Migration Barriers Research Articles

Unraveling the Enhanced Kinetics of Sr2Fe1+xMo1‐xO6‐δ Electrocatalysts for High‐Performance Solid Oxide Cells (Adv. Energy Mater. 48/2021)

Perovskites In article number 2102845, Xian-Zhu Fu and co-workers report that partial substitution of Mo by Fe in a perovskite of Sr2Fe1+xMo1−xO6−δ shifts up the O p band energy closer to the Fermi level, which lowers O vacancy formation as well as the O migration barrier energy, significantly accelerating the catalytic reaction kinetics in H2 oxidation and CO2 reduction reactions.

NH4+-based frameworks as a platform for designing electrodes and solid electrolytes for Na-ion batteries: A screening approach

The development of new high-performance materials can boost the implementation of sodium-ion batteries. In this work, we report on a data-driven two-step algorithm for searching novel electrodes and solid electrolytes with superior estimated Na+ transport properties based on the crystal chemistry concept of flexibility and adaptability of polyhedral host structures to different mobile ions during the ion exchange reaction at low temperatures. At the first stage, polyanion frameworks derived from compositionally suitable NH4+-containing inorganic compounds are screened to study the dimensionality of Na+ diffusion pathways and migration barriers via the Bond Valence Energy Landscapes (BVEL) method. At the second stage, the downselected frameworks are optimized and examined using Density Functional Theory (DFT), which was adapted for the first time for the isomorphous ion exchange to model and validate the expected fast Na+ ionic diffusion. Such a screening of Inorganic Crystal Structure Database (2020) yields almost 70 compounds with anticipated high Na+ ionic conductivity to serve as potential electrodes or solid electrolytes. As a result, new promising KTiOPO4-type NaFeSO4F electrode material and langbeinite-type NaZr2(PO4)3 electrolyte that can be obtained from the corresponding NH4FeSO4F and NH4Zr2(PO4)3 parental frameworks, respectively, reveal low migration barriers in three crystallographic directions as per Nudged Elastic Band calculations.

Why do people from wealthy countries migrate?

This study estimates the role of governance and institutions in bilateral migration between countries in the Organization of Economic Cooperation and Development (OECD) over the period 1996 to 2016. We estimate an extended random utility model of migration using pooled OLS, fixed effects, 2SLS, and PPML estimators. Our findings indicate that institutional quality plays a significant role in bilateral migration between the OECD countries. Political institutions are found to play a more important role compared to economic institutions. We also examine the moderating role of migration policy in fostering the nexus between the quality of institutions and bilateral migration, using three measures: the Migration Policy Index (MPI), and sub-sample analyses using both top OECD to OECD migration destinations and Schengen area countries. The Schengen country specific sub-sample analysis shows that if migration barriers are withdrawn, bilateral institutional quality differences lead to higher migration. However, estimated results based on the MPI and top OECD to OECD migration destinations do not show a significant role for pro-migration policy in strengthening the relationship between institutions and migration. The results are robust to different estimation methods, sub-sample analyses, and alternative specifications of the empirical model.

First-principles study of borophene/phosphorene heterojunction as anode material for lithium-ion batteries

It is urgent to explore high-capacity and efficient anode materials for rechargeable lithium-ion batteries. For borophene and phosphorene, two configurations are considered to form a heterojunction: twist angles of 0° (I) and 90° (II). There is a less degree of mismatch and larger formation energy in the formation of a B/P heterojunction, implying that borophene and phosphorene form the stable heterojunction. The heterojunctions of these two configurations demonstrate good conductivity, and the electrons near the Fermi level are mainly provided by borophene. Very importantly, the low energy barrier for interlayer migration of Li is observed in configuration I (0.14eV) and II (0.06 eV), and the migration of Li on the borophene and phosphorene side of the heterojunction still maintains its original energy barrier in bare monolayer. Moreover, the two configurations show the theoretical capacity as high as 738.69 and 721.86 mA h g−1, respectively, which is comparable to bare phosphorene. Furthermore, compared with bare phosphorene, the average voltage is greatly reduced after the formation of heterojunction. Hence, the overall electrochemical properties of the B/P heterojunction have been enhanced by combining the advantages of the individual phosphorene and borophene monolayers, which guarantees the B/P heterojunction as a good candidate for the anode material used in Li-ion batteries.

Does genetic differentiation underlie behavioral divergence in response to migration barriers in sticklebacks? A common garden experiment

Water management measures in the 1970s in the Netherlands have produced a large number of “resident” populations of three-spined sticklebacks that are no longer able to migrate to the sea. This may be viewed as a replicated field experiment, allowing us to study how the resident populations are coping with human-induced barriers to migration. We have previously shown that residents are smaller, bolder, more exploratory, more active, and more aggressive and exhibited lower shoaling and lower migratory tendencies compared to their ancestral “migrant” counterparts. However, it is not clear if these differences in wild-caught residents and migrants reflect genetic differentiation, rather than different developmental conditions. To investigate this, we raised offspring of four crosses (migrant ♂ × migrant ♀, resident ♂ × resident ♀, migrant ♂ × resident ♀, resident ♂ × migrant ♀) under similar controlled conditions and tested for differences in morphology and behavior as adults. We found that lab-raised resident sticklebacks exhibited lower shoaling and migratory tendencies as compared to lab-raised migrants, retaining the differences in their wild-caught parents. This indicates genetic differentiation of these traits. For all other traits, the lab-raised sticklebacks of the various crosses did not differ significantly, suggesting that the earlier-found contrast between wild-caught fish reflects differences in their environment. Our study shows that barriers to migration can lead to rapid differentiation in behavioral tendencies over contemporary timescales (~ 50 generations) and that part of these differences reflects genetic differentiation.Significance statementMany organisms face changes to their habitats due to human activities. Much research is therefore dedicated to the question whether and how organisms are able to adapt to novel conditions. We address this question in three-spined sticklebacks, where water management measures cut off some populations, prohibiting their seasonal migration to the North Sea. In a previous study, we showed that wild-caught “resident” fish exhibited markedly different behavior than migrants. To disentangle whether these differences reflect genetic differentiation or differences in the conditions under which the wild-caught fish grew up, we conducted crosses, raising the F1 offspring under identical conditions. As their wild-caught parents, the F1 of resident × resident crosses exhibited lower migratory and shoaling tendencies than the F1 of migrant × migrant crosses, while the F1 of hybrid crosses were intermediate. This suggests that ~ 50 years of isolation are sufficient to induce behaviorally relevant genetic differentiation.

Understanding enterprise data warehouses to support clinical and translational research: enterprise information technology relationships, data governance, workforce, and cloud computing.

Among National Institutes of Health Clinical and Translational Science Award (CTSA) hubs, effective approaches for enterprise data warehouses for research (EDW4R) development, maintenance, and sustainability remain unclear. The goal of this qualitative study was to understand CTSA EDW4R operations within the broader contexts of academic medical centers and technology. We performed a directed content analysis of transcripts generated from semistructured interviews with informatics leaders from 20 CTSA hubs. Respondents referred to services provided by health system, university, and medical school information technology (IT) organizations as "enterprise information technology (IT)." Seventy-five percent of respondents stated that the team providing EDW4R service at their hub was separate from enterprise IT; strong relationships between EDW4R teams and enterprise IT were critical for success. Managing challenges of EDW4R staffing was made easier by executive leadership support. Data governance appeared to be a work in progress, as most hubs reported complex and incomplete processes, especially for commercial data sharing. Although nearly all hubs (n = 16) described use of cloud computing for specific projects, only 2 hubs reported using a cloud-based EDW4R. Respondents described EDW4R cloud migration facilitators, barriers, and opportunities. Descriptions of approaches to how EDW4R teams at CTSA hubs work with enterprise IT organizations, manage workforces, make decisions about data, and approach cloud computing provide insights for institutions seeking to leverage patient data for research. Identification of EDW4R best practices is challenging, and this study helps identify a breadth of viable options for CTSA hubs to consider when implementing EDW4R services.

A DFT investigation into the possibility of using noble gas encapsulated fullerenes for Li storage

Density functional theory calculations are used to explore the Li storage capacity of Ngm endohedral C60 fullerenes (Ng = He, Ne, Ar, Kr, Xe; m = 1, 2). Formation energies of Ng endohedral fullerenes are negative, ranging from −2.65 to −13.11 kcal/mol (at the PBE/DNP level). The incorporation of Ng and Ng2 moieties into C60 enhances the adsorption energy of Li. The maximum adsorption energy of the Li atom on Xe2 encapsulated C60 is about −45 kcal/mol, which is 7% larger than that of on pure C60. The presence of Ng atoms lowers the energy barrier for Li migration to neighboring pentagon or hexagon rings.

Revisited Ti2Nb2O9 as an Anode Material for Advanced Li-Ion Batteries.

Ti2Nb2O9 with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g-1 corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g-1 has been observed practically. In this work, highly reversible capacity of 200 mAh g-1 with the average (de)lithiation potential of 1.5 V vs Li/Li+ is achieved for Ti2Nb2O9 with pseudo-2D layered morphology obtained via thermal decomposition of the NH4TiNbO5 intermediate prepared by K+→ H+→ NH4+ cation exchange from KTiNbO5. Using operando synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. Operando X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti4+/Ti3+ and Nb5+/Nb4+ reduction/oxidation within the whole voltage range. Li+ migration barriers for Ti2Nb2O9 along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. Ti2Nb2O9 synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material Li4Ti5O12 in the next generation of high-performance LIBs.

Effect of La vacancies on the oxide-ion conduction in lanthanum silicate apatites

La-excess compositions of lanthanum silicate apatites (La9.33+0.67xSi6O26+x or La9.33+0.67xSi6–0.5xO26; x > 0) exhibit higher oxide-ion conductivity than basic composition (La9.33Si6O26) due to smaller activation energies. On the contrary, the activation energies for oxide-ion conduction tend to increase with more La vacancies, less La content, at the La 4f site. However, the effect of La vacancies on the activation energy of oxide-ion conduction is not fully understood. In the present work, first-principles calculations are performed for La9.33+0.67xSi6O26+x (x = 0.0, 0.5, 1.0) to clarify the relationship between the amount of La vacancy at the La 4f site and the activation energy of oxide-ion migration in the O4 channel. It is found that the potential barrier of oxide-ion migration is extremely low in La10Si6O26 (x = 1.0) whereas that becomes higher with increasing the amount of La 4f vacancies. This is closely related to sizes of La 6h triangles that surround the O4 channel. In the presence of more La 4f vacancies, La 6h triangles tend to be more expanded than those in La10Si6O26. Since migrating oxide ions have attractive interactions with their surrounding La 6h ions, more expanded La 6h triangles lead to more energy costs for atomic displacements of the La 6h ions during the oxide-ion migration, resulting in their higher potential energy barriers. The effect of La 4f vacancies on the oxide-ion migration can be explained by such local atomic arrangements of La 6h and their interactions with migrating oxide ions.

Effect of the coexistence of active metals and boron vacancies on the performance of 2D hexagonal boron nitride resistance memory

First-principles calculations were carried out to calculate the formation energy, migration barrier and electronic properties of a resistive memory model based on hexagonal boron nitride (h-BN) in the presence of an active metal and a boron vacancy (VB) using density functional theory (DFT). Following the benchmark of the exchange correlation functional and the calculated parameters of monolayer h-BN, a model of a multilayer h-BN vertical stack with distribution states of SW-5577 defects was proposed. For four active metal dopants (Ti, Ag, Cu and Ni), a preference towards substitution sites (S1) with the lowest dopant formation energies (DFEs) was identified, which enhanced the formation of adjacent VB, especially for the nearest neighbour. Furthermore, a low concentration of Ti dopant in the closest location to the initial position of the migration path would drastically reduce the migration barrier of the VB between layers. Finally, Ti dopants with two and three VB neighbours in the same layer significantly improved the conductivity and the formation of conducting channels because of the improvement of charge distribution in the resistance model, which was demonstrated by DOS plots, band-decomposed charge density and Bader charge. Our present work can provide theoretical guidance for the rational design and device optimization of h-BN-based RRAM devices.

Revealing the Two-Dimensional Surface Diffusion Mechanism for Zinc Dendrite Formation on Zinc Anode.

Aqueous zinc-ion battery is regarded as one of the promising devices for large-scale energy storage systems owing to its high safety, cost-effectiveness, and competitive electrochemical properties. However, the dendrite growth on zinc metal anodes dramatically hinders its further practical applications, and the internal mechanism of dendrite evolution is still unclear. The introduction of a protective layer on the anode interface is an effective method to avoid zinc dendrite growth. Herein, a two-dimensional (2D) atomic surface diffusion mechanism is proposed to reveal the evolution of zinc deposition from tiny protrusion to dendrite under uneven electric and ionic fields. Further, the conductive copper nitride (CN) protective layer is constructed on the zinc metal anode by a facile and scalable magnetron sputtering approach. Their protective layer possesses a high zinc affinity and high diffusion barrier for zinc atom migration, leading to spacious nucleation, and uniform zinc deposition, thus significantly boosting the electrochemical stability. For the first time, the role of the restricted 2D atomic surface diffusion mechanism in inhibiting the formation of zinc tiny protrusion that induces uneven electric and ionic fields is revealed. This work can provide a novel insight for future research on dendrite-free zinc metal anodes by interfacial modification.

Li migration, nucleation and growth behavior regulated by a lithiophilic cobalt phosphide-doped carbon nanofibers derived ion/electron conductive framework

The uncontrollable Li dendritic plating and infinite volumetric expansion significantly plague the practical applications of lithium (Li) metal, which is regarded as the most promising high-energy-density anode material for rechargeable batteries. The well regulated Li-ion (Li+) flux distribution and Li deposition is the prerequisite for feasible Li-metal batteries. In this work, the Li migration, nucleation and growth behavior are investigated with a lithiophilic CoP-doped carbon nanofibers (CoP@CNF)-guided self-standing substrate. The high adsorption effect and low migration barrier of CoP to Li+ lead to the reversible conversion reaction between Li and CoP, enabling an even charge transportation and a homogeneous Li+ concentration gradient. The uniform nucleation and dense electrodeposition of Li over through the CoP@CNF is demonstrated via combined in-situ/ex-situ morphologic and electrochemical characterizations. Benefiting from the small nucleation and growth overpotential of Li, the symmetrical cell of CoP@CNF@Li can steadily operate under 0.5 mA cm−2 over 2000 h with a low voltage hysteresis of ca. 12 mV. When paired with a LiFePO4 cathode, a specific capacity exceeding 90 mAh g−1 up to 1000 cycles is achieved at 5 C (1 C = 170 mA g−1), demonstrating the dendritic Li suppression capability of the CoP@CNF@Li composite anode.

Radiation damage of MoAlB at elevated temperatures: Investigating MAB phases as potential neutron shielding materials

A new family of ternary nano-laminated compounds, MAB phases, are studied as a promising class of neutron shielding materials for applications within fusion reactors. The shielding capacity against high-energy neutrons was evaluated, and the damage tolerance of MoAlB against Si+ irradiation was investigated over the temperature range of RT- 600 °C. The linear attenuation coefficients of these materials over wide neutron-energy ranges imply that Mo(W)AlB have a high neutron shielding capacity. MoAlB shows a strong resistance to crack formation and excellent tolerance to amorphization under higher temperatures. The detailed thermal dynamic behaviors (reaction barrier and migration barrier) associated with the defects in MoAlB were studied through DFT calculations. Also, the lattice parameter changes are related to the formation of various point defects and the defect evolution evidenced by Rietveld refinement of the GIXRD and DFT calculations. MoAlB is confirmed to be a great candidate as a neutron shielding material.

Modulation of oxygen transport by incorporating Sb2Te3 layer in HfO2-based memristor

The oxygen transport plays an important role on the uniformity of the transition metal oxides (TMOS) memristors. Here, the effect of incorporating Sb2Te3 layer into TiN/HfO2/Pt memristor on oxygen transport has been systematically explored. The experimental results reveal that the memristor with Sb2Te3 incorporation at TiN/HfO2 interface has improved switching uniformity and memory window. Further theoretical calculations demonstrate that Sb2Te3 is a proper oxygen reservoir as oxygen possesses very low formation energy and migration barrier in Sb2Te3 with many vacancies. During the operation process, the Sb2Te3 will gain more oxygen from the HfO2 layer than TiN once the applied voltage reaches up to forming voltage, producing more oxygen vacancies (VOs) in the HfO2 layer, compared with the device without the Sb2Te3 layer. Thus, the VOs conductive filaments (CF) in the HfO2 layer will be thick, resulting in a decrease in the randomness of CF's formation/rupture and, in turn, improving the device uniformity. Our findings provide an in-depth understanding of the oxygen reservoir in TMOS memristors, which is of great significance for the design and development of memristors.

Redox performance of Fe2O3/Al2O3 oxygen carrier calcined at different temperature in chemical looping process

Iron-based oxygen carriers often underwent severe phase segregation in the process of chemical looping, resulting in the reduction of the cyclic performance of oxygen carriers. The phase segregation characteristics of Fe2O3/Al2O3 calcined at different temperature (900 °C, 1100 °C, 1300 °C) were investigated in this study. The obtained samples were recorded as 900-FeAl, 1100-FeAl and 1300-FeAl, respectively. XPS results showed that the surface oxygen vacancies of Fe2O3/Al2O3 increased with the increase of calcination temperature. In the redox cycles, the deactivation rate of the three samples were 5.57% (900-FeAl), 6.99% (1100-FeAl) and 31.69% (1300-FeAl), respectively. After 20 cycles, the 1300-FeAl presented serious surface sintering and the largest enrichment degree of surface Fe (137.05%). It can be inferred that the severe enrichment of surface Fe leads to the serious sintering, which aggravates the deactivation of the 1300-FeAl in cyclic reactions. The low calcination temperature (900 °C, 1100 °C) makes the Fe2O3/Al2O3 exhibit rich pore structure, which generates space barrier for the outward migration of Fe cation and inhibits the phase segregation of Fe2O3/Al2O3. The results of this study are of great significance to understand the phase segregation of iron-based oxygen carriers, and provide guiding value for the synthesis of high-performance iron-based oxygen carriers.

Molecular dynamics simulations on the interactions between basal edge dislocation and point defects in magnesium at low temperature

In this work, we performed molecular dynamics (MD) simulations on the interactions between a basal edge < a > dislocation and point defects including vacancies and self-interstitial atoms in magnesium. Simulation results suggest that both self-interstitial atoms and vacancies have a blocking effect on dislocation motion, but the blocking effect of vacancies is much weaker than that of self-interstitial atoms. During interactions, self-interstitial atoms are absorbed and move with dislocation, and the edge dislocation climbs after absorbing self-interstitial atoms. In contrast, vacancies cannot be absorbed. To explain these observations, the binding energy and migration energy are calculated. The binding energy of both vacancies and self-interstitial atoms increases as they approach the dislocation core, seemingly indicating that they can be absorbed. However, the migration barrier of a vacancy is found to be about two orders in magnitude higher than that of a self-interstitial atom. Therefore, only self-interstitial atoms are absorbed, while vacancies cannot.

Accessing Structural, Electronic, Transport and Mesoscale Properties of Li-GICs via a Complete DFTB Model with Machine-Learned Repulsion Potential.

Lithium-graphite intercalation compounds (Li-GICs) are the most popular anode material for modern lithium-ion batteries and have been subject to numerous studies—both experimental and theoretical. However, the system is still far from being consistently understood in detail across the full range of state of charge (SOC). The performance of approaches based on density functional theory (DFT) varies greatly depending on the choice of functional, and their computational cost is far too high for the large supercells necessary to study dilute and non-equilibrium configurations which are of paramount importance for understanding a complete charging cycle. On the other hand, cheap machine learning methods have made some progress in predicting, e.g., formation energetics, but fail to provide the full picture, including electrostatics and migration barriers. Following up on our previous work, we deliver on the promise of providing a complete and affordable simulation framework for Li-GICs. It is based on density functional tight binding (DFTB), which is fitted to dispersion-corrected DFT data using Gaussian process regression (GPR). In this work, we added the previously neglected lithium–lithium repulsion potential and extend the training set to include superdense Li-GICs (LiC6−x; ) and lithium metal, allowing for the investigation of dendrite formation, next-generation modified GIC anodes, and non-equilibrium states during fast charging processes in the future. For an extended range of structural and energetic properties—layer spacing, bond lengths, formation energies and migration barriers—our method compares favorably with experimental results and with state-of-the-art dispersion-corrected DFT at a fraction of the computational cost. We make use of this by investigating some larger-scale system properties—long range Li–Li interactions, dielectric constants and domain-formation—proving our method’s capability to bring to light new insights into the Li-GIC system and bridge the gap between DFT and meso-scale methods such as cluster expansions and kinetic Monte Carlo simulations.

The Adsorption behaviors of pristine MoS2 and N-MoS2 Monolayer: A First-Principles Calculation

First-principles calculations are carried out to analyze the adsorption behaviors of adatoms (H, O) and gas molecules (CO, NO2 and NH3) on pristine MoS2 and N-doped MoS2 monolayer. Compared to the H adsorption on pristine MoS2, the N doping effectively increases the H adsorption strength by shifting the most stable adsorbing site from the top of S atom to the top of N atom. But for O atom, the N doping shows ignorable influence on the adsorption behavior between the adatom and the substrate. Initially, the monolayer MoS2 is less sensitive to gas molecules CO, NH3 and NO2. After N doping, the adsorption sensitivity of N-doped MoS2 to CO changes little, but the adsorption sensitivity to NH3 and NO2 molecules is effectively enhanced as well as the adsorption energies of N-doped MoS2 with adsorbed NH3 (NO2). Moreover, the N-doped MoS2 with adsorbed CO, NH3 and NO2 always show magnetic characteristics. The migration paths and barrier energies of atom/molecules on monolayer of MoS2 and N-MoS2 are also investigated. The minimum diffusion energy barrier for NO2 on N-MoS2 is only 0.098 eV, which is lower than NO2 on monolayer MoS2 (0.273 eV). Therefore, N doping can effectively reduce the migration barrier of NO2 gas molecules on the MoS2.

Considering the Revolution

Considering the Revolution

Atomistic simulations of helium behavior at the Cu(111)/W(110) interface

Atomistic simulations including molecular dynamics and static simulations were conducted to investigate helium (He) behavior at the copper (111)/tungsten (110) (Cu(111)/W(110)) interface. Single He atoms are found to be trapped and aggregate between the first and second Cu monolayers along the interface, which acts thus as a defect sink, and tend to distribute along FCC/HCP Cu zones. Based on the calculation of the migration barrier and formation energy of interstitial He atoms, the sink traps He atoms from both sides, especially from the W layer. Once the He atoms are trapped in the sink at low temperatures, few could escape, which increases the He concentration and promotes the formation of larger He bubbles in the sink.