Distribution Of Energy Barriers Research Articles

Capture efficiencies of point defects by 1/2 〈111〉 edge dislocations in tungsten using atomistic simulations

We systematically study the interaction behaviors between a point defect (PD) and two types of 1/2 〈111〉 {110} and 1/2 〈111〉 {112} edge dislocations using molecular dynamics (MD), elastic dipole tensor, and kinetic Monte Carlo (KMC) methods in tungsten (W). We first determine the capture region of a vacancy and four types of self-interstitial atoms (SIAs) by calculating their binding energies to both edge dislocations using MD. We then find anisotropic distributions of the diffusion energy barriers of PDs in dislocation systems employing the MD and elastic dipole tensor methods. Subsequently, we utilize the KMC method to obtain the lifetime of PDs and calculate the capture efficiencies of both edge dislocations to PDs at various temperatures and dislocation densities. Results show the capture efficiency of a vacancy decreases with increasing temperature, while it first increases and then decreases with increasing temperature for SIAs. As dislocation density increases, the capture efficiency of PDs increases. Ultimately, the swelling rate is estimated based on the capture efficiency and falls within the range of experimental data. The swelling rate increases first and then decreases with increasing temperature, and the maximum swelling rate occurs around 1200 K, while it increases with increasing the dislocation density. The present results are critical for understanding the interaction behaviors between PDs and 1/2 〈111〉 edge dislocations in W, which provide an essential database for large-scale simulation methods such as rate theory and phase-field simulations.

Constructing hierarchical MoS2/WS2 heterostructures in dual carbon layer for enhanced sodium ions batteries performance

The escalating global demand for clean energy has spurred substantial interest in sodium-ion batteries (SIBs) as a promising solution for large-scale energy storage systems. However, the insufficient reaction kinetics and considerable volume changes inherent to anode materials present significant hurdles to enhancing the electrochemical performance of SIBs. In this study, hierarchical MoS2/WS2 heterostructures were constructed into dual carbon layers (HC@MoS2/WS2@NC) and assessed their suitability as anodes for SIBs. The internal hard carbon core (HC) and outer nitrogen-doped carbon shell (NC) effectively anchor MoS2/WS2, thereby significantly improving its structural stability. Moreover, the conductive carbon components expedite electron transport during charge–discharge processes. Critically, the intelligently engineered interface between MoS2 and WS2 modulates the interfacial energy barrier and electric field distribution, promoting faster ion transport rates. Capitalizing on these advantageous features, the HC@MoS2/WS2@NC nanocomposite exhibits outstanding electrochemical performance when utilized as an anode in SIBs. Specifically, it delivers a high capacity of 415 mAh/g at a current density of 0.2 A/g after 100 cycles. At a larger current density of 2 A/g, it maintains a commendable capacity of 333 mAh/g even after 1000 cycles. Additionally, when integrated into a full battery configuration with a Na3V2(PO4)3 cathode, the Na3V2(PO4)3//HC@MoS2/WS2@NC full cell delivers a high capacity of 120 mAh/g after 300 cycles at 1 A/g. This work emphasizes the substantial improvement in battery performance that can be attained through the implementation of dual carbon confinement, offering a constructive approach to guide the design and development of next-generation anode materials for SIBs.

Ultrabroad distribution of multiple anelasticities in O-doped refractory multiprincipal element alloys

The Snoek anelastic internal friction (IF) peak due to stress-induced dipole ordering associated with interstitial atoms was well observed in IF curves of single-principal element alloys (SPEAs) as early as in the 1950s, however, its behavior remains elusive in multi-principal element alloys (MPEAs) to date. Here the temperature-dependent IF spectra of NbTiV0.5Zr refractory MPEAs with varying O contents were presented, and the analysis of these data indicates that for O-doped NbTiV0.5Zr MPEAs, the O addition triggers two anelastic IF peaks (the PO1 and PO2), corresponding to the O-Snoek-type relaxation in random solid solution (RSS) and local chemical ordering (LCO) structures, respectively. The half-peak width of the PO1 is 2–3 times broader than that for SPEAs, associated with the wide O migration energy barrier distribution in MPEAs. These phenomena show a striking contrast to the single and narrow Snoek-type peak observed for SPEAs. Our analysis further reveals an approximate linear correlation between the half-peak width of the Snoek-type peak and the mixing entropy. The introduction of O also shifts grain boundary relaxation peaks (PG) towards higher temperatures. Interestingly, high-temperature anomalous modulus changes were observed for the first time in TiV-based lightweight refractory MPEAs, which is suggested to be originated from the order reduction of the body-centered cubic (bcc) structure at elevated temperatures. Moreover, the 1 at.%O doped NbTiV0.5Zr MPEA with a favorable balance between the peak heights of the PO2 and PG, exhibits outstanding specific yield stress (SYS) among refractory MPEAs while maintaining an elongation as high as 20 %. This work provides not only a bridge between the anelastic behavior of SPEAs and MPEAs for upcoming studies and theories concerning bcc MPEAs with interstitial atoms, but contributes to the holistic design of bcc MPEAs with high strength and excellent ductility.

Structural confirmation of position isomers 2‐(2‐methylaminoprolyl)benzofuran and 5‐(2‐methylaminopropyl)benzofuran: a combined mass spectrometric and computational study

AbstractRationalePhenylethylamines are one of the most common types of new psychoactive substances, following synthetic cannabinoids and synthetic cathinones. They are regulated in many countries because of their strong hallucinogenic effects, which can cause serious nerve damage. There is a wide variety of phenylethylamines, exhibiting rapid renewal and extremely similar structures, therefore accurate qualitative analysis of isomers is a difficult problem in current drug analysis.MethodsThe dissociation pathways of the position isomers 2‐(2‐methylaminoprolyl)benzofuran (2‐MAPB) and 5‐(2‐methylaminopropyl)benzofuran (5‐MAPB) were investigated by gas chromatography–mass spectrometry and liquid chromatography coupled to high‐resolution quadrupole Orbitrap MS. The dissociation patterns of the phenethylamine‐based designer drugs 2‐MAPB and 5‐MAPB were explored and extended in this work based on MS combined with density functional theory studies.ResultsFor electron ionization mass spectrometry (EI‐MS) analysis, the dissociation patterns of 2‐MAPB were similar to those of 5‐MAPB. For electrospray ionization mass spectrometry (ESI‐MSn) analysis, the hydrogen atom on amino group was facile to form a intramolecular hydrogen bond with the oxygen atom on the parent nucleus of benzofuran in the structure of 2‐MAPB, leading to higher abundance of the product ion at m/z 58. However, there was a conjugated system between the positive charge formed by the cleavage of the 5‐MAPB side chain and the benzofuran ring, enabling the 5‐MAPB to generate a product ion at m/z 131. Computational study showed that energy barrier and spin density difference distribution jointly control the selective dissociation in EI‐MS, while different types of orbital interaction induced by intramolecular hydrogen bond led to different dissociation results in ESI‐MSn.ConclusionsThese different dissociation patterns could be used to distinguish 2‐MAPB from 5‐MAPB. This could assist forensic laboratories in the differentiation and characterization of potential isomers in these kinds of compounds, especially in mixtures.

On the Shear-Thinning of Alkanes

The approximate power law dependence of the apparent viscosity of liquids on shear rate is often argued to arise from a distribution of energy barriers. However, recent work on the Prandtl model, which consists of a point mass being dragged by a damped, harmonic spring past a sinusoidal potential, revealed a similar dependence of the friction on velocity as that of many liquids. Here, we demonstrate that this correlation is not only qualitative but can also be made quantitative over a broad temperature range using merely three dimensionless parameters, at least for alkanes, in particular n-hexadecane, at elevated pressure p. These and other observations made on our all-atom alkane simulations at elevated pressure point to the existence of an elementary instability causing shear-thinning. In addition, the equilibrium viscosity shows power law dependence on p near the cavitation pressure but an exponential dependence at large p, while the additional parameter(s) in the Carreau–Yasuda equation compared to other rheological models turn out justifiable.

Signature of functional enzyme dynamics in quasielastic neutron scattering spectra: The case of phosphoglycerate kinase.

We present an analysis of high-resolution quasi-elastic neutron scattering spectra of phosphoglycerate kinase which elucidates the influence of the enzymatic activity on the dynamics of the protein. We show that in the active state the inter-domain motions are amplified and the intra-domain asymptotic power-law relaxation ∝t-α is accelerated, with a reduced coefficient α. Employing an energy landscape picture of protein dynamics, this observation can be translated into a widening of the distribution of energy barriers separating conformational substates of the protein.

Time and temperature dependent magnetic viscosity experiments on Sr/Co nanoferrite particles

Magnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19–CoFe2O4 nanocomposites). The magnetic viscosity S = d M ( t ) / d l n ( t ), where M ( t ) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field H s a t considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes.

Er-doped gadolinium oxide nanoparticles for enhanced UV-VIS energy conversion: Structural features, optical properties and quantum efficiency

We present comprehensive study of the UV-VIS energy conversion in Gd2O3:Er nanoparticles. Based on our previous research, it was shown that Gd2O3:Er nanoparticles are promising for energy applications due to alternative channel of UV-VIS conversion through the Gd3+def →Er3+ energy transfer. However, a number of important issues, such as the influence of the structural features of the matrix (defectiveness and nonequivalence of cation positions) as well as the concentration of the activator ion on the processes of excitation-relaxation, were poorly understood. In this work we established and explained the mechanisms and regularities of UV-VIS energy conversion in Gd2O3:Er with a wide range of Er3+ concentration (0,25-8%).It was shown that with an increase in the Er3+ ion concentration, the mechanism of Gd3+def →Er3+ energy transfer changes from dipole-quadrupole interaction to exchange interaction due to a decrease in the average donor-acceptor distance. The evolution of the temperature dependences of Er3+ luminescence revealed two structurally (C2 and S6 positions in cubic Gd2O3) and energetically non-equivalent donor Gd3+def ions. It was determined that the distortions in the local environment of Gd3+def ions lead to the transformation of the barrier for emission quenching from discrete to dispersed distribution. The final efficiency of a complex UV-VIS conversion process was obtained accounting a number of factors: role of different channels of Er3+ excitation; bimodal distribution of energy barrier for emission quenching and influence of phonon states on non-radiative losses. The results demonstrate new possibilities for improving the functional characteristics of Gd2O3 nanoparticles for energy conversion devices. As one of the possible practical applications of the results of work, we made and tested prototypes of Si/Gd2O3:Er cells with enhanced efficiency of photovoltaic energy conversion.

Effect of alloying elements on elastic properties, generalized stacking fault energy, and critical resolved shear stress of Pd metal: A first principle study

Functional alloying elements (B, Si, P, Ti, V, Zn, Ga, In and Sn) and impurity elements (H and O) have an impact on the mechanical performance complexly. In order to clarify the effect of those elements, the elastic properties, generalized stacking fault energies and critical resolved shear stress of the Pd-X alloys were comprehensively analyzed by first-principle method. The variation of those elastic and ductile properties via alloying elements has been obtained. Crystal chemical analysis shows that the ionic bond between Pd and O determines the stability of O occupying tetrahedral site. Meanwhile, the energy barrier and dislocation distribution analysis support that the perfect dislocation will be decomposed to partial dislocations during the critical slip. According to electronic structure analysis, the increase of ductility (i.e., the decrease of unstable stacking fault energy along 112¯ directions) is attributed to the decrease of charge density on the slip surface. Moreover, a criterion, called misfit ratio R = |εs/εb|, is introduced to clarify major contribution of solid solution strengthening ΔτCRSS/c2/3 is lattice distortion effect or GSFE change effect caused by alloying elements.

Oxygen-enriched lignin-derived porous carbon nanosheets promote Zn2+ storage

Carbon-based zinc-ion capacitors (ZICs) have sparked intense research enthusiasm because of large power density, good rate capability and cycling stability. However, there is still a long way to go before they achieve commercial applications. Herein, oxygen-enriched lignin-derived porous carbon nanosheets (OLCKs) were prepared by one-step carbonization-activation method, and more O-containing functional groups were generated on the surface of the porous carbon by post-surface functionalization strategy. The self-doped N can change the electron distribution of carbon skeleton and decrease energy barrier of chemical absorption of Zn2+/H+. Meanwhile, the carbonyl group can significantly enhance the wettability of OLCKs. Furthermore, the diffusion-controlled reactions mainly exist at high and low potential ranges in CV curves, which demonstrates the occurred Faradaic reaction. Consequently, the assembled aqueous ZICs based on OLCKs demonstrate a capacity of 121.7 mAh/g at 0.3 A/g, energy density of 94.3 Wh kg−1 and good cyclic stability. Besides, the assembled Zn//PVA/LiCl/ZnCl2(gel)//OLCK4 ZIC can also achieve energy density of 134.4 Wh kg−1 at 0.1 A/g. This work provides a novel design strategy by incorporating abundant O and N-containing functional groups to enhance energy density.

Delayed elasticity of metallic glasses: Loading time and temperature dependences of the anelastic relaxation

One of the hallmarks of disordered matter is the large amplitude of the anelastic deformation, i.e., the fraction of reversible deformation that is not instantaneously recovered after the release of load but is delayed in time. In this paper, this delayed elasticity is studied for the glass-forming ${\mathrm{Zr}}_{46.25}{\mathrm{Ti}}_{8.25}{\mathrm{Cu}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{27.5}$ alloy by means of stress step and recovery experiments. Even at high temperatures, not far from the glass transition, the delayed elasticity can recover an important fraction of the deformation and endure for a long time. Analyzing the effects of loading time and waiting time on the strain evolution, we reveal the presence of an anelastic response with a timescale dependent on loading time and an invariant shape, which indicates the presence of a distribution of reversible relaxation modes following a ${\ensuremath{\tau}}^{\ensuremath{-}n}$ law with exponent $n$ between 0.5 and 1. The underlying distribution of energy barriers activated at different temperatures is accordingly shape invariant. Moreover, we found that a distribution of reversible modes corresponding to the high-frequency side of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{relaxation}$ peak can reproduce the experimental results. The results establish a direct link between the dynamical spectrum and the distribution of activation energies, revealing the origin of the transient creep and anelastic recovery behaviors of metallic glasses.

Magnetic relaxation of a system of interacting magnetic nanoparticles at finite temperature

We investigate the magnetic relaxation of a system of interacting single-domain magnetic nanoparticles, where the uniaxial energy density depends on temperature. Particles of different sizes are placed in random positions along a linear chain. For each value of temperature, the stochastic Landau–Lifshitz–Gilbert equation is numerically integrated. Applying an appropriate scaling function we determine the magnetic relaxation as a function of time and temperature as well as the energy barrier distribution of the system as a function of the mean distance between neighbor particles. We show that the typical energy barrier is not a monotonic function of the dipolar coupling. It decreases with the separation between particles until it reaches a minimum. For weaker dipolar interactions, the antiferromagnetic part could be responsible for enhancing the local uniaxial energy barriers. The decrease of the energy barrier for small values of the dipolar coupling was seen experimentally for the magnetoferritin nanoparticle.

In situ Electroactivated Fe‐NiOOH Nanoclusters on Carbon Quantum Dots for Efficient Large‐Scale Oxygen Production

The sluggish kinetics of oxygen evolution reaction (OER) seriously limits the development of water‐based energy devices due to the inevitable loss of activity at high current electrolysis. Herein, an in situ activation of the electrocatalyst of dual metal ions on carbon quantum dots (Fe‐NiOOH/CQDs) for the scalable oxygen production is reported. Through alternating the potential‐determining step and averaging energy barrier distributions of OER, Fe‐NiOOH/CQDs show excellent intrinsic OER performance with an extremely low Tafel slope of 35 mV dec−1 and the overpotential of 199 mV@10 mA cm−2. Meanwhile, the hydrophilicity and aerophobicity of Fe‐NiOOH/CQDs facilitate the rapid OH− diffusion and O2 detachment, resulting in an outstanding kinetics for large‐scale oxygen production. With an overpotential of 450 mV@1000 mA cm−2 and ultrahigh turnover frequency of 5.4 s−1, it is superior to most of the reported transitional‐metal‐based electrocatalysts. Thereby, a water splitting electrolyzer with Fe‐NiOOH/CQDs anode is assembled to demonstrate the promising reality.

Effect of the distribution of anisotropy constants on the magnetic properties of iron oxide nanoparticles

The distribution of shape anisotropy constants in two colloids of iron oxide nanoparticles has been measured from the distribution of particle elongations within each system. The results are in good agreement with the values calculated from a temperature decay of remanence measurement. For a fluid with a saturation magnetisation of 420 emu/cc and an average particle elongation of ∼ 1.3, the distribution of energy barriers is controlled by both the distribution of particle sizes and particle elongations. For a fluid with a saturation magnetisation of 320 emu/cc and a wide distribution of particle sizes, the energy barrier to reversal can be assumed to be controlled by the distribution of particle volumes. These results highlight the need to take into account the distribution of anisotropy constants when making predictions of the heating properties of assemblies of magnetic nanoparticles for hyperthermia applications.

Microscopic mechanisms of frictional aging

Frictional aging is observed at a wide range of length- and time-scales, and plays a crucial role in functioning of micro- and nanomachines, as well as in the nucleation and recurrence of earthquakes. Here, we developed an analytical model for description of frictional aging mediated by dynamical formation and rupture of microscopic interfacial contacts. The model accounts for the presence of various types of contacts at the frictional interface and exhibits three different aging regimes: (i) linear aging at short hold times, (ii) logarithmic (or logarithmic-like) aging for intermediate time scales and (iii) levelling off in the static friction for long hold times. It is demonstrated that the linear aging regime is a universal feature of frictional aging for the interfaces including various types of contacts, and the slope of variation of the static friction with the hold time depends on a distribution of energy barriers for contact formation. The conditions for the existence of a pronounced logarithmic aging regime, covering a long-time interval, have been established. Frictional aging has been found to manifest itself not only in slide-hold-slide measurements, but also in sliding experiments exhibiting stick-slip mode of motion, and a relationship has been established between these two regimes of aging. The predicted dependencies of frictional aging on the normal load and temperature are in good agreement with the experimental observations. Our work shows that experimental studies of load and temperature dependencies of aging, carried out over a wide range of time scales, offer promising opportunities for understanding the microscopic mechanisms of frictional aging and revealing the physical meaning of state variables that determine temporal evolution of friction described by phenomenological rate and state laws.

Deuteron magnetic resonance study of glyceline deep eutectic solvents: Selective detection of choline and glycerol dynamics.

Glyceline, a green solvent considered for various electrochemical applications, represents a multi-component glass former. Viewed from this perspective, the choline cation and the hydrogen bond donor glycerol, the two major constituents forming this deep eutectic solvent, were studied using nuclear magnetic resonance in a selective manner by means of suitably deuteron-labeled isotopologues. Carried out from far above to far below the glass transition temperature, measurements and analyses of the spin-lattice and spin-spin relaxation times reveal that the reorientational dynamics of the components, i.e., of glycerol as well as of chain deuterated choline chloride are slightly different. Possible implications of this finding regarding the hydrogen-bonding pattern in glyceline are discussed. Furthermore, the deuterated methyl groups in choline chloride are exploited as sensitive probes of glyceline's supercooled and glassy states. Apart from spin relaxometry, a detailed line shape analysis of the CD3 spectra yields valuable insights into the broad intermolecular and intramolecular energy barrier distributions present in this binary mixture.

Estimating ruggedness of free-energy landscapes of small globular proteins from principal component analysis of molecular dynamics trajectories.

The internal dynamics of biomolecules, and hence their function, is governed by the structure of their free-energy landscape. Early flash-photolysis experiments on myoglobin suggested that the free-energy landscapes of proteins are hierarchically structured, with a characteristic distribution of free-energy barriers which gives rise to anomalous diffusion. Analytical results have been derived for one-dimensional or high-dimensional hierarchical free-energy landscapes. Recent improvements in methods and computer performance enable generating sufficiently long molecular dynamics (MD) trajectories to extract dynamics information covering many orders of magnitude, such that the broad distributions of energy barriers of proteins become accessible to quantitative studies of intermediate dimensions. In this work, we present a nonequilibrium method to estimate barrier height distributions from microsecond-long MD simulations. It infers barrier height distributions from anomalous diffusion exponents derived from principal component analysis and by comparison to simple hierarchical lattice models. These models are d-dimensional lattices of states separated by free-energy barriers, the heights of which are distributed as p(ΔG)=1/γexp(-ΔG/γ). The parameter γ quantifies the "ruggedness" of the free-energy landscape in such models. We show that both parameters, i.e., ruggedness and effective dimensionality d, can be inferred from anomalous diffusion exponents. Assuming a similar dependency of anomalous diffusion exponents on γ and d for proteins, we estimate the ruggedness of the free-energy landscapes of 500 small, single-domain globular proteins between 15 and 20 kT per dimension with an estimated accuracy of 4.2 kT and dimensionality between 40 and 60 with an estimated accuracy of 10 dimensions. Remarkably, neither effective dimensionality nor the ruggedness correlates with protein size and both ruggedness and effective dimensionality are much smaller than the scatter of protein sizes. From this finding, we conclude that these two properties of the free-energy landscape of a protein are rather adapted to the particular function of each single protein and that, quite generally, are functionally relevant for globular proteins.

Rooting Zn into metallic Na bulk for energetic metal anode

Metallic Na with high theoretical capacity and low redox potential is an attractive anode material for high-energy rechargeable metal batteries. The poor wettability of Na on current collectors and the weak interaction between Na atoms lead to uneven plating/stripping of Na and dendrite formation. Here, we report an encouraging strategy to tackle these issues by rooting Zn into metallic Na bulk through a molten infusion process. The introduction of Zn not only tunes molten Na into highly sodiophilic Na(Zn) but also guides the uniform nucleation of Na through a much stronger interaction. As a result, smooth Na plating and stripping with a low energy barrier and homogeneous current distribution are simultaneously accomplished. Stable galvanostatic cycling over 3000 h in symmetric Na(Zn) cells and low voltage hysteresis below 15 mV at a rate of 5 mA cm−2 have been recorded. When coupled with a Na3V2(PO4)2O2F cathode, the Na(Zn)-Na3V2(PO4)2O2F full cell demonstrates an energetic performance, highlighting the strategy of rooting Zn into alkali metal bulk for rechargeable metal batteries.

Nonlinear and thermal effects in the absorption of microwaves by random magnets

We study the temperature dependence of the absorption of microwaves by random-anisotropy magnets. It is governed by strong metastability due to the broad distribution of energy barriers separating different spin configurations. At a low microwave power, when the heating is negligible, the spin dynamics is close to linear. It corresponds to the precession of ferromagnetically ordered regions that are in resonance with the microwave field. Previously, we showed [Phys. Rev. B 103, 214414 (2021)] that in this regime a dielectric substance packed with random magnets would be a strong microwave absorber in a broad frequency range. Here we demonstrate that on increasing the power, heating and over-barrier spin transitions come into play, resulting in the nonlinear behavior. At elevated temperatures the absorption of microwave power decreases dramatically, making the dielectric substance with random magnets transparent for the microwaves.

Water reduction on the facets of Fe(OH)2: an experimental and DFT study

The capacity of Fe(OH)2 to reduce H2O was limited by the predominant distribution of inert (001) facet and high energy barrier of H2O dissociation on acitive (100) facet.