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CrMoV steel was exposed to 500, 550, and 600 °C for up to 120 h in 0.1 and 10 MPa CO2. A significant change in carbon deposition content was not observed in the 0.1 MPa CO2, in contrast to the high carbon content at 550 °C and 10 MPa CO2. The formation of internal Fe-rich M3C carbides and super saturation of steel grains with dissolves carbon at 550 °C but not at 500 and 600 °C may be responsible for this difference. The effect of carbon deposition on the outward Fe diffusion via vacancy or interstitial sites was also discussed.

We report two new quaternary BaCu6Sn2As4−x and BaCu6Sn2P4−x phases with a new structure type, which are fully characterized by single crystal X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These two phases crystallize in tetragonal cell with space group I4/mmm (#139) and Pearson symbol tI26. The refined lattice parameters are a = 4.164(1) A, c = 24.088(3) A for BaCu6Sn2As4−x, and a = 4.053(2) A, c = 24.08(1) A for BaCu6Sn2P4−x, respectively. They possess a distinct layered feature composed of Cu6Sn2Pnx (Pn = P, As) layers sandwiched by the Ba atoms. The Cu-Sn framework of the Cu6Sn2Pnx layer is closely related to the well-known Cu2Sb-type structure, and Pn atoms are found occupying two interstitial sites caused by close packing of Cu and Sn atoms or capped on the top of square nets formed by Cu atoms. The compounds are also characterized by electrical transport measurements down to 2 K.

In general, thermal treatment of W produces non-stoichiometric tungsten oxides under suitably reducing atmosphere. Anomalously, the present work reports the cubic-H0.5WO3 by heat treatment of nanocrystalline W under H2O(v) atmosphere. The nanocrystalline W readily oxidizes at lower temperatures due to its enhanced oxidation kinetics compared to the as-received form. The W reacts with H2O(v), which forms γ-WO3 along with hydrogen as a byproduct. Followingly, the H intercalation to the interstitial sites of WO3 results in nanocrystalline cubic-H0.5WO3. The crystallographic relationship of this formation pathway follows (110)W//(010)WO3//(010)H0.5WO3. As per the unit cell volumes of WO3 and H0.5WO3, a single unit cell of WO3 turns into 8 unit cells of H0.5WO3 with H atom intercalation.

Intermetallic metal hydrides are critical materials for hydrogen storage applications, however, metal hydrides with greater storage capacities are still needed. Within metal hydrides, the volumetric storage capacities are limited by the number of hydrogen-accommodating interstitial sites which can be simultaneously occupied given a minimum hydride nearest-neighbor distance of ≈ 2.1 A, according to the Switendick-Westlake criterion. To date, violations of this criterion are rare. Perhaps the most well studied compounds violating this criterion are the RNiInHx compounds (R = Ce, La, Nd). Previous neutron diffraction studies on the deuterated species revealed the presence of Ni–D∙∙∙D–Ni–D∙∙∙D–Ni chains with anomalously close D∙∙∙D contacts of ≈ 1.6 A. Yet there are no neutron vibrational spectroscopic investigations reported for these atypical hydrides. Here we use neutron vibrational spectroscopy (NVS) measurements to probe the hydrogen dynamics in LaNiInHx (x = 0.67, 1.6) and CeNiInH1.4. For x > 0.67, the presence of close H∙∙∙H contacts yields two related features in the vibrational spectrum centered near ≈ 90 meV corresponding to the oscillations of paired H atoms simultaneously occupying neighboring R3Ni tetrahedra. Notably, these features are energetically distinct from comparable vibrational motions for “unpaired” H atoms when x ≤ 0.67. To compare, we also present powder neutron diffraction and NVS measurements for the newly characterized, chemically similar Sn compounds CeNiSnH, CeNiSnH2, and CeNiSnD2. These compounds also contain R3Ni tetrahedra, however, the H-occupied tetrahedra are well separated from each other with the closest H∙∙∙H distances exceeding 2.1 A, and the Switendick-Westlake criterion is not violated. Consequently, the spectral signature of the close H∙∙∙H contacts is absent in these hydrides.

This work reexamines the insertion of O atoms in the L1 0 γ -TiAl system using first-principles calculations and thermodynamic modeling in the independent point defect approximation. It includes a study of intrinsic point defects, the insertion of many alloying elements (more than twenty were considered), as well as a study of their interaction with oxygen. The formation of complex defects composed of either vacancies, anti-sites or solute elements is then studied. Results at the atomic scale show a high segregation of oxygen in titanium-rich environments: oxygen easily segregates onto Ti anti-sites ( Ti Al ) and alloying elements are located in the vicinity of Al sub-lattices. DFT point-defect energetics shows that there is a clear correlation between the nature and site preference of an alloying element, and the oxygen segregation energy in the vicinity of this solute. The thermodynamic model shows that at equilibrium, oxygen does not occupy isolated interstitial sites but prefers to be located in the vicinity of Ti anti-sites or alloying elements. The effect of this strong segregation on oxygen diffusivity is discussed hereinafter. Results show a strong slowdown in oxygen diffusivity due to intrinsic defects. For Ti/Al > 0 . 5 ratios, the traps for O diffusion are mainly constituted by Ti anti-sites, and the addition of solutes does not contribute much to the trapping of diffusing O atoms. For Ti/Al 0.5 ratios however, the contribution of solutes to trapping phenomena can be very important, and a decrease by 1–2 orders of magnitude of effective O diffusion coefficients can be observed for temperatures around 800–1100 K.

The present study deals with site occupancy of cobalt in Ni–Zn ferrite investigated by in-field Mossbauer spectroscopy at 300 K, 77 K, and 5 K coupled with X-ray diffraction, Fourier transform infrared spectroscopy, and Rietveld analysis. The cation distribution for the whole series of compositions was proposed by consideration of the amounts of iron ions present at tetrahedral and octahedral interstitial sites. Confirmation of the proposed distributions was achieved by quantitative estimation of the lattice constants for these compositions and comparison with experimental values. Pauling electronegativities remain almost constant, indicating no significant variation in the strength of the ionic bond with cobalt substitution. The observed decrease in the Debye temperature calculated with both the Waldron formula and the Anderson formula suggests that as a result of cobalt doping, there is slight enhancement in lattice vibrations, which is attributed to the minor weakening of the interatomic bonding between the atoms in the spinel lattice.

Spinel LiNi0.5Mn1.5O4 (LNMO) is widely utilized because of its high-energy-density and high-voltage. Unfortunately, there is still much research to be done for LNMO due to its poor structural stability. Here, a strategy is confirmed to stabilize LNMO via modulating interstitial sites. The interstitial 16c sites of the octahedron are partially occupied by Ni2+ to suppress the migration and dissolution of manganese ions upon electrochemical cycling and stabilize lithium-ion vacancies in the state of charge. Unexpectedly, this protocol not only suppresses the phase separation restraining the phase boundary dislocations and stress but also decreases the magnitude of cell volume change during cycling, which originates from the change in Ni redox couple energy states. This two-pronged modification strategy endows the cathode material with a lower charge transfer barrier and faster Li+ transfer kinetics, revealing superior electrochemical performance. The regulated cathode material remains robust after 900 cycles at 1 C and its capacity retention rate is 29% higher than that of the original sample. Our research is useful for providing a concrete example of how the electrochemical performance of spinel LNMO and other high voltage cathode materials can be enhanced.

Metal cation doping is an established strategy to increase the efficiency of perovskite solar cells. However, the underlying mechanism is less discussed regarding the doping site. In this paper, the effect of rubidium/potassium as dopant has been evaluated on the CH3NH3PbI3 (MAPbI3) perovskite lattice. At the 5% doping level, K cations have significantly improved photovoltaic properties by promoting crystallinity, releasing the strain, reducing the trap states, and boosting all key photovoltaic parameters. Moreover, this study provides a rough description of Rb/K doping mechanisms in the MAPbI3 lattice, where K cations occupy the interstitial sites while both interstitial and substitutional occupancies may occur for Rb cations. Our findings help to adjust the properties of perovskite layers to design new materials with better photovoltaic performance.

The generalized gradient approximation within density functional theory is used to calculate the total energies of Ag doped As2S3 configurations. The Ag is doped at octahedral, tetrahedral, c face centre and cell corner interstitial sites and As and S substitutional sites. It is found that with Ag at c face centre Ag0.25As2S3 configuration is most stable. The band structure, density of states and optical properties are investigated for this configuration. It is found that donor states are introduced below the EF in the gap region which leads to n type conductivity. The calculated values of refractive index, optical conductivity and absorption coefficient are more close to the available experimental data than those for substitutional configurations. Therefore Ag doped in As2S3 at low concentrations of Ag may occupy the c face centre interstitial site rather than any substituitional site.

The hydrogen sorption properties of Ti4M2Oy compounds (M = Fe, Co, Ni, Cu or their mixture and y = 0, 1) were studied to assess their utility as room-temperature hydrogen storage materials. The main parameter controlling the hydrogen sorption property is the energy of hydrogen incorporation into the compounds, which was evaluated by density functional theory total-energy calculations. Energetics provides basic information on the sequence of hydrogen filling into the available interstitial sites, and when the minimum H–H distance is also considered, a more sensible prediction of the site occupation becomes possible. The calculation results suggested that between Ti4Fe2O and Ti4Ni2O, Ti4Ni2O was a better candidate for room-temperature hydrogen storage. An almost-single-phase Ti4Ni2O compound was successfully synthesized starting from TiO2, Ti, and Ni using the arc-melting method. Ti4Ni2O stored 1.3 wt% of hydrogen under 7 MPa of H2 pressure at 30 °C. The storage properties of Ti4Ni2O were modified by the partial substitution of Fe, Co, and Cu for Ni. The partial substitution did not improve the usable capacity, but the hydrogen absorption–desorption characteristics demonstrated that the equilibrium hydrogen pressure could be precisely controlled via composition change.

Here, we examine the intrinsic ion conduction properties of Li7P3S11-type materials, one of the important solid electrolytes for lithium batteries, through a comprehensive computational investigation on the interplay among the crystal structure, defects, and diffusion mechanism. Our extensive ab initio molecular dynamics calculations suggest that the Li7P3S11 crystal frame is inherently flexible with readily-fluctuating P2S7 polyhedra and possesses high density of interstitial sites, which flatten the overall energy landscape for ion migration and provide higher degrees of freedom for ion movement. Statistical analysis also presents that ionic conduction in Li7P3S11 is negligibly influenced by the presence of defects and the change of charge carrier concentrations. It implies that the intrinsic high ionic conductivity of Li7P3S11 can be easily preserved in various chemical conditions during the synthesis or electrochemical operations under Li-rich or vacancy-rich conditions. This study broadens our unders...

The geometry optimization of the nitrogen-doped diamond has been carried out by the density functional theory (DFT) calculations. We model the defective diamond of substitutional and interstitial nitrogen atoms by using a simple-cubic supercell. Atoms in the supercell are relaxed by allowing them to move so that the atomic forces are less than 5.0 × 10-3 eV/Å. We calculate the formation energy for substitutional and interstitial sites. We find that the formation energy for the substitutional defect is10.89 eV. We check the convergence of the calculation with respect to the k×k×k - Monkhorst-Pack grids. We show that the energy difference between k = 4 and 6 is very small (7.0 meV). We also check the calculations by using a 216-sites supercell and find that the energy difference is 0.10 eV. Thus, the calculations of the formation energy converge well. As for the interstitial defect, we model some possible configurations and find that the smallest formation energy is 21.88 eV. Therefore, the most stable configuration of the nitrogen-doped diamond belongs to the substitutional site.

—The Cu2 – xSe (0.03 ≤ x ≤ 0.23) powders fabricated by mechanochemical synthesis have been studied by X-ray diffraction. The in situ study has been carried out for the temperature dependences of the lattice parameters, the structures, and the phase compositions of the powders in the temperature range 25–350°C. The powder compositions are shown to differ from the charge compositions and are shifted to lower copper concentrations. The estimation of peak half-widths of the cubic β phase indicates an increase in the structure imperfection after the phase transition from the α phase to the β phase of Cu2 – xSe at ~140°C. It is shown that the superpositions of the subtraction solutions (copper vacancies) and interstitials solutions (copper atoms in interstitial sites), whose proportion is changed as a function of temperature and the deviation from stoichiometry, are in the thermodynamic equilibrium in the copper selenide solid solution at room temperature. The change in the slope of the dependence of the lattice parameter of the powder Cu2 – xSe samples on the composition (0.03 ≤ x ≤ 0.23) in the temperature range 25–350°C enables the suggestion that interstitial copper atom concentration increases with temperature and deviation from stoichiometry.

Films of SiO2 spheres in a periodic array infiltrated with Au nanoparticles (NPs), were obtained by the co-assembly method. Samples with low (M1), medium (M2) and high (M3) concentrations of Au NPs were characterized by SEM, TEM and UV-Vis and Raman Spectroscopies. The images from the microscope show that the average size is 275 nm and 22 nm for SiO2 sphere and Au NP, respectively. Also, with the infiltration procedure the NPs form clusters and reside in the interstitial sites of the FCC array without modifying significantly the distance between the centers of the SiO2 spheres. However, the photonic band gap is shifted to larger wavelengths compared to the bare SiO2 Film. These samples are proposed as SERS substrates, and to evidence their sensitivity, Methylene Blue was used as the molecular probe at different concentrations. An Enhancement Factor, EF, of ∼ 10 5 is reached when the M3 film is used as SERS substrate. To have an insight about the Au NPs concentration effect in the SERS EF, discrete dipole approximation was employed to calculate the near electric field intensity of a system of SiO2 spheres and Au NPs, observing that the near field is more intense in the region between the SiO2 sphere surface and the Au NPs close to it.

Deposition of an interstitial atom in octahedral or tetrahedral sites in a bcc-crystal provokes one of three types of local tensorial eigenstrains. Interaction of the interstitial atoms with an external and/or defect-generated stress state and their diffusion cause different occupancies of individual types of sites. The diffusion paths are analyzed for atoms occupying octahedral or tetrahedral sites. The current original model quantifies the anisotropy of diffusion by factors being functions of occupancies of individual types of sites. Coupling of this new model with a very recent model of interstitial diffusion, already accounting for various types of interstitial sites, provides a rather sophisticated theoretical model for simulation of interstitial diffusion in stressed crystals.

Experiments on investigating the thermodynamics properties of palladium hydride after aging as palladium tritide with different storage periods upto 6.5 years have been performed. By analyzing the experimental results, it is found that during the formation and the decomposition of palladium hydride the entropy changes maintain a linear relationship with the helium content in solid, whereas the enthalpy changes keep constant. The sum of interstitial sites in the host palladium matrix is expected to be affected by helium, resulting in the modification on the entropy changes.

Prepared by the precursor method, lithium-doped cadmium oxide samples were synthesized using mixed formates of Cd 1- x Li x (HCOO) 2 ·2H 2 O (0 ≤ x ≤ 0.075) as a precursor. NMR spectra were obtained on the lithium nuclei incorporated in cadmium oxide; and it is demonstrated that there is only one type of impurity centers to be found. The first-principle method using a projector augmented wave (PAW) approach is applied to carry out electronic band structure calculations and to analyze optical absorption spectra for the cases of lithium atoms occupying interstitial sites and of lithium atoms substituting for cadmium or oxygen atoms. Calculations are carried out to determine energy-efficient preferences for sites of impurity centers, which indicate as the most probable the presence of lithium atoms at the interstitial sites, with vacancies observed in the cadmium sublattice. The presence of lithium atoms at the interstitial sites appears to be explaining the conductivity increase and the red-shift of the absorption edge observed in experiments.

The lack of understanding in engineering cation defects in metal oxides has impeded the development of high performance, and transparent electronic devices. Through studying the formation energy of various cationic defects in Mn-doped SnO2 via simulation, we found Mn3+ cations occupy the interstitial sites of SnO2 nanocrystals, and we proved that such defects can be engineered to significantly improve resistive switching performance of tin oxide-based devices. With this finding, a new solution-processed approach has been developed to synthesize Mn-doped SnO2 nanocrystals with a self-assembly technique for high quality transparent Mn-doped SnO2 thin film fabrication. Defect migration behavior of the Mn-doped SnO2 thin film was studied by building a metal-oxide-metal sandwich device. The effects of cationic defects, such as Mn interstitials, on the charge transport behavior were further studied to reveal the underlying mechanism. This study provides new insights into the design and engineering of defects in transparent oxides for high-density data storage applications. Keywords: Nanocrystal growth, Self-assembly, Tin oxide, Liquid liquid interface

The structure and hydrogen absorption properties of Pd and V doped TiZrNi quasicrystals were investigated in terms of the equilibrium vapor pressure of hydrogen, and the results were compared with those of undoped samples. Rapidly quenched Ti53Zr27Ni20 alloys formed quasicrystals and absorbed hydrogen H/M (hydrogen to host metal atom ratio) value of 1.79 at room temperature. This was attributed to their structure, which contains mostly tetrahedral interstitial sites that are chemically formed by atoms having a high affinity with hydrogen. However, the relatively low equilibrium vapor pressure of hydrogen, 0.14 Torr at 300 °C, prevents TiZrNi quasicrystals for the practical application on energy storage materials. To overcome this limitation, we replaced Ti with Pd and V to increase the vapor pressure of hydrogen and investigated the properties of hydrogen absorption behaviors. Results of XRD measurements revealed that the quasicrystal structure was maintained by the replacement of Ti with a maximum of 8 at. % of Pd and V. Total amounts of the absorbed hydrogen decreased from 1.33 to 1.06 and to 1.12 of the H/M values when the Ti was replaced by 8 at. % of Pd and V, respectively, at 300 °C. The pressure-composition-temperature data measured using an automatic gas-handling system revealed that the equilibrium vapor pressure increased from 0.14 to 0.21 and to 0.56 Torr at H/M value of 0.5 when Ti atoms were replaced by 8 at. % Pd, and V, respectively, without the appearance of an impurity phase. Our results demonstrate that the replacement of Ti with Pd and V is an effective method to increase the equilibrium vapor pressure of hydrogen without a phase transformation in a TiZrNi quasicrystal system.

Summary Here, we elucidate the mechanism for Al2O3 atomic layer deposition (ALD) on LiMn2O4 (LMO) cathodes for lithium-ion batteries by using in situ and ex situ experimental characterization coupled with density functional theory (DFT) calculations. We demonstrate that not only does Al2O3 coat the LMO, but the Al heteroatom of the trimethylaluminum (TMA) precursor also dopes to interstitial sites on the LMO surface, thereby reducing the oxidation state of near-surface Mn ions. DFT calculations further suggest facile transfer of methyl groups from the TMA precursor to oxygen atoms on the LMO surface, which blocks adsorption sites for subsequent TMA adsorption. These predictions are supported by quartz crystal microbalance experiments demonstrating inhibited growth below ten ALD Al2O3 cycles, suggesting that sub-monolayer coverages of alumina are present on the LMO surface in the early stages of film growth. In comparison with fully conformal films, these sub-monolayer coatings show enhanced electrochemical capacity when cycled in coin cells.

Transition from long-range one-dimensional to short-range three-dimensional migration modes of interstitial defect clusters greatly reduces the damage accumulation in single-phase concentrated solid solution alloys under ion irradiation. A synergetic investigation with experimental, computational and modeling approaches revealed that both the resistance to void swelling and the delay in dislocation evolution in Ni-Fe alloys increased with iron concentration. This was attributed to the gradually increased sluggishness of defect migration, which enhances interstitial and vacancy recombination. Transition from long-range one-dimensional defect motion in pure nickel to short-range three-dimensional motion in concentrated Ni-Fe alloys is continuum, not abrupt, and within an iron concentration range up to 20%. The gradual transition process can be quantitatively characterized by the mean free path of the interstitial defect clusters.

We performed experiments with thin film diffusion couples to simultaneously measure diffusion coefficients of Zr, Hf, Nb and Ta parallel to the a- and c-axes of synthetic rutile in a gas mixing furnace at controlled oxygen fugacity at temperatures between 800 and $$1100\,^{\circ }\hbox {C}$$ . Depth profiles of the diffusion couples were measured using secondary-ion mass spectrometry. Some of the diffusion profiles show a concentration dependence, which indicates different diffusion mechanisms above and below a particular trace-element concentration level ( $$\sim \,1000\,\upmu \hbox {g}/\hbox {g}$$ ). The diffusion coefficients for the mechanism dominant at high-concentration levels are approximately two orders of magnitude smaller than for the low-concentration mechanism. Below the critical concentration the diffusion coefficient is constant, as consistently shown in all of the experiments. For this diffusion coefficient we have found that $$D_{\text{Zr}} \sim D_{\text{Nb}}> D_{\text{Hf}}>> D_{\text{Ta}}$$ , and diffusion is isotropic for the four elements at all investigated T and $$f\hbox {O}_2$$ conditions. At $$1000\,^{\circ }\hbox {C}$$ for log $$f\hbox {O}_2 < $$ FMQ+1, the diffusion coefficients decrease with increasing oxygen fugacity where D is proportional to $$f\hbox {O}_2^n$$ with exponents $$n \approx -0.25$$ for Zr and Hf and $$n \approx -0.30$$ for Nb and Ta. Diffusivites of Nb and Ta strongly differ from each other at all investigated conditions, thus providing the potential to fractionate these geochemical twins, as suggested earlier. The present data and literature data for Zr and Ti self diffusion are interpreted and predicted based on published quantitative point defect models. Two end-member diffusion mechanisms were identified for impurity diffusion of Zr: (i) an interstitialcy mechanism involving $$\hbox {Ti}^{3+}$$ on interstitial sites, which is dominant at approximately log $$f\hbox {O}_2 < $$ FMQ+2; (ii) a vacancy mechanism involving Ti vacancies, which is dominant at approximately log $$f\hbox {O}_2> $$ FMQ+2. The point defect calculations also explain the observed effects of heterovalent substitutions, such as $$\hbox {Nb}^{5+}$$ for $$\hbox {Ti}^{4+}$$ at high concentration levels for changes in the diffusion mechanism and hence diffusion rates. In the case of rutile, this concentration effect becomes much more sensitive to the substitution level at lower temperature. In natural rutile penta- and hexavalent cations may largely be charge balanced by mono-, di- and trivalent cations, such that the doping effect on diffusion may be reduced or may even be reversed. The Arrhenius relationships established here may therefore not be directly applicable to natural rutile. We obtained the following Arrhenius relationships (with diffusion coefficients D in $$\hbox {m}^2/\hbox {s}$$ , $$f\hbox {O}_2$$ in Pascal and T in Kelvin), which are only applicable for log $$f\hbox {O}_2 < $$ FMQ+2: $$\begin{aligned} \log D_{\text{Zr}}= & {} (-0.40 \pm 0.47) + (-0.253 \pm {0.019}) \log \frac{f\text{O}_2}{10^{-7}} - \frac{414\pm 11\,\hbox {kJ/mol}}{\text{R}T \ln 10}\\ \log D_{\text{Hf}}= & {} (-0.08 \pm 0.63) + (-0.266 \pm 0.023) \log \frac{f\text{O}_2}{10^{-7}} - \frac{428\pm 15\,\hbox {kJ/mol}}{\text{R}T \ln 10}\\ \log D_{\text{Nb}}= & {} (-0.19 \pm 0.36) + (-0.294 \pm 0.014) \log \frac{f\text{O}_2}{10^{-7}} - \frac{421\pm 9 \,\hbox {kJ/mol}}{\text{R}T \ln 10}\\ \log D_{\text{Ta}}= & {} (0.45 \pm 0.73) + (-0.304 \pm 0.015) \log \frac{f\text{O}_2}{10^{-7}} - \frac{463\pm 18\,\hbox {kJ/mol}}{\text{R}T \ln 10} \end{aligned}$$

Here we explicitly present the stability, structure, energetics and diffusion processes of H atom in 4H-SiC with and without intrinsic defects by first-principles calculations. The formation energy and interaction energy of H interstitial at eleven potential interstitial sites are calculated and compared with previous results. Besides, the structure stability of 4H-SiC is evaluated by means of deformation energy. Additionally, the energies of H atom incorporation and solution within the defective 4H-SiC have been calculated and discussed. The minimum energy paths (MEPs) with migration barriers are also calculated for atomic H by interstitial and vacancy-mediated mechanisms. In the defect-free areas of 4H-SiC matrix, interstitial H tends to diffuse three-dimensionally, which is finally trapped into the stable positions of H Si , H C , or T Si on row A. The migration barriers for vacancy-mediated migration display a rather diverse behavior. On the whole, the energy barrier by V C -mediated diffusion is slightly smaller than that by V Si -mediated diffusion, excluding the paths of BC 2 ′ → V C A and BC 2 ′ → V Si A which show a opposite manner.

We study the diffusivity of oxygen interstitials around a ( 10 1 ¯ 2 ) twin boundary in Titanium. First, we identify all possible stable interstitial sites around the twin boundary and compute the corresponding site energies and transition energy barriers for jumps between these sites, using density functional theory. We show that the site energies and the barriers are consistently lower than in bulk, suggesting the higher tendency of oxygen to segregate to the twin boundary region. Using the site and transition energies and an exact solution to the master equation, we then compute the diffusivity of oxygen in the presence of the twin boundary and find enhanced diffusivity around the boundary in all directions. Enhanced diffusivity towards the boundary determines the feasibility of oxygen segregation to favorable sites at the boundary, while increased diffusivity in the boundary plane provides a path for fast diffusion of oxygen. This result reveals the underlying mechanism governing the slow growth of ( 10 1 ¯ 2 ) twin by pinning at the segregated oxygen interstitials.

The influences of isovalent Zr 4+ doping on structure and ferromagnetic property in hydrothermally prepared nanoscale CeO 2 are investigated. Results suggest that Zr ions tend to incorporate into substitutional sites and then occupy interstitial sites or the surface at a critical doping concentration. The substituted incorporation of Zr 4+ can significantly increase structure distortion and facilitate reduction of Ce 4+ and production of oxygen vacancies (V O ). With Zr doping, the saturation magnetization ( M S ) increases and then decreases, where the maximal M S appears at Ce 0.94 Zr 0.06 O 2 sample. Air annealing Ce 0.94 Zr 0.06 O 2 sample leads to the reduction of ferromagnetism. PL analyses reveal the emergent ferromagnetism may be closely related to structure distortion and V O defects induced by Zr on substitutional sites. The V O mediated F-center exchange mechanism can be used to interpret the RT ferromagnetic behavior in Zr-doped samples.

The effects of Cu doping on thermoelectric properties and structural properties, such as lattice constant and density, were investigated for the 1/0-cubic quasicrystalline approximant Al73.3−xCuxIr26.7 (x = 0–7). We found that the lattice constant increased as the Cu concentration increased although the atomic radius of Cu is smaller than that of Al. This finding suggested that doped Cu atoms are not only substituted for Al but also added to interstitial sites in the Ir icosahedral cluster to expand the cluster volume. These suggestions are also supported by the fact that the number of atoms per unit cell determined from the density, lattice constant, and analyzed composition increased as Cu content was increased. The Seebeck coefficient (S) of all the samples exhibited metallic behavior with a positive value. The Cu concentration dependence of S showed a maximum value for the x = 3-doping sample. This result indicates that substitutional Cu atoms contribute to hole doping and interstitial Cu atoms contribute to electron doping, which stabilizes the system electronically. The present work may contribute to an understanding of the mechanism of electronic stabilization in quasicrystals and related materials over a wide composition range.

Hydrogen diffusion and solubility in disordered alloys are of paramount importance to a variety of practical applications from hydrogen storage materials to separation membranes and protection against hydrogen embrittlement. By employing density functional theory calculations we unveil the atomic-level understanding of hydrogen diffusion in disordered Ti–V–Cr alloys used for hydrogen storage. Hydrogen distribution over interstitial sites of the bcc and fcc lattices of TiV 0.8 Cr 1.2 has been simulated using a supercell approach. Taking into account both structural and energy factors we identify tetrahedral sites coordinated by three different metal atoms as the most favorable for hydrogen. The calculations carried out within the nudged elastic band method show that hydrogen diffusion between two tetrahedral site in fcc TiV 0.8. Cr 1.2 H 5.25 occurs nearby an intermediate octahedral site with the activation barrier of 0.158 eV for the most probable diffusion pathway. An estimation of the hydrogen diffusion coefficient in fcc TiV 0.8. Cr 1.2 H 5.25 at 294 K provides the value of 2.6 × 10 −11 m 2 /s that is in fair agreement with experiment data. Despite the modeling was done for a hydride of a definite composition we anticipate that the present results could be extended to Ti–V–Cr hydrides with various compositions.

Tricalcium silicate (C3S) powders were successfully prepared via a novel and facile wet-chemical route with CaC2O4 and Si(OC2H5)4 (TEOS) as raw materials. Pure C3S powders with small particle size could be synthesized at 1400 °C for 6 h. The effects of sintering temperatures on the particle size distribution of C3S powders were also investigated. The results revealed that the mean particle sizes of different sintered C3S powders were 2.11, 2.23, 2.92 and 4.01 μm at sintering temperatures of 1300 °C, 1350 °C, 1400 °C and 1450 °C, with the specific surface areas of 2850, 2700, 2060 and 1500 m2/kg, respectively. The results indicated that the variations of sintering temperature had a great influence on the particle size: higher temperatures improve diffusion of ions to the interstitial sites and therefore a faster grain growth.

Although already scientists in recent years have reported some experimental and theoretical results of La-Ni-Al series of tritium-storage alloys, several key aspects remain the subject of considerable debate. In an effort to interpret some of these unknowns, we have performed experimental and theoretical investigations for LaNi5-xAlx (x = 0, 0.25, 0.5, 0.75 and 1.0) tritium-storage alloys. Firstly, the XRD characterization indicates that the unit cell volumes of LaNi5-xAlx increase with Al content in alloys. Secondly, the PC-isotherm measurement of LaNi5-xAlx alloys shows that their hydrogen absorption/desorption plateau pressures reduce with the increase of Al content while their plateau widths narrow simultaneously. The deuterium absorption/desorption plateaus have a similar trend to hydrogen’s except for their plateaus being higher than hydrogen’s. To explain the above experimental findings, a series of calculations based on density functional theory (DFT) and frozen phonon approach have been performed. The results manifest that: (1) the partial substitutions of Al for Ni reduce the hydrogen formation energies of LaNi5-xAlxH and the number of available interstitial sites, and therefore lead to the absorption/desorption plateau pressures being reduced and the plateau widths being narrowed down at the same experimental temperatures; (2) the covalent interaction between H and Ni is an important factor for estimating the stability of LaNi5-xAlx-H system; (3) since the calculated enthalpy change ΔH is generally more accurate than the calculated entropy change ΔS with respect to the corresponding experimental value for each LaNi5-xAlx-H (or D), the curves of ΔH vs. hydrogen storage capacity instead of Van’t Hoff relation, can be used to predict the experimental plateau pressures of LaNi5-xAlx-H (D or T) at a given temperature; (4) the hydrogen isotope effect of LaNi5-xAlx-H (D or T) system can be quantitatively described as a linearity relation between ΔZPE + ΔHvib and 1 / m Q (Q = H, D, T). From the good agreement between the predicted and experimental ln ( P H / P 0 ) and ln ( P D / P 0 ) , it is deduced that predicting ln ( P T / P 0 ) of LaNi5-xAlxT is feasible. The procedure of pre-computing and comparing curves of ΔH vs. hydrogen storage capacity proposed in this paper provided an attractive tool to increase the efficiency of experimental alloying design of hydrogen (deuterium or tritium) storage materials.

In this paper, the structural, electronic and magnetic properties of Zinc-blende Ga1-xVxSb compounds, with x from dilute doping situation to extreme doping limiting, were systematically investigated by first-principles calculations. V atoms prefer to substitute the Ga atoms and the formation energy is lower in Sb-rich than Ga-rich growth condition. Meantime, the SbGa antisite defects can effectively decrease the energy barrier of substitution process, from 0.85 eV to 0.53 eV. The diffusion of V atom in GaSb lattice is through meta-stable interstitial sites with an energy barrier of 0.6 eV. At a low V concentration x = 0.0625, V atoms prefer a homogeneous distribution and an antiferromagnetic coupling among them. However, starting from x = 0.5, the magnetic coupling among V atoms changes to be ferromagnetic, due to enhanced superexchange interaction between eg and t2g states of neighbouring V atoms. At the extreme limiting of x = 1.00, we found that Zinc-blende VSb as well as its analogs VAs and VP are intrinsic ferromagneitc semiconductors, with a large change of light absorption at the curie temperature. These results indicate that Ga1-xVxSb compounds can provide a platform to design the new electronic, spintronic and optoelectronic devices., 5 pages, 5 figures

This paper investigates the formation energy, atomic structure, electronic structure and optical properties of native point defects on n-GaN (0001) surface based on the first-principles of the density functional theory. The results find that the 𝑉𝑁 is not easy to exist and the 𝑉𝐺𝑎, 𝑁𝐺𝑎 or 𝑁𝑖 defects are most likely to appear on the n-type GaN surface. The substitutional defect 𝑁𝐺𝑎 , the interstitial defect 𝑁𝑖 and the single Ga vacancy cause the conduction band to drop and the Fermi level to enter the conduction band in a deeper extent. However, both the valence band and the conduction band move up at the same time with the increase of Ga vacancies, exhibiting p-type characteristics and reducing the n-type conductivity of the surface. The N-vacancy makes the conduction band shift upwards, which reduces the n-type metal conductivity. It is also found that the reduction of photon adsorption on the surface affects the photo-emission of the surface, which is detrimental to the optoelectronic devices with n-GaN and metal contacts. This study shows that 𝑉𝐺𝑎, 𝑁𝐺𝑎 and 𝑁𝑖 native point defects all increase the doping difficulty of n-type GaN films and have a certain value for the fabrication of high-performance optoelectronic devices with n-GaN and metal contacts.

Understanding the oxidation process of active metals plays a crucial role in improving their mechanical/oxidation properties. Using in situ environmental transmission electron microscopy and density-functional theory, we firstly clarify the oxidation process of single-crystal Mg at the atomic scale by using a new double-hole technique. A unique incipient interval-layered oxidation mechanism of single-crystal Mg has been confirmed, in which O atoms intercalate through the clean (21[combining macron]1[combining macron]0) surface into the alternate-layered tetrahedral sites, forming a metastable HCP-type MgO0.5 structure. Upon the increased incorporation of oxygen at the neighboring interstitial sites, the HCP-type Mg-O tetrahedron structure sharply transforms into the FCC-type MgO oxide. In addition, a typical anisotropic growth mechanism of oxides has been identified, wherein it involves two routes: the epitaxial growth of the MgO layer and the inward migration of the MgO/Mg interface. The whole oxidation rate of single-crystal Mg is mostly determined by the inward migration rate of the MgO/Mg interface, which is about six times higher than that of the epitaxial growth rate of the MgO layer along the same orientation planes. Moreover, the inward migration rate of the (020)MgO‖(011[combining macron]0)Mg interface is about twice as large as that of the (200)MgO‖(0002)Mg interface. This continuous oxide growth is mainly related to the defects in the MgO layer, which builds effective channels for the diffusion of O and Mg atoms. The in situ double-hole observations together with theoretical calculations provide a potential trajectory to probe the oxidation fundamentals of other active metals.

CeFex (x = 0, 1, 3, 5, 10, 15 and 20 at.%) mixed oxides synthesized by an adapted Pechini method were characterized by Raman spectroscopy, high-resolution transmission electron microscopy, electron paramagnetic resonance, magnetization and 57Fe Mossbauer spectroscopy (57Fe-MS) measurements in order to evaluate the oxygen vacancies formation and the chemical environment of Fe+3 inserted into the CeO2 crystalline lattice. Fe+3 introduction into the CeO2 structure resulted in an increase of the oxygen vacancies concentration, which indicates that this is the predominant charge compensation mechanism in the formation of CeFex solid solutions by the Pechini method. Fe+3 insertion in CeO2 led to the formation of substitutional solid solutions, in which Fe+3 replaced octahedral Ce+4 sites in the crystalline lattice. Fe+3 could be found in the form of isolated sites with orthorhombic distortion or Fe+3 species in pairs or clusters coupled by strong spin–spin interactions. No evidence of Fe+3 insertion into tetrahedral interstitial sites was found. Isolated Fe+3 species showed a less distorted chemical environment and greater ionic character of the Fe–O bonds than the clusters, being the concentration of both type sites approximately equal for all the Fe+3 doped contents. It was found that pure CeO2 and all the CeFex mixed oxides presented ferromagnetic properties even at room temperature possibly due to their small crystallite size and the presence of oxygen vacancies. At high Fe+3 concentrations (above 10 at.%), probably super-exchange interactions (Fe+3–O−2–Fe+3), with an antiferromagnetic character, also took place, reducing the ferromagnetism of the CeFex mixed oxides.

Solid-state ion shuttles are of broad interest in electrochemical devices, nonvolatile memory, neuromorphic computing, and biomimicry utilizing synthetic membranes. Traditional design approaches are primarily based on substitutional doping of dissimilar valent cations in a solid lattice, which has inherent limits on dopant concentration and thereby ionic conductivity. Here, we demonstrate perovskite nickelates as Li-ion shuttles with simultaneous suppression of electronic transport via Mott transition. Electrochemically lithiated SmNiO 3 (Li-SNO) contains a large amount of mobile Li + located in interstitial sites of the perovskite approaching one dopant ion per unit cell. A significant lattice expansion associated with interstitial doping allows for fast Li + conduction with reduced activation energy. We further present a generalization of this approach with results on other rare-earth perovskite nickelates as well as dopants such as Na + . The results highlight the potential of quantum materials and emergent physics in design of ion conductors.

The nonlinear migration of C atom between nearest interstitial sites in fcc iron has been studied in the paper. It reveals an optimum migration pathway in the preferred crowdion direction in its infancy; the pathway is finally along the tetrahedral direction. This nonlinear tendency can be intensified by a repulsive force from another near neighbor C atom in the crowdion direction. We introduce an interaction model based on Coulomb’s force, which indicates that this nonlinear migration mechanism is a foregone conclusion with a certain atomic geometric configuration. However, for a multiple-C system, we find that there exists a typical preferred orientation, which is a continuously stable structure maintained by the C atoms migrating in the crowdion direction. The first neighbor migrated structure is the main formation as a result of this preferential orientation. Based on this, we derive a novel diffusion equation by introducing a proportionality coefficient $$ K_{\rho } $$ , which can be closely related to the C structures absorbed on the surface during carburization. The diffusion coefficient will increase dramatically with a small perturbation of $$ K_{\rho } $$ . Moreover, a spatially heterogeneous occupation is introduced on a much larger scale. The results not only show that it is a relatively stable state but that the C diffusion coefficient is significantly larger than that of the other disorder-free C states. Meanwhile, it provides a repulsive force for nonlinear migration in the micro-cell. As a result, a greater diffusion rate will be achieved from both spatial heterogeneity and the nonlinear migration of C atoms.

The vanadyl doped K1.98 (NH4)0.02(C2O4)2.H2O system is studied at room temperature using Electron Paramagnetic Resonance (EPR) technique. Two distinct interstitial sites for vanadyl ion are found in the potassium oxalate monohydrate crystal grown with 1% ammonium oxalate monohydrate salt. This is confirmed from angular variation of EPR spectra with static magnetic field H in the ac crystal plane. The ammonium ions seem to act as catalyst for vanadyl ions to occupy otherwise more difficult two interstitial sites in the mixed system. The formation of VO [(C2O4)4.H2O] complex is envisaged in our system and relevant ‘g’ and ‘A’ parameters are obtained through EPR studies.

The stability of binary intermetallic Laves phase YFe 2 and its hydride YFe 2 H x ( x = 0–5) are studied using first-principles calculation. Accompanied with the analysis of the hydrogen binding energy and the formation enthalpy in various interstitial sites in YFe 2 H x , a transition of the stability from cubic to orthorhombic phase is found when hydrogen concentration increases to 1.5H/f.u. It is found that the hydrogen binding energy is very sensitive to the magnetic property of neighboring atoms. To get a further insight of the transition, we take into account external strains, as well as chemical substitution at Y site. It turns out that the transition point can be tuned by strain and chemical bonding.

Difference of helium (He) agglomeration energies between period 6 elements, tantalum (Ta), tungsten (W), iridium (Ir) and gold (Au), is illustrated by using first principles calculations based on density functional theory (DFT). It is found that He in W and Ir can agglomerate more easily than Ta and Au. We investigate a relationship between the He agglomeration tendency and the growth of nanostructure by He plasma irradiation. Thus, the four metals are exposed to He plasma irradiation. Each metal has different structures after the He plasma exposure. Surface nanostructures of W and Ir are fuzzy fiber-like while these structures are not observed in Ta and Au. In the meantime, W and Ir have a tendency to agglomerate He atoms at a vacancy or interstitial sites easily. This correlation suggests that the He agglomeration may play a role for understanding the fuzz formation mechanism. Keywords: Helium plasma induced structures, Fuzz, Nanostructures, Density functional theory

To understand the role of oxide nanoparticles on the clustering behavior of helium (He) atoms in oxide dispersion strengthened (ODS) steels under irradiation, we performed comparative ab initio calculations on the energetics and migration of single He atom, the stability of small Hen (n = 2–4) clusters, and multiple He atoms trapped in the host lattices of seven oxides (Y2Ti2O7, Y2TiO5, YTiO3, Y3Al5O12, YAlO3, Y2Hf2O7, Y2Zr2O7). Energetically, He inside Y2TiO5 is most stable, followed by oxides with pyrochlore structure (i.e., Y2Hf2O7, Y2Ti2O7 and Y2Zr2O7), yttrium aluminum garnet (Y3Al5O12), and cubic perovskite structure (i.e., YTiO3 and YAlO3). The insertion energy for a single He atom in those bulk oxides is always lower than that in α-Fe, while the migration barriers show opposite trend. In Y2Ti2O7, Y2TiO5 and Y3Al5O12 lattices, there is a strong repulsion between He-He pair within one interstitial site. On the contrary, a strong He-He binding interaction within one interstitial site is found in YTiO3 and YAlO3 lattices. Meanwhile, He-He pair prefers to stay in two different interstitial sites in Y2Hf2O7 and Y2Zr2O7. After incorporation of multiple He atoms, the He atoms prefer to occupy different individual interstitial sites in Y2Ti2O7, Y2TiO5, Y3Al5O12, Y2Hf2O7 and Y2Zr2O7, while they tend to form pairs inside the same interstitial site in YTiO3 and YAlO3 due to He-He binding. Our theoretical results suggest that He atoms tend to stay in oxide nanoparticles rather than α-Fe matrix, which is beneficial to prevent the He embrittlement in ODS steels.

The structure and magnetic properties ofnanocrystalline nickel ferrite powder NiFe2O4 has been investigated using two different preparation methods, including the ceramic technique and citrate method. The synthesized powders were characterized using X-ray Diffraction (XRD) for crystallite size, X-ray density and lattice parameter calculation. The results indicated that the citrate method gives the lowest value for the lattice parameter and crystallite size (60.6 nm) in citrate method and (73.8 nm) in ceramic method. Distribution of cations among the two interstitial sites (tetrahedral and octahedral sites) has been estimated by analyzing the powder X-ray diffraction patterns by employing Rietveld refinement technique, and the results reveal the existence of samples asinverse spinelwith cubic structure and Fd-3m space group.The morphological investigations using Field Emission Scanning Electron micrograph (FE-SEM) and High Resolution Transmission Electron Microscopy (HR-TEM).The elemental analysis of samples usingEnergy Dispersive X-ray Analysis (EDAX) .Magnetic measurements of the samples at room temperature were carried out by means of vibrating sample magnetometer (VSM).

The Tm3+, Yb3+ co-doped gadolinium tungstate phosphor in presence and absence of alkali ions (i.e. Li+, Na+ and K+) has been synthesized through solid state reaction method. The structural characterization confirms the crystalline nature with coexistence of the two monoclinic phases. The phase fraction varies on addition of alkali ions. The Tm3+, Yb3+ co-doped phosphor emits intense blue and near infrared emissions centered at 472 and 793 nm due to 1G4 → 3H6 and 1G4 → 3H5 transitions, respectively and a weak red emission at 655 nm due to 1G4 → 3F4 transition of Tm3+ on excitation with 976 nm. The emission intensity of near infrared band dominates over the blue and red bands. When the alkali ions are added in the Tm3+, Yb3+ co-doped phosphor, the emission intensity of the bands is enhanced significantly due to modification in the local crystal field. The emission intensity is highest for K+ incorporation compared to Li+ and Na+ due to its occupancy at the interstitial sites. The lifetime measurement reveals an enhancement in the emission intensity. The pump power dependent emission intensity plots confirm the involvement of three photons for blue and two photons for red and NIR emissions. Thus, the Li+, Na+ and K+ incorporated Tm3+, Yb3+ co-doped gadolinium tungstate phosphor emitting intense blue and NIR radiations may be useful for photonic devices, bio-imaging and solar converters.

Metal oxynitride semiconductors with the d0 or d10 electron configuration are promising materials for nontoxic pigments and photocatalysts, but their electrical properties have scarcely been studied. Anatase TaON (δ-TaON) is a metastable polymorph of TaON, and its epitaxial thin films show good semiconducting properties such as a wide tunability of electrical conductivity and a rather high electron mobility comparable to that of anatase TiO2. However, the density of carrier electrons (ne) provided by anion vacancies is limited to ∼1 × 1020 cm–3, so establishing a method for carrier doping of anatase TaON remains a critical issue for its use in electronics applications. In this report, we used soft chemical insertion of Li into interstitial sites of anatase TaON epitaxial thin films by using an n-butyllithium solution, and the resulting material showed a higher ne (3.5 × 1020 cm–3) than anion-deficient anatase TaON films. Additionally, the Li-inserted anatase TaON showed an enhanced Hall mobility (μH) of o...

Atomistic computer simulation is used to calculate the Gibbs energy at 300 K in the α and γ modifications of Nb5Si3, which are reinforcing phases in in situ composite materials based on the Nb–Si system. The calculations are carried out for boron and carbon atoms at interstitial sites. The calculated change in the Gibbs energy ΔG300 K and crystal chemistry analysis are used to conclude about the referred localization and solubility of boron and carbon atoms in the structures of the α and γ modifications of Nb5Si3.

Summary Lithium-ion batteries with high energy density are being intensively pursued to meet the ever-growing demand for energy storage. However, the increase in energy density often comes with an elevated instability of electrode materials, causing major concerns about the reliability and safety of lithium-ion batteries. Here, we report a strategy for stabilizing cathode materials by modulating the vacant lattice sites on the particle surface. Using the high-voltage Li[Ni0.5Mn1.5]O4 as an example, we demonstrate that introduction of a 10-nm epitaxial surface layer with Al3+ in the empty 16c octahedral sites of the spinel Li[Ni0.5Mn1.5]O4 suppresses structural degradation during cycling by increasing the surface stability without interfering with the Li+ diffusion around the Al3+ sites. Control of the Al3+ concentration in the surface region was shown to be a facile process. The process was shown to stabilize long-term cycling of Li[Ni0.5Mn1.5]O4 to 5 V versus Li+/Li0.

The Mg battery cathode material, thiospinel MgxZr2S4 (0 ≤ x ≤ 1), exhibits negligible volume change (ca. 0.05%) during electrochemical cycling, providing valuable insight into the limiting factors in divalent cation intercalation. Rietveld refinement of XRD data for MgxZr2S4 electrodes at various states of charge, , coupled with EDX analysis, demonstrates that Mg2+ can be inserted into Zr2S4 at 60 °C up to x = 0.7 at a C/10 rate (up to x = 0.9 at very slow rates) and cycled with a high Coulombic efficiency of 99.75%. HAADF-STEM studies provide clear visual evidence of Mg-ion occupation in the lattice, whereas XAS studies show that Zr4+ was reduced upon Mg2+ intercalation. Operando and synchrotron XRD studies reveal the creation of two phases during the latter stages of discharge (x > 0.5) as the lattice fills and Mg2+ ions begin occupying tetrahedral (8a) sites in addition to octahedral (16c) interstitial sites. Compared to the isostructural Ti2S4 thiospinel, Zr2S4 presents a slightly larger cell volume a...

Helium solutions at eight symmetric tilt grain boundaries (GBs) in tungsten (W) have been investigated through first-principles calculations. The GBs are constructed by the coincidence site lattice (CSL) model and all interstitial sites at GBs are identified with convex deltahedra. For each GB, helium atom prefers to dissolve in interstitial sites with the lowest charge density. Interactions between the helium atom and the GBs atoms are rather localized for all eight GBs studied here, and the helium solution explicitly relates to the local environment of the interstitial site. It is found out that the helium solution energies decrease as the Voronoi volumes of interstitial sites increase, and they can be quantitatively determined by helium solution energy in tungsten clusters W n . Based on this quantitative relationship, it is easy to estimate the helium solution energy in various interstitial sites in tungsten without massive first-principles calculations. Our result provides a sound theoretical guide to design favorite grain boundaries to suppress helium segregations at GBs.

The interaction between vacancies and nitrogen atoms in fcc iron has been systematically studied by first-principles calculations. The interstitial N atoms bind strongly with vacancies into VnNm clusters, and each vacancy prefers only two N atoms that locate at the first nearest neighboring octahedral interstitial sites to the vacancy and align along the 〈1 0 0〉 directions. The number of N atoms is determined by the local lattice distortion evaluated by the expansion of atomic coordination polyhedrons with respect to the vacancy at the center. The most stable V1N2 cluster can be considered as a structural unit for the cluster development. Moreover, in larger VnNm clusters with relatively high stability, the vacancies aggregate at the center and the N atoms are around the vacancies. Then, the effect of N solute on radiation swelling depending on the N concentration is discussed from a perspective of the cluster formation. The radiation swelling increases with the N concentration because the existence of N atoms can promote the vacancy aggregation and, hence, the nucleation and growth of voids. However, as the concentration further increases, N atoms will saturate the surfaces of vacancy clusters to form barrier layers, which can hinder the combination of the VnNm clusters and the void formation.

Hydrogen embrittlement susceptibility of high strength 7xxx series Al alloys has been recognized as the critical issues in the practical use of Al alloys. In spite of the recent improvement of experimental technique, the hydrogen distribution in Al alloys is still unclear. Focusing on the interface between MgZn2 precipitates and an Al matrix, which is considered as one of the important segregation sites in these alloys, we investigated the stable η-MgZn2–Al interface, and the possible hydrogen trap sites in MgZn2 and at the η-MgZn2–Al interface via first-principles calculation. Most of the interstitial sites inside the MgZn2 crystal were not possible trap sites because their energy is relatively higher than that of other trap sites. The trap energy of the most favorable site at the η-MgZn2–Al is approximately −0.3 eV/H, which is more stable that of the interstitial site at the grain boundary. The interface between MgZn2 and Al is likely to be a possible trap site in Al alloys. Moreover, hydrogen atoms do not tend to be trapped around Zn, but a trap site around Mg is favorable; this observation is consistent with previous experimental observations.

LiBH4 is among a few chemicals with the highest hydrogen storage capacities. In this paper, the crystal structure, electronic structure and dehydrogenation properties of both pure and transition metal (TM = Fe, Co, Ni, Cu and Ti)-modified LiBH4 were investigated by using first-principles calculations based on density functional theory. According to the computing results, the occupation energies of TM-doped LiBH4 suggest that the metal atoms prefer to occupy interstitial sites rather than substitute a Li atom site. Meanwhile, the calculation results show that the TM-modified LiBH4 could have decreased stability and that all the TM substitutions may kinetically favour H-desorption, due to the decrease in hydrogen removal energy during the H atom release process from the bulk. The electronic structure further proves that the TM modification tends to weaken the B H bonding interaction, and that Ti-doped LiBH4 has a good dehydrogenation performance, which is also confirmed by the reported experimental results.

The Ruddlesden–Popper (K2NiF4) type phase La2NiO3F2 was prepared via a polymer-based fluorination of La2NiO4+d. The compound was found to crystallize in the orthorhombic space group Cccm (a = 12.8350(4) A, b = 5.7935(2) A, c = 5.4864(2) A). This structural distortion results from an ordered half occupation of the interstitial anion layers and has not been observed previously for K2NiF4-type oxyfluoride compounds. From a combination of neutron and X-ray powder diffraction and 19F magic-angle spinning NMR spectroscopy, it was found that the fluoride ions are only located on the apical anion sites, whereas the oxide ions are located on the interstitial sites. This ordering results in a weakening of the magnetic Ni–F–F–Ni superexchange interactions between the perovskite layers and a reduction of the antiferromagnetic ordering temperature to 49 K. Below 30 K, a small ferromagnetic component was found, which may be the result of a magnetic canting within the antiferromagnetic arrangement and will be the subjec...