Tetrahedral Interstitial Sites Research Articles

Synthesis of Laves phase hydrides YFe2H6 and YFe2H7 at high pressure: Reaching a limit of interstitial hydrogen uptake

The C15 Laves phase compound YFe2 has been extensively studied for its significant hydrogen absorption in its tetrahedral interstitial sites. It can stably hold up to five hydrogen atoms per formula unit under ambient conditions. However, the maximum hydrogen capacity in such Laves phase materials remains an open question. The use of high pressure is a tool that facilitates the formation of polyhydrides with high hydrogen-to-metal ratios. By subjecting YFe2H4.2 to hydrogen pressures up to 50 GPa in a diamond anvil cell without any heating, two new interstitial compounds, YFe2H6 and YFe2H7, were synthesized. Synchrotron X-ray diffraction and ab initio calculations reveal that these new compounds have ordered hydrogen atoms occupying two types of tetrahedral interstitial sites, A2B2 and B4 (for YFe2H7), and a new triangular interstitial site AB2, in an orthorhombic structure distorted from the C15 Laves phase. The magnetic properties of YFe2Hx hydrides have to be taken into account to reproduce experimental volumes, identify stable compounds on the convex hull of the YFe2-H system, and explain deviations from Vegard’s law regarding volume expansion with hydrogen concentration. These compounds cannot be retrieved at ambient pressure upon pressure release.

Effect of Alloying on the Hydrogen Sorption in Ti–Zr–Mn-Based Alloys. Pt. 1: C14-Type Laves-Phase-Based Alloys

The alloys of the Ti–Zr–Mn system based on the C14-type Laves phase are considered as ones of the most promising materials for safe storage and transportation of hydrogen. These alloys have appropriate parameters for activating the processes of absorption and release of hydrogen, a low cost, and a fairly high cyclic stability. In this work, the microstructure and phase composition of the starting alloys and the crystal structure of the hydrides synthesized from them are studied. Possible ways to reduce the cost of the final products are shown. The fact that changing the method of the alloy fabrication does not significantly affect its hydrogen absorption properties is shown. On the example of the considered alloys, it is shown that, as expected, alloying with an element with a larger atomic radius that forms a stable chemical compound with hydrogen results in an increase in the hydrogen capacity. This is explained by both the increased radius of the tetrahedral interstitial sites, where hydrogen atoms are located after dissolution, and the higher total amount of the element interacting with hydrogen.

First‐Principle Calculation of the Hydrogen Adsorption and Diffusion Characteristics at an Ni3Al/Ni Interface

ABSTRACTThe occurrence of hydrogen embrittlement often leads to significant fracturing in materials. Thus, a comprehensive understanding of the interactions of hydrogen and its effects on material properties is essential. In this study, first‐principle calculations based on density functional theory are conducted to investigate the adsorption and diffusion characteristics of hydrogen at the Ni/Ni3Al(γ/γ') interface of a Ni‐based single‐crystal superalloy. The results show that hydrogen can stably adsorb onto the γ/γ′ interface, nearby octahedral interstitial sites, and tetrahedral interstitial sites in the γ‐phase. Analysis of the density of states and charge density confirms that the hydrogen atoms formed covalent bonds and ionic bonds with nearby Al atoms. A transition state structure search based on linear synchronous transit (LST) and quadratic synchronous transit (QST) models is utilized to calculate the diffusion paths and energy barriers of the hydrogen atoms between the stable adsorption sites near the interface. In addition, the permeation characteristics of hydrogen atoms at the interface are analyzed. Furthermore, it is confirmed that hydrogen atoms entering the matrix from the interface preferentially occupy the positions of the regular octahedral interstitial sites, diffuse towards adjacent regular 6Ni octahedral interstitial sites through the inclined octahedral interstitial sites between the atomic layers, and converge at the interface.

Unraveling the delithiation mechanism of air-stabilized fluorinated lithium iron oxide pre-lithiation material

Integrating pre-lithiation materials into the cathode to compensate for the irreversible loss of active lithium ions due to the anodes is one of the essential technologies for achieving high-energy lithium-ion batteries. Li5FeO4 (LFO) has emerged as an appealing candidate for its high initial charge specific capacity, cost-effective, and suitability for the solvents/binders. Unfortunately, suffering from notorious degradation while in storage hinders its large-scale application. Furthermore, the delithiation mechanism and the impacts of oxygen species during charging remain elusive. Herein, a fluorinated LFO, featuring the F-doped carbon layer on the surface and gradient fluorination in the bulk, is synthesized to overcome the above obstacles. Surface modification enhances the air stability in storage and prevents oxygen species from attacking the electrolyte upon charging. The introduction of fluorine is proposed to lower the migration barrier of Fe from the tetrahedral interstitial site to the octahedral one and narrow the band gap, thus maintaining a stable phase transition at high charge density. As a result, the fluorinated LFO possesses excellent air stability (541.9 mAh g−1 after humid air exposure of 24H) and exhibits attractive initial charge specific capacity (703.4/580.5 mAh g−1 at 0.05/1.0C rate) as well as slight electrolyte decomposition during the charging process. This work opens up an alternative avenue to developing industry-applicable pre-lithiation materials for high-energy batteries.

Origin of the metamagnetic transitions in Y0.9Tb0.1Fe2D4.3

Deuterium insertion was used to tune the magnetic properties of Y0.9Tb0.1Fe2 Laves phase towards an itinerant electron metamagnetic (IEM) behavior. The latter is highly sensitive to chemical changes and external parameters. The structural and magnetic properties of Y0.9Tb0.1Fe2D4.3 were investigated using various neutron powder diffraction experiments in addition to magnetic measurements under steady and pulsed high magnetic fields up to 60 T. The deuteride crystallizes in a monoclinic structure (Pc space group) with 4.3 D atoms located in 18 tetrahedral interstitial sites. At zero field, it undergoes a ferrimagnetic-antiferromagnetic (FiM-AFM) transition at TM0 = 90 K, accompanied by an anisotropic magnetostriction and a negative cell volume expansion of 0.6 %. A second AFM-PM transition is observed at 146 K. Under pulsed magnetic field at 4.2 K, the deuteride displays a multistep magnetic behavior from ferrimagnetic to a ferromagnetic state, which can be attributed to a stepwise rotation of the Tb moments. The ZFC-FC magnetization curves at low fields exhibit an irreversibility below 90 K, followed by a sharp decrease in magnetization at the FM-AFM transition. Between 90 K and 130 K, the magnetization curves display an IEM behavior, with the transition field increasing linearly with temperature.

Incorporation and substitution of ions and H2O in the structure of beryl

Abstract. Incorporation of ions into the crystal structure of beryl (Be3Al2[Si6O18]) can take place by direct ion-to-ion substitution of the framework components Al3+, Be2+ and Si4+ or by occupation of interstitial or structural channel sites. The most common impurities in beryl include transition metals, alkalis and H2O. It is accepted that the transition metals Mn, Cr and V directly substitute for Al at the octahedral site and induce colour. Similarly, the octahedral site can host Fe instead of Al. Nevertheless, it is shown that it remains disputed whether Fe can also be present at the tetrahedral, interstitial, or channel sites, and opposing hypotheses exist regarding these possibilities. However, in the case of Fe, not only the possible occupation of these sites remains under debate, but also their influence on the subsequent colour of beryl. Similarly, the residence of Li in the channels and at the Be tetrahedral or interstitial tetrahedral sites is still under debate. The presence of more than two types of H2O (type I and type II) in the structural channels of beryl is also unclear. This article aims to give an overview on the consensus and on the current debates found in the literature regarding these aspects. It mainly concentrates on the substitution by and the role of Fe ions and on channel occupancy by H2O.

Prior implantation of hydrogen as a mechanism to delay helium bubbles, blistering, and exfoliation in titanium

This study explores the delaying of the formation of helium bubbles and blisters in pure titanium by hydrogen pre-implantation. Titanium, implanted with helium (40 KeV, 5 × 1017 ions/cm²), exhibited large bubbles that cause exfoliation after heat treatment, whereas hydrogen pre-implantation inhibited bubble growth at room temperature and reduced the exfoliation after heat treatment.In the samples pre-implanted with hydrogen, we found evidence of helium diffusion delay by: (a) a fourfold reduction in bubble pressure (b) faceted cavities in the samples (c) a smaller increase in titanium lattice parameters (d) a 16-fold reduction in average bubble size and a sixfold reduction in bubble area fraction (e) a more than twofold decrease in exfoliation (f) a tendency toward the formation of larger bubbles as a result of heat treatment. We believe that it is reasonable to assume that the inhibition of helium diffusion between tetrahedral interstitial lattice sites takes place because of the occupation of the intermediate octahedral sites by hydrogen atoms.Evidence for the opposite effect, that is inhibition of the diffusion of hydrogen in the presence of helium, is found in the retention of hydrogen in the specimens at elevated temperatures. This retention allowed the existence of titanium hydride after heat treatment at 680 °C. The present study sheds light on the intricate interplay between hydrogen and helium in titanium, providing insights into mechanisms that can potentially mitigate helium-induced damage in materials.

Exploring the impacts of Li and He impurities in a tungsten matrix: A First-Principles study

The liquid Li coating on the plasma-facingmaterials (PFM) has been suggested and implemented as a viable and efficient solution to overcome the damage of plasma on PFM in Tokamak devices. However, the internal mechanisms and impacts of tungsten-based PFM are not yet fully understood. Here, we demonstrate the effects of the impurities with multiple Li atoms, the co-doped Li and He atoms, and the self-trapping induced by the He8/He12 and LiHe8/LiHe12 clusters on the mechanical properties and melting point of W, with the aid of the optimized structures, the formation energies, the charge density distribution, and the density of states obtained by the first-principles calculations. The bulk, shear, and Young moduli, together with the anisotropy factor and Poisson ratio, are calculated for each structure by using the calculated elastic coefficients to understand the effects of impurities on the mechanical properties of W. The results show that the substitutional site in the W matrix is more likely to be occupied by a single Li impurity atom and the impurity He atoms prefer the octahedral interstitial, at the same time, the additional Li impurity atoms are more likely to be located at tetrahedral interstitial sites. The charge density distributions and density of states exhibit that the bond energies involving the highly doped Li or He atoms decrease, which leads to a substantial decrease of elastic coefficients and then obviously reduces the melting points, and the shear and Young moduli, although the impurity of single Li and the self-trapping of the single He8/He12/LiHe8/LiHe12 clusters can maintain these physical quantities as PFM. It implies that the impurity concentration of Li or Li-He in the W matrix should be strictly controlled in the PFM application. Therefore, the present investigations can provide a helpful guide for developing PFM with tungsten.

Density functional study on the mechanics, thermodynamics, and H diffusion mechanism of LiH

LiH is valued by researchers and engineers for its high-temperature resistance, high strength, high hydrogen storage capacity of up to 12.6 wt%, and high neutron absorption cross section. However, sintering and application of this material are difficult. Lithium hydride is a highly effective neutron shielding material. The neutron shielding ability of lithium hydride is directly affected by the homogeneity of the total amount and distribution of hydrogen. The heat migration of hydrogen reduces the neutron shielding effectiveness of lithium hydride. It is critical to forecast H's diffusion behavior. The diffusion coefficient is a critical metric for determining the diffusion efficiency. As a result, the stability, electronic structure, and bonding properties of LiH, LiOH, and H entering the tetrahedral interstitial sites of LiH were calculated using first principles based on density functional theory (DFT). The elastic modulus of the system was also examined to find the lowest thermal conductivity, and some thermodynamic parameters were derived by calculating LiH phonons. Finally, static calculations were used to determine the diffusion coefficient and diffusion activation energy of H in the LiH solid solution. The results revealed that the addition of H altered the characteristics of the LiH semiconductor, giving it metallic features. The lowest thermal conductivity of the LiH system was 2.9. W·m−1 K−1. The diffusion coefficient was D=(2.638×10−2cm2/s)exp(−5.811×10−3cal/KBT). The activation energy for diffusion was 0.252 eV. The diffusion coefficients, elastic constants, and lattice parameters all corresponded well with previously published results. The density functional theory was employed to study the material's system energy and electrical structure, and the microscopic migratory behavior of hydrogen was predicted theoretically. The calculation of the lowest thermal conductivity provided a reference for the screening of ceramic materials.

Promoting reversibility of layered potassium cathode through interstitial doping

With the increasing needs for large-scale and low-cost energy storage devices, Mn-based layered oxide cathodes have achieved considerable researching interests for potassium-ion batteries owing to their high energy density, abundant resource and low toxicity. However, their developments are challenged by the absence of suitable cathode materials to tolerate large-sized K-ion insertion/extraction and the presence of Jahn-Teller distortion of Mn3+. To address this issue, we present a strategy of embedding boron into interstitial tetrahedral sites to obtain a P3-K0.5Mn0.8Co0.2B0.1O2 cathode. Strong B-O covalent bonds facilitate the construction of robust orthorhombic framework and alleviate the undesired elongation of Mn-O bonds, contributing to excellent electrochemical performance. In addition, boron ions are verified to promote the formation of a homogeneous cathode electrolyte interphase layer, improving interfacial stability and realizing highly reversible cycling in a wide voltage range (1.4–4.3 V). This strategy provides a new pathway towards the development of high-performance cathode materials for potassium-ion batteries.

Exploring solute-defect interactions in nanosized palladium hydrides across multiple time scales

We employ two different atomistic methods to investigate solute-defect interactions in nanosized palladium–hydrogen (Pd–H) systems across multiple time scales. The first method, referred to as Diffusive Molecular Dynamics (DMD), focuses on capturing hydride phase transformation and the evolution of solute-induced lattice defects over a diffusive time scale. The second method, Molecular Dynamics (MD), provides more detailed insights into atomic movements and lattice relaxation over the time scale of thermal vibrations. These two methods are connected with MD simulations initialized using statistical measures of microscopic variables obtained from DMD at different H/Pd ratios. Our study demonstrates that DMD effectively captures the propagation of an atomistically sharp hydride phase boundary as well as the dynamics of solute-induced misfit dislocations and stacking faults. While the H-concentrated phase leads to a reduction in the vibrational energy, the presence of stacking faults locally increases the vibrational energy of both Pd and H atoms. Furthermore, the MD simulation results align with DMD in terms of equilibrium potential energy, the preservation of hydride phase boundary, and the spatial distribution of stacking faults. We thoroughly characterize the lattice crystalline structures in four key regions of the particle. We observe a preference for H atoms to occupy tetrahedral interstitial sites near stacking faults due to the lower stacking fault energies provided by these sites within the H-concentrated phase.

First-principles study of hydrogen capture, solution and mechanical effects in transition metal tungsten alloy W-TM (V, Nb, Ta)

Tungsten alloy as a candidate for plasma facing materials (PFMs) in thermonuclear fusion experimental reactor (Tokamak) is of great significance for the successful use of nuclear fusion. Therefore, it is worth exploring to understand the problems of solution and retention of hydrogen (H) and its isotopes in transition metal (TM) and tungsten (W) forming isotype alloys. Based on density functional theory, the effects of hydrogen solution in W-TM (TM = V, Nb, Ta) alloy on energetics, bond length, electronic structure and mechanical properties are studied by first-principles calculations. The calculated solution energy indicates that a single H atom is more easily trapped by tetrahedral interstitial sites in the W-TM alloy, and WV alloy has the strongest trapping ability for single H atoms and the strongest interaction between them. With the increase of H impurity atoms, H is more likely to form aggregation in W-TM. The accumulation of multiple hydrogen impurities will cause serious fluctuations in the mechanical properties and melting point of W-TM alloy, among which WV alloy is least affected by H accumulation and has a strong ability to resist the effect of H accumulation. The results can provide a reference for understanding the behavior of H in the plasma facing material.

Near Room-Temperature Intrinsic Exchange Bias in an Fe Intercalated ZrSe2 Spin Glass.

Some magnetic systems display a shift in the center of their magnetic hysteresis loop away from zero field, a phenomenon termed exchange bias. Despite the extensive use of the exchange bias effect, particularly in magnetic multilayers, for the design of spin-based memory/electronics devices, a comprehensive mechanistic understanding of this effect remains a longstanding problem. Recent work has shown that disorder-induced spin frustration might play a key role in exchange bias, suggesting new materials design approaches for spin-based electronic devices that harness this effect. Here, we design a spin glass with strong spin frustration induced by magnetic disorder by exploiting the distinctive structure of Fe intercalated ZrSe2, where Fe(II) centers are shown to occupy both octahedral and tetrahedral interstitial sites and to distribute between ZrSe2 layers without long-range structural order. Notably, we observe behavior consistent with a magnetically frustrated and multidegenerate ground state in these Fe0.17ZrSe2 single crystals, which persists above room temperature. Moreover, this magnetic frustration leads to a robust and tunable exchange bias up to 250 K. These results not only offer important insights into the effects of magnetic disorder and frustration in magnetic materials generally, but also highlight as design strategy the idea that a large exchange bias can arise from an inhomogeneous microscopic environment without discernible long-range magnetic order. In addition, these results show that intercalated TMDs like Fe0.17ZrSe2 hold potential for spintronic technologies that can achieve room temperature applications.

A DFT Approach and Perspective of Sodiation in Ag2O Host: Exploration towards Sodium Batteries

Inspired by the high volumetric energy density and biocompatibility of Ag2O, the exploration of sodiation mechanism with one and two Na atom(s) per Ag2O unit cell has been carried out. Here, Na adsorbed at tetrahedral interstitial site (TIS) of Ag2O emerges to be the most stable with energy of –6.98 eV leading to the formation of Na–Ag2O compound. The advancement of Ag2O towards a metallic state is evidenced by the absence of a forbidden energy gap in the band structure plot with Na inclusion. Also, the formed compound is confirmed from PDOS plots and by analysing the charges transferred between Na, Ag and O atoms from CDDP. Further, when the concentration of Na is stepped up to two, the most stable TIS and Agsub sites exhibits an energy of –5.79 eV Na−1 atom. In this case, the Bader charge analysis reveals that Na prefers to form strong contacts with Ag and weak interactions with O, thus demonstrating the feasibility of alloying rather than the conversion product. Subsequently, NEB studies show that the surface diffusion of Na from one TIS to the adjacent unit requires a minimal activation energy thereby suggesting the suitability of Ag2O as an alloying host.

Non-Stoichiometric <i>fcc</i>-Base GdO<i><sub>x</sub></i> Precipitations in a Mg–Zn–Gd Alloy

We have found that, during in-situ scanning transmission electron microscopy observations, heating of a Mg97Zn1Gd2 (at.%) alloy at 623K leads to dynamic precipitations of face-centered-cubic (fcc)-based Gd nanoparticles. With the aid of density-functional theory (DFT) calculations, the observed lattice constant of 5.32 Å, which is larger than that expected for pure fcc-Gd of 5.06 Å, is likely to be due to oxygen atoms inserted at tetrahedral interstitial sites with essentially a fractional occupation. Systematic DFT calculations show that the fcc-base GdOx can be stable configurations in a wide composition range, where the O atoms behave like a solute up to x ~ 1.5 to provide continuously the non-stoichiometric GdOx solid-solution phase.

Anion-Cation Dual-Ion Multisite Doping Stabilizes the Crystal Structure of Li-Rich Layered Oxides.

Li-rich layered oxide (LLOs) cathode materials are gaining increasing attention as lithium-ion batteries (LIBs) pursue greater energy density. However, LLOs still suffer from severe capacity fading and voltage decay due to their unstable crystal structure. Hence, the anion-cation dual-ion multisite doping strategy based on Mg and S atoms is used to stabilize the crystal structures of LLOs. Mg substitutes Li atoms in the Li and transition-metal (TM) layers, while S atoms occupy tetrahedral interstitial sites and lattice O sites, all of which contribute to the crystal structure stability of LLOs. Theoretical calculations show that Mg/S dual-ion multisite doping successfully reduces the energy levels of the TM 3d-O 2p and isolated O 2p orbitals, which effectively stabilizes the lattice oxygen. Therefore, multisite-doped samples exhibit promising electrochemical performance. This strategy provides a new approach to enhance the crystal structure stability of LLOs for the design of high-energy-density Li-ion batteries.

Modification mechanism of Ti-6Al-4V alloy with pre-coated Ti-Cu-Al multilayer film treated by ion nitriding: Experiments and first-principles calculations

In this paper, the Ti-6Al-4V(TC4) alloy specimens pre-coated with Ti-Cu-Al multilayer films were plasma nitrided at different temperatures (673K-823K), and their microstructure and mechanical properties were studied. Surface hardness changes induced by pre-coating combined with plasma nitriding were also analyzed and correlated with microstructural features and elemental distribution. Ti-Cu-Al multilayer films with clear interfaces on deformed TC4 alloy were fabricated. The multilayer structure survived after nitriding, and a thick gradient nitrided layer with a gradient distribution of N elements was formed. The bonded nitride on the surface provides high hardness, reaching 948HV at 723K. In addition, the nitride TC4 alloy's wear resistance exhibits a significant improvement compared with the untreated specimen, especially at 823K, the mass wear rate decreased by more than 80%. It is mainly attributed to the N/metal element gradient distribution of the thick nitride layer. The nitriding behavior of α-Ti/Cu/Al was investigated by first-principles calculations. According to the thermodynamic calculation results, N atoms preferentially occupy the octahedral interstitial sites of α-Ti and the tetrahedral interstitial sites of Al. It is worth noting that N atoms have poor thermodynamic stability in Cu, which is consistent with the experimental results. The calculated elastic properties agree with the experimental cross-sectional hardness results, showing a smooth decreasing trend of the complex modulus and hardness on the micrometer length scale and explaining the improved structure performance. These results may provide crucial inspirations for future experimental work preparing high-performance nitrided layers.

Hydrogen Solution in Tetrahedral Interstitial Sites in ZrCo Hydrides: A First-Principles Study

This work aims to investigate the characteristics of the H atom in the tetrahedral interstitial sites of 8f2, 4c1, 8f1, 4c2, 8e, and 8g1 in the ZrCoH3 cell by first principles calculation based on the density functional theory. The research shows that pressure can change the local property of the electrons and the bonding ability of the H atom and its adjacent metal atoms, resulting in changes in the stable point and the disproportion point of the H atom in ZrCoH3. Further research has found that at P = 0 GPa, the significant Co-H covalent bond makes the H atom prefer to occupy the tetrahedral interstitial sites of 8f1 and 4c2 in the ZrCoH3 cell, while the H atom occupying the tetrahedral interstitial site of 4c1 in the ZrCoH3 cell has a significant Zr-H ionic bond with its adjacent Zr atom, which is the reason for the disproportionation of the ZrCoH3 alloy. When P = 10 GPa, the H atoms become unstable in the 8f1 and 4c2 tetrahedral interstices of the ZrCoH3 crystal cell. The significant Zr-H ionic bond between the H atoms in the 8f1 tetrahedral interstice and their adjacent Zr atoms is the reason for the disproportionation of the ZrCoH3 alloy, and the significant Co-H covalent bond makes the H atoms preferentially occupy the 4c1 and 8g1 tetrahedral interstices.

Structure and stability investigation of oxygen interaction with Fe in bcc-Fe

The precise interaction mechanisms between body-centered cubic Fe and the unavoidable interstitial O atom are critical to understanding oxidation resistance. Even though the Fe–O interaction has been investigated extensively for centuries, the physical evolution processing including the stability, bonding characteristics, and magnetism, remains as one of the most important scientific issues. Here, a four-level (atomic, electronic, orbital, and spin-level) analysis was employed to investigate the precise interactions between Fe and O atoms by multiple complementarity methods (Madelung energy calculation, electronic density analysis, crystal orbital Hamilton population analysis and topology analysis of spin maps). The stability of Fe atoms was enhanced with the O atom at the tetrahedral interstitial site. The bonding strength between Fe and O atoms originates substantially from s orbits. Furthermore, the topology of the minority-spin was changed by the magnetic moment flip of O, and the interaction among Fe atoms were strengthened. A further understanding of the Fe–O mechanism provides a theoretical basis for obtaining excellent physical properties in Fe-based materials.

Dislocation-twin interaction in medium entropy alloy containing a high density of oxygen interstitials

Dislocation-twin interactions play important roles in tuning the plastic deformation of materials. Here, we report the great influence of interstitial oxygen atoms on dislocation-twin interactions in NiCoCrO medium entropy alloy through in-situ transmission electron microscopy mechanical testing, atomic resolution energy-dispersive X-ray spectroscopy characterizations, and integrated differential phase-contrast scanning transmission electron microscopy imaging. The spreading lattice distortion in medium-entropy alloy was found to enable large oxygen interstitial solubility. Oxygen atoms occupied both the tetrahedral and octahedral interstitial sites, and tended to be enriched at defects such as twin boundaries and stacking faults. Oxygen-enriched regions near the twin boundary hindered dislocations from direct transmitting or cross-slip into another twin plane during plastic deformation, resulting in significant dislocation entanglement, partial dissociation of dislocations, and the deviation of slip directions. Our results give insight into the strengthening mechanisms associated with the synergetic effects of twin boundary and interstitial atoms.