Octahedral Interstitial Sites Research Articles

The interaction between a positive muon and multiple quadrupolar nuclei

A positively charged muon implanted in copper sits at an octahedral interstitial site and experiences a magnetic dipolar coupling with six nearest-neighbour quadrupolar I = 3/2 copper nuclei. The resulting avoided level crossing resonance observed as a function of magnetic field provides a means of studying these interactions and understanding the effect of the electric-field gradient due to the muon acting on the quadrupolar nuclei. The effect is usually modelled by considering the interaction between the positive muon and a single copper nucleus, but the other five copper nuclei are equally important. By solving the problem in the full 2(2I + 1)6 = 8192-dimensional Hilbert space, we demonstrate the effect of these additional interactions.

The Site and High Field βNMR Properties of 8Li+ Implanted in α-Al2O3

We present high (> 2 T) magnetic field βNMR measurements of 8Li+ implanted in single crystals of sapphire, a commonly used backing material for other samples. From the well-resolved quadrupolar splitting, we extract the electric field gradient (EFG) at the implanted 8Li+ site. Comparison with supercell density functional theory calculations of the EFG allows us to identify the octahedral interstitial site as the most likely candidate. In contrast to the zero field βNQR spectra, where multiple singals are detected, only a single site is evident at high field. We discuss possible explanations for this discrepancy. The spin lattice relaxation is extremely slow (1/T 1 < 0.02 s−1 ) over a broad temperature range from 4 to 300 K, demonstrating that cross relaxation with the 27Al nuclear spins is quenched in such high magnetic fields.

Microscopic Mechanism of Enhanced Catalytic Activity for Ammonia Synthesis in Y5M3(M = Si/Ge) Electrides

Due to the importance of ammonia in modern agriculture, industry, scientific research, and so on, exploring a high-performance catalyst for ammonia synthesis at mild conditions is always highly desirable and will continuously be a hot research area. In recent years, electride catalysts have drawn considerable attention due to the presence of excess interstitial electrons. Among the known electride catalysts, the electride Y5Si3 is particularly interesting owing to its excellent catalytic activity in both air and water conditions. However, the underlying microscopic mechanism for the whole reaction process of the ammonia synthesis on the Y5Si3 surface remains unclear, in particular for the role played by the interstitial electrons. Here, through first-principles calculations, we have systematically studied the adsorption structures and energies of an atom (H and N) or a molecule (H2, N2, and NH3), the dissociation of H2 and N2 molecules, and the energy barriers for the formation of intermediate complexes such as NH and NH2 and the final NH3 on the Y5Si3(0001) surface. Our charge density analysis unambiguously demonstrates that the surface interstitial electrons play a very important role in facilitating the N2 dissociation as well as the formation of NH3 by providing necessary electrons that reduce the energy barriers. Moreover, we have carried out a comparative study on another isostructural and isoelectronic electride Y5Ge3. We find that the energy barriers in the rate-determining step on both electride surfaces are lower than that on Ru(0001), suggesting their good catalytic activities in synthesizing NH3. We further show that the conclusion remains unchanged by the presence of a N atom occupying the sublayer octahedral interstitial site.

First principles investigation of trapping and diffusion of fission gas in AnO2

The trapping of fission gases in AnO2 has been investigated using density functional theory. The behavior of fission gases varies with the size in these oxides, therefore He and Xe have been considered in this work. In ThO2 and UO2, the octahedral interstitial site has been found to be more stable than oxygen vacancy, while actinide vacancy is found most stable site for He in all three oxides. For Xe, an oxygen vacancy is a more stable site than an octahedral interstitial site and actinide vacancy is the most stable site in these oxides. Our results indicate that He is much more mobile than Xe in these oxides.[copyright information to be updated in production process]

Nanoscale Iron Redistribution during Thermochemical Decomposition of CaTi1-x Fe x O3-δ Alters the Electrical Transport Pathway: Implications for Oxygen-Transport Membranes, Electrocatalysis, and Photocatalysis.

Potential applications of the earth-abundant, low-cost, and non-critical perovskite CaTi1-x Fe x O3-δ in electrocatalysis, photocatalysis, and oxygen-transport membranes have motivated research to tune its chemical composition and morphology. However, investigations on the decomposition mechanism(s) of CaTi1-x Fe x O3-δ under thermochemically reducing conditions are limited, and direct evidence of the nano- and atomic-level decomposition process is not available in the literature. In this work, the phase evolution of CaTi1-x Fe x O3-δ (x = 0-0.4) was investigated in a H2-containing atmosphere after heat treatments up to 600 °C. The results show that CaTi1-x Fe x O3-δ maintained a stable perovskite phase at low Fe contents while exhibiting a phase decomposition to Fe/Fe oxide nanoparticles as the Fe content increases. In CaTi0.7Fe0.3O3-δ and CaTi0.6Fe0.4O3-δ, the phase evolution to Fe/Fe oxide was greatly influenced by the temperature: Only temperatures of 300 °C and greater facilitated phase evolution. Fully coherent Fe-rich and Fe-depleted perovskite nanodomains were observed directly by atomic-resolution scanning transmission electron microscopy. Prior evidence for such nanodomain formation was not found, and it is thought to result from a near-surface Kirkendall-like phenomenon caused by Fe migration in the absence of Ca and Ti co-migration. Density functional theory simulations of Fe-doped bulk models reveal that Fe in an octahedral interstitial site is energetically more favorable than in a tetrahedral site. In addition to coherent nanodomains, agglomerated Fe/Fe oxide nanoparticles formed on the ceramic surface during decomposition, which altered the electrical transport mechanism. From temperature-dependent electrical conductivity measurements, it was found that heat treatment and phase decomposition change the transport mechanism from thermally activated p-type electronic conductivity through the perovskite to electronic conduction through the iron oxide formed by thermochemical decomposition. This understanding will be useful to those who are developing or employing this and similar earth-abundant functional perovskites for use under reducing conditions, at elevated temperatures, and when designing materials syntheses and processes.

The interaction of oxygen with the γ-U (001) and (110) surfaces: An ab initio study

The reactions of the γ-U (001) and (110) surfaces in contact with O2 were investigated by density functional theory (DFT), ab initio thermodynamic methods and ab initio molecular dynamics simulations (AIMD). The adsorption of the O atom and O2 molecule on the (001) and (110) surfaces and subsurface are first studied, which provides insights into the adsorption, dissociation, and diffusion of O2 on the surfaces. Furthermore, the effects of coverages on surface adsorption are considered to help us further understand surface oxidation corrosion. Based on the above research, we can speculate on the initial process of surface corrosion: 1. O2 molecules in the atmosphere first approach the U surface in the form of physical adsorption; 2. O2 molecules dissociate into O atoms on the surface; 3. O atoms diffuse on the surface after overcoming a small energy barrier and eventually occupy hollow (H) sites; 4. O atoms penetrate from the H sites to the subsurface; 5. The diffusion of O atoms inside the metal is more likely to be carried out by octahedral interstitial sites. Moreover, the adsorption phase diagrams indicate that O2 will readily react with U even under ultra-high vacuum conditions, which is consistent with the experimental results.

Kinetics study of ions in conductive filament growth process of electrochemical metallization resistive memory

&lt;sec&gt;In this work, a system of modified Mott-Gurney differential equations is based on Arrhenius’ law and the overpotential theory of ionic motion in bipolar electrochemical metallization (ECM) resistive devices. The average displacement of ions is solved by the modified Mott-Gurney equation. Then, the relation between the average displacement and the growth length of the conductive filament is obtained by a geometric model based on cells. The equation of applied voltage versus Forming/Set time and the equation of length of conductive filament growth versus time are deduced by using this relation.&lt;/sec&gt;&lt;sec&gt;In this work, an algorithm for extracting kinetic parameters of ions in a bipolar ECM device is also proposed. By using this algorithm, the characteristics of the applied voltage versus Forming/Set time for Ag/&lt;i&gt;γ&lt;/i&gt;-AgI/Pt, Ag/TiO&lt;sub&gt;2&lt;/sub&gt;/Pt, Ag/GeS&lt;sub&gt;2&lt;/sub&gt;/W, and Cu/SiO&lt;sub&gt;2&lt;/sub&gt;/Au devices are calculated and the calculation results are consistent with experimental data. It is found that in the Forming/Set process, the jump step of silver ion is the lattice constant along the &lt;i&gt;c&lt;/i&gt; direction of a unit cell of the crystal for TiO&lt;sub&gt;2&lt;/sub&gt; and the lattice constant of the cubic, &lt;i&gt;a&lt;/i&gt;, for &lt;i&gt;γ&lt;/i&gt;-AgI. These results are explained in the following. In a unit cell of the two crystals there are some tetrahedral and octahedral interstitial sites. The cationic motion path consists of alternating octahedral and tetrahedral sites or some octahedral sites. The cation jumps from tetrahedron to octahedron to tetrahedron, etc. in the &lt;i&gt;γ&lt;/i&gt;-AgI with coplanar polyhedron and from octahedron to octahedron in the TiO&lt;sub&gt;2&lt;/sub&gt; with edge shared octahedron. In GeS&lt;sub&gt;2&lt;/sub&gt; crystal, it is found that the jump step of silver ions is the lattice constant in the &lt;i&gt;c&lt;/i&gt; direction of a unit cell. Owing to the periodicity of the lattice, the pathways of the ion motion in the three materials can be expressed by a periodic potential barrier each. For the jump situation of the copper ion in amorphous SiO&lt;sub&gt;2&lt;/sub&gt;, the jump step of copper ions is calculated to be 1.57 times the length of the O—O bond, and the jump pathway can also be explained by a periodic potential barrier.&lt;/sec&gt;&lt;sec&gt;By introducing the cosine potential barrier, the ionic activation frequency, potential barrier height, ionic mobility and diffusion coefficient, and characteristics of the conductive filament growth versus time in several devices are calculated. The criteria of selecting dielectric materials for bipolar ECM devices are discussed by using these data. It is found that the standards for selecting dielectric materials of bipolar ECM devices are the ion activation energy ≤0.5 eV, preferably between 0.1–0.2eV, and the DC conductivity as close to 10&lt;sup&gt; –4&lt;/sup&gt; Ω&lt;sup&gt;–1&lt;/sup&gt;·cm&lt;sup&gt;–1&lt;/sup&gt; as possible.&lt;/sec&gt;

Interstitial diffusion of hydrogen in M[formula omitted]C[formula omitted] (M=Cr,Mn,Fe)

To increase the understanding of the role of carbide precipitates on the hydrogen embrittlement of martensitic steels, we have performed a density functional theory study on the solution energies and energy barriers for hydrogen diffusion in orthorhombic M7C3 (M = Cr, Mn, Fe). Hydrogen can easily diffuse into the lattice and cause internal stresses or bond weakening, which may promote reduced ductility. Solution energies of hydrogen at different lattice positions have systematically been explored, and the lowest values are -0.28, 0.00, and 0.03 eV/H-atom for Cr7C3, Mn7C3, and Fe7C3, respectively. Energy barriers for the diffusion of hydrogen atoms have been probed with the nudged elastic band method, which shows comparably low barriers for transport via interstitial octahedral sites for all three systems. Analysis of the atomic volume reveals a correlation between low solution energies and energy barriers and atoms with large atomic volumes. Furthermore, it shows that the presence of carbon tends to increase the energy barrier. Our results can explain previous experimental findings of hydrogen located in the bulk of Cr7C3 precipitates and provide a solid basis for future design efforts of steels with high strength and commensurable ductility.

Defect-Induced Atomic Arrangement in CoFe Bimetallic Heterostructures with Boosted Oxygen Evolution Activity.

Three CoFe-bimetallic oxides with different compositions (termed as CoFeOx -A/N/H) are prepared by thermally treating metal-organic-framework (MOF) precursors under different atmospheres (air, N2, and NaBH4 /N2 ), respectively. With the aid of vast oxygen vacancies (Ov ), cobalt at tetrahedral sites (Co2+ (Th)) in spinel Co3 O4 is diffused into interstitial octahedral sites (Oh) to form rocksalt CoO and ternary oxide CoFe2 O4 has been induced to give the unique defective CoO/CoFe2 O4 heterostructure. The resultant CoFeOx -H exhibits superb electrocatalytic activity toward water oxidation: overpotential at 10mA cm-2 is 192mV, which is 122mV smaller than that of CoFeOx -A. The smaller Tafel slope (42.53mV dec-1 ) and higher turnover frequency (785.5 h-1 ) suggest fast reaction kinetics. X-ray absorption spectroscopy, ex situ characterizations, and theoretical calculations reveal that defect engineering effectively tunes the electronic configuration to a more active state, resulting in the greatly decreased binding energy of oxo intermediates, and consequently much lower catalytic overpotential. Moreover, the construction of hetero-interface in CoFeOx -H can provide rich active sites and promote efficient electron transfer. This work may shed light on a comprehensive understanding of the modulation of electronconfiguration of bimetallic oxides and inspire the smart design of high-performance electrocatalysts.

Helium Stability and its Interaction with H in B2‐FeAl: A First‐Principles Study

Helium stability and its contribution to H blistering resistance in B2‐FeAl are investigated by a density functional theory (DFT) method, and the results obtained are compared with the H interaction with a Fe vacancy (VFe) in FeAl. He is more energetically favorable to occupy a VFe site, forming a He substituent (HeFe), in comparison with H occupying the first‐nearest‐neighbor (1NN) octahedral interstitial site of VFe in FeAl. At most, six H atoms can be trapped in the vicinity of HeFe one by one, forming HeFe–nH complexes (n is the number of trapped H atoms), similar to the case of VFe in the formation of VFe–nH complexes. HeFe–5H is the main species among the HeFe–nH complexes, whereas VFe–6H is the dominant one in the VFe–nH complexes. No H2 molecule forms inside the cluster unit of the HeFe–5H complex, due to the H–H repulsion caused by He. Strategies for H blistering resistance in iron aluminides are thus proposed.

First-principles insight of hydrogen dissolution and diffusion properties in γ-Al2O3

First-principles theory is applied to identify the structure of γ-Al2O3 first. Then, hydrogen dissolution and diffusion behavior was further studied to reveal the reason that permeation reduction factor (PRF) of γ-Al2O3 is lower than that of α-Al2O3. Our calculations show that the formation energy for Al vacancy at the octahedral interstitial site (VAl−OIS−3) is lower than that at the tetrahedral interstitial site (VAl−TIS−3), and are far lower than those of other defects in both defective spinel and non-spinel γ-Al2O3. Thus, the stability of VAl−OIS−3 is higher than that of VAl−TIS−3 in both Al-rich and O-rich environments. However, when hydrogen atoms are introduced into γ-Al2O3, the stability of [VAl-TIS-H]−2 is higher than that of [VAl-OIS-H]−2 in the defective spinel γ-Al2O3 structure, while the opposite is true for the non-spinel γ-Al2O3 structure. The vibrational frequencies for OH− in [VAl-TIS-H]−2 and [VAl-OIS-H]−2 for defective γ-Al2O3 are calculated to be 3608 cm−1 and 3374 cm−1, respectively, which is in excellent agreement with the infrared (IR) absorption peaks observed at ∼3500 and ∼3300 cm−1. The defective spinel model is more suitable for describing the γ-Al2O3 structure. In defective spinel γ-Al2O3, there are many native Al vacancies, which are arranged in a straight line along the [21¯1¯0] direction. The migration barrier for H diffusion along these native Al vacancies is so low that these Al vacancies can provide a rapid diffusion channel for H. Thus, the permeability of H in γ-Al2O3 is much higher than that in α-Al2O3 leading to a lower permeation reduction factor (PRF). Our results can provide not only a sound theoretical explanation for the low PRF of γ-Al2O3 but also a direction to improve the efficiency in preventing H permeation through FeAl/Al2O3 tritium permeation barriers (TPBs).

The bonding of H in Zr under strain

Accurate computer simulation is important for understanding the role of irradiation-induced defects in zirconium alloys found in nuclear reactors. Of particular interest is the distribution and trapping of hydrogen, and the formation of zirconium hydride. These simulations require an accurate representation of Zr-H bonding in order to predict the behaviour of H around atomic-scale defects, dislocation lines, and dislocation loops. Here we explore the bonding of H in Zr under strain, how well it is represented by state-of-the-art Embedded Atom Method (EAM) potentials, and what physics is needed for an accurate representation in a Linear Combination of Atomic Orbitals (LCAO) Density Functional Theory (DFT) framework. For H in dilute solution under hydrostatic strain in the range -10% to +10%, solution energies and Zr-H bond lengths computed using EAM potentials are found to be in poor agreement with plane-wave DFT results. We note that the bond lengths are in a poor agreement even in equilibrium. LCAO basis sets are used to explore the importance of electron distribution around H atoms, and the transfer of electrons between H and Zr. The electron distribution around H atoms is found to be important to the explanation of the difference between octahedral and tetrahedral interstitial sites for H, with H in a tetrahedral site having very similar bonding to H in zirconium hydrides. The interatomic electron transfer has a smaller impact but is needed for maximum accuracy.

Distinct nitriding behaviors of γ and γ′ phases in Ni-based superalloys: A first-principles study

The diffusion of nitrogen through γ(Ni)/γ'(L12-Ni3Al) interface in Ni-based superalloys was investigated based on first-principles calculations and the different nitriding behaviors of γ matrix and γ' precipitate were determined. At the interface, nitrogen atoms prefer to occupy the 6-Ni octahedral interstitial site with a large physical volume rather than the octahedral site constituted by Ni and Al with good chemical affinity. This indicates that γ matrix can provide more trapping sites for nitrogen atom than γ' precipitate. Moreover, the migration energy barrier of N crossing the (002)γ/γ' coherent plane is higher than that in γ phase. Nitrogen atoms can move into γ' phase unless the diffusion front has higher nitrogen concentration and O4 * (5Ni-Al octahedral site) is occupied. Inside the γ' matrix, nitrogen atoms are also easily trapped by the 6-Ni octahedral interstitial site, but their escape rates are much lower. It is the potential barrier role of the (002)γ/γ’ coherent plane and the low diffusion ability of N in γ' that are responsible for the unfavorable nitriding behavior of γ' phase in Ni-based superalloys.

Influence of Nonmetallic Interstitials on the Phase Transformation between FCC and HCP Titanium: A Density Functional Theory Study

In addition to the common stable and metastable phases in titanium alloys, the face-centered cubic phase was recently observed under various conditions; however, its formation remains largely unclarified. In this work, the effect of nonmetallic interstitial atoms O, N, C and B on the formation of the face-centered cubic phase of titanium was investigated with the density functional theory. The results indicate that the occupancy of O, N, C and B on the octahedral interstitial sites reduces the energy gap between the hexagonal-close-packed (HCP) and face-centered cubic (FCC) phases, thus assisting the formation of FCC-Ti under elevated temperature or plastic deformation. Such a gap further decreases with the increase in the interstitial content, which is consistent with the experimental observation of FCC-Ti under high interstitial content. The relative stability of the interstitial-containing HCP-Ti and FCC-Ti was studied against the physical and chemical origins, e.g., the lattice distortion and the electronic bonding. Interstitial O, N, C and B also reduce the stacking fault energy, thus further benefiting the formation of FCC-Ti.

Solubility and mechanical properties of hydrogen / carbon in Mo–Ta alloy

The solubility, diffusivity, electronic and mechanical properties of Hydrogen (H) and Carbon(C) impurity atoms in Mo–Ta alloy were studied by first-principles calculation. The solubility energy results of C/H in Mo–Ta alloy show that H tends to form in tetrahedral interstitial site (TIS), in contrast to C which tends to octahedral interstitial site (OIS). The diffusion barrier of H/C atoms in Mo–Ta alloy was analyzed, and the results showed that Ta atom hinder the diffusion of H atom, but promote the diffusion of C atom. The electronic structure of Mo–Ta alloys was analyzed by the projected density of states (PDOS). On the other hand, the addition of C/H atoms will reduce the strength and improve the ductility of Mo–Ta alloys. For the interstitial atoms, the effect of C on the alloy is stronger than that of H due to the strong electronic interaction between C and Mo–Ta alloy. These results will help us understand the basic behavior of Mo–Ta alloy and the research of the first wall material of fusion reactor.

First-principles study of hydrogen-vacancy interactions in CoCrFeMnNi high-entropy alloy

Vacancies can easily capture H atoms in metals, forming hydrogen-vacancy complexes/clusters. In this work, the hydrogen-vacancy interactions in CoCrFeMnNi high-entropy alloy (HEA) were studied with first-principles calculations based on the density functional theory (DFT). The special quasi-random structure (SQS) method was used to construct a chemically disordered HEA, and the effects of solute H atoms on the formation energy of monovacancy, the formation energy and binding energy of multi-vacancy cluster were calculated. It is found that an H atom prefers to occupy an octahedral interstitial site neighboring a vacancy and attracts the charge from the surrounding first-nearest neighbor atoms (e.g. Co, Ni, Fe or Mn atom, excluding Cr atom), weakening the stability of the atoms around the vacancy and reducing the vacancy formation energy in CoCrFeMnNi HEA. After introducing H atoms, the formation energies of both vacancy and vacancy cluster decrease in CoCrFeMnNi HEA, but they are still higher than those in pure Fe and Ni. In addition, the reduction of the binding energy of vacancies in CoCrFeMnNi HEA is much lower than that in pure Fe and Ni, and the binding energy of vacancies even increases in some cases. The results of the first-principles calculations indicate that the solute hydrogen atoms, although promoting vacancies, unfavorably combining vacancies into clusters to form micro-voids. This provides a good explanation for the good resistance to hydrogen embrittlement of CoCrFeMnNi HEA observed in experiments.

Ab initio investigation of the screw dislocation-hydrogen interaction in bcc tungsten and iron

The interaction of hydrogen with 1/2<111> screw dislocations is investigated in body-centered cubic tungsten and iron using ab initio calculations. Different core reconstructions are evidenced, depending on the number of hydrogen atoms introduced inside the dislocation core. Corresponding interaction energies are highly attractive in both metals, with a significant contribution of zero point energy associated with H vibrations, particularly in Fe. The pinning by hydrogen of the dislocation in its reconstructed core remains efficient for a local atomic fraction of hydrogen as low as 1/5. Other octahedral interstitial sites close to the reconstructed core are also attractive, contrary to the perfect bcc crystal where these sites are unstable and where hydrogen lies in the tetrahedral sites. Hydrogen recovers its bulk behavior only beyond the eighteenth neighbor octahedral sites. A simple pair interaction model is parameterized on ab initio calculations and used with a mean-field approximation to predict the concentration profiles of hydrogen segregated in and around the dislocation core. This segregation model predicts that dislocation core-sites remain completely decorated by hydrogen atoms up to at least 750 K and 200 K in W and Fe, respectively.

Repeatable Photoinduced Insulator-to-Metal Transition in Yttrium Oxyhydride Epitaxial Thin Films

Currently, no known material retains its photoinduced metallic conductivity over a long time while also exhibiting repeatable metal-to-insulator recovery. Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YOxHy) epitaxial thin films. The temperature (T) dependence of the electrical resistivity (ρ) of the films transforms from the insulating to the metallic state (dρ/dT > 0) under ultraviolet laser illumination. The YOxHy film recovers its original insulating state when heated (125 °C) under an Ar atmosphere and regains metallic conductivity when subsequently subjected to ultraviolet laser illumination again, showing a repeatable photoinduced insulator-to-metal transition. First-principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.

First-principles calculations of transition elements interaction with hydrogen in vanadium

We performed systematic first-principles calculations to investigate the interactions of 26 transition elements (TEs) with hydrogen (H) and vacancy in vanadium (V). In the presence of 26 substitutional solute elements (Sc,Ti,Mn,Cr,Co,Fe,Cu,Ni,Y,Zr,Mo,Nb,Rh,Ru,Pd,Tc,Ag,La,Hf,W,Ta,Os,Re,Pt,Ir,Au), H still prefers to occupy the tetrahedral interstitial sites. H is unstable for solute elements at the nearest octahedral interstitial sites except for Ni and Cu. Then we calculated the binding energies of TEs and H with their distances. H atoms are attractive with early three 3d/4d/5d TEs (Sc/Ti/Y/Zr/La/Hf) and repulsive with other TEs. And we predicted the effect of solid solution elements on H diffusivity, Sc/Y/Zr/La/Hf can significantly reduce the effective diffusivity of H, while other elements have little effect on it. In addition, most of TEs can stabilize TE-vacancy-H clusters, the interactions of all TE-vacancy-H clusters are attractive and decrease with the increase of atomic number in the same period. In the case of pre-existing TE-vacancy complex defects, most of TEs can reduce the binding strength of vacancy to H. These results deepened the understanding of the TEs-H interactions and H retention in V alloys under irradiation.

Migration Barrier Estimation of Carbon in Lead for Lead–Acid Battery Applications: A Density Functional Theory Approach

Recent efforts towards developing novel lead electrodes involving carbon and lead composites have shown potential for increasing the cycle life of lead–acid (LA) batteries used to store energy in various applications. In this study, first-principles calculations are used to examine the structural stability, defect formation energy, and migration barrier of C in Pb for LA batteries. Density functional theory with the GGA-PBE functional performed the best out of various functionals used for structural stability calculations. Furthermore, with the complete incorporation of C in the Pb matrix, the results show that C is energetically preferred to be at the octahedral interstitial (CiOcta) site in the FCC structure of Pb. Additionally, climbing-image nudged elastic band calculations show a minimum energy pathway for C diffusing from a stable octahedral site to the adjacent octahedral site assisted by a tetrahedral intermediate site. Therefore, the minimum energy pathway for C migration is envisioned to be CiOcta→ CiTetra→CiOcta, where the total energy barrier is observed to be ~90% and more than 100% lower than the CiTetra→CiTetra and CiOcta→CiOcta barriers, respectively.