The results indicated that the mutual diffusion occurred between Al2O3 and Fe in the temperature range of 498–1098 K. The diffusion modes of Fe and Al2O3 are confirmed as interstitial diffusion and surface diffusion, respectively. An amorphous layer was gradually formed at the interface due to diffusion and rebonding at the interface. The thickness of the amorphous layer extended with the temperature increasing. More importantly, because the Fe ions occupied the space of the Al2O3 by the strong diffusion effect induced by high temperature, the different Fe ions rebonded with Al and O to form the new coordination complexes such as AlnFem (AlFe, AlFe3, and Al6Fe) and FeO. The formation of these coordination complexes induced the phonons transporting in the scattering mode at the interface and resulted in the reduction of the mean free path of the phonon. Consequently, the thermal resistance of the interface remarkable increased, which deteriorated the thermal transport performance of the material.

Distinguishing interstitial and substitutional diffusion in grand-potential based phase-field model

Grand-potential based phase-field technique is often claimed to be an efficient approach for modelling phase transformation in multicomponent systems. Since this technique largely employs mole fraction to treat concentration, it is principally restricted to simulating microstructural evolutions which are exclusively governed by substitutional diffusion. In this work, an existing grand-potential model is re-formulated to encompass interstitial diffusion. The distinction between interstitial and substitutional diffusion is achieved by adopting molar number-density (mol/m3) based description of composition. The ability of the re-formulated approach to model phase transformation accompanying interstitial and substitutional diffusion is elucidated by simulating rather straightforward decomposition of austenite into ferrite in the ternary Fe-C-Mn system. Energy-density approximations that facilitate the incorporation of CALPHAD data in the present framework are delineated for general, and in particular for Fe-C-X alloy systems. Furthermore, phase-change under para-equilibrium, which can only be imposed through the re-formulated variant of grand-potential technique, is modelled and the resulting concentration profile is discussed in comparison to the outcomes of the conventional approach. Partitioning of carbon in constrained-carbon-equilibrium condition is consistently simulated in-line with its description.

Investigation of diffusion mechanism of beryllium in GaN

Diffusion mechanism of beryllium in gallium nitride was investigated by analyzing temperature-dependent diffusion profiles from an infinite source. Beryllium atoms were implanted into a high structural quality gallium nitride layer crystallized by halide vapor phase epitaxy on an ammonothermal gallium nitride substrate. Post-implantation annealing was performed at different temperatures, between 1000 °C and 1400 °C, under high nitrogen pressure. Beryllium profiles were analyzed in the as-implanted and annealed samples by secondary ion mass spectrometry. It was shown that the diffusion of the dopant results from the combination of two mechanisms: rapid interstitial and slow interstitial-substitutional diffusion. The pre-exponential factor as well as activation energy for both diffusion paths were determined. Moreover, from the characteristic features of beryllium depth profiles, the formation energies of gallium vacancy and beryllium in interstitial position were calculated and compared to the theoretical values.

The interstitial diffusion behaviors and mechanisms of boron in α-Ti and β-Ti: A first-principles calculation

For a better explanation of the growth mechanism of boride layer on Ti substrate, the interstitial diffusion behaviors and diffusion mechanisms of boron in α-Ti and β-Ti were investigated using first-principles calculations. The calculated results indicated that B atoms are more stable in octahedral site (O-site) of α-Ti and in tetrahedral site (T-site) of β-Ti, respectively. The interstitial diffusion pathway of B atom in α-Ti is O-O with a diffusion barrier of 0.84 eV, while that in β-Ti is T-T with a diffusion barrier of 0.78 eV. The lower diffusion barrier of B atom in β-Ti indicated that the diffusion of B atom in β-Ti is easier to arise. The electronic structures during the interstitial diffusion were discussed. Finally, the predicted diffusion coefficients were compared with the experimental ones.

The formation and accumulation of radiation-induced defects and the role of lamellar interfaces in radiation damage of titanium aluminum alloy irradiated with Kr-ions at room temperature

A transmission electron microscopy (TEM) specimen of a titanium aluminide (TiAl) alloy was irradiated in-situ, at the IVEM-TANDEM facility, with 1 MeV Kr ions to a maximum fluence of 1.25 × 1019 ions m−2 at room temperature. The irradiated microstructure was then investigated ex-situ using advanced analytical TEM in combination with TEM image simulations and molecular dynamics (MD) simulations. The TEM examination showed that dot-like defects first formed in both the α2-Ti3Al and γ-TiAl phases of the irradiated microstructure. With increasing irradiation dose planar defects formed and propagated within the γ phase, and most of the planar defects were accompanied by the dot-like defects. The TEM image simulations and MD irradiation simulations revealed that the origins of the dot-like and planar defects were interstitial clusters and stacking faults, respectively, and large interstitial clusters were surrounded by dislocation loops. The interstitial clusters formed and grew in the irradiated microstructure due to much faster diffusion of interstitials than that of vacancies at room temperature. Local stress concentrations increased near large interstitial clusters and lamellar interfaces, which resulted in the nucleation and propagation of stacking faults. Moreover, the configurations of the lamellar interfaces in the start microstructure were found to play an important role in the formation and accumulation of the radiation-induced interstitial clusters and stacking faults at room temperature.

Dynamical processes of interstitial diffusion in a two-dimensional colloidal crystal

In two-dimensional (2D) solids, point defects, i.e., vacancies and interstitials, are bound states of topological defects of edge dislocations and disclinations. They are expected to play an important role in the thermodynamics of the system. Yet very little is known about the detailed dynamical processes of these defects. Two-dimensional colloidal crystals of submicrometer microspheres provide a convenient model solid system in which the microscopic dynamics of these defects can be studied in real time using video microscopy. Here we report a study of the dynamical processes of interstitials in a 2D colloidal crystal. The diffusion constants of both mono- and diinterstitials are measured and found to be significantly larger than those of vacancies. Diinterstitials are clearly slower than monointerstitials. We found that, by plotting the accumulative positions of five- and sevenfold disclinations relative to the center-of-mass position of the defect, a sixfold symmetric pattern emerges for monointerstitials. This is indicative of an equilibrium behavior that satisfies local detailed balance that the lattice remains elastic and can be thermally excited between lattice configurations reversibly. However, for diinterstitials the sixfold symmetry is not observed in the same time window, and the local lattice distortions are too severe to recover quickly. This observation suggests a possible route to creating local melting of a lattice (similarly one can create local melting by creating divacancies). This work opens up an avenue for microscopic studies of the dynamics of melting in colloidal model systems.