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In the present work, samples of barium borate glasses containing different molar ratios of ZnO were prepared using the conventional melt-quenching technique. X-ray diffraction studies confirmed the amorphous nature of the studied materials. Structural analysis using FT-Infrared confirmed the incorporation of the Zn atom in the glass matrix as a ZnO4 unit and the existence of ZnO in the tetrahedral interstitial sites. TEM images for the studied materials show that the average particle size is about 20 nm and the ZnO4 structural units reside in the glass matrix with high homogeneity. Density and molar volume studies manifested an increase in the density as the amount of ZnO increases and a subsequent decrease in the molar volume. UV absorption studies showed a blue shift in the absorption peak from 343 nm to 315 nm. Additionally, an observed reversible behavior around 338 nm divides the absorption range into high energy and low energy regions. In the high energy region, both absorbance, absorption coefficient, and refractive index increased with ZnO content increment. In the low energy region, this behavior was reversed, and the calculated values of the refractive index agreed with the measured ones in this region. Studies of optical dielectric parameters showed a Debye-type relaxation process in which increasing the ZnO content shortens the sample relaxation time. Our results, collectively, suggest the studied materials for several optoelectronic device applications such as high-energy optical filters, optical switches, and frequency converters.

Hydrogen permeation experiments were performed in quenched and tempered (Q&T) low alloy steels with varying Ni contents exposed to 1 bar H2 at 30, 50 and 70 °C. From the analysis of build-up and decay transients, it is concluded that the permeation coefficient, the apparent diffusion coefficient ( D a p p ) and the concentration of hydrogen in interstitial sites on the charging surface ( C 0 ) decreases as the Ni concentration increases from 0 to 5 wt.%. The total concentration of hydrogen on the charging surface ( C 0 , r ), which includes interstitial and reversibly trapped hydrogen, is about an order of magnitude larger than C 0 . The hydrogen binding energy ( E b ) and trap density ( N r ) were calculated from the D a p p vs. temperature dependence, under the hypothesis of low trap occupancy. C 0 , r , E b and N r do not show a clear correlation with Ni content, indicating that trapping is controlled by a microstructural feature other than Ni atoms in solid solution.

Constructing non-equivalent or non-octahedral substitution is a crucial strategy to gain Mn4+-doped fluoride red phosphors with short fluorescence lifetime, whereas their structural defect impact on photoluminescence (PL) property remains unrevealed. Here, a non-equivalently doped RbSbF6:Mn4+ (RSFM) with high quantum efficiency of 88 % and thermal stability of 121 % at 425 K is newly reported to probe the defect-related PL behavior. Formation energy calculation implies that an interstitial defect was formed to balance charge and stabilize crystal structure. Concentration-dependent decay studies reveal that Mn4+ emission is quenched mainly by energy transfer to neighbor defect . The large ionic radius of Sb5+ and defect leading to a premature optimal doping (0.11 mol%) is demonstrated by refined contrast of crystal structure and substitution mode among various Mn4+-doped prototypes. A couple of medium 4T2 state energy and energy difference between Mn4+ level with valence band maximum enables its superior thermal stability. Higher defect concentration slightly aggravates this thermal quenching. Using RSFM red phosphor in white light-emitting diode offers a wide-color-gamut of 121% NTSC for backlight display. This work would provide a new perspective to understand the defect effect on the PL behavior of Mn4+ special asymmetrically doped fluorides.

(Mn,Fe)2(P,Si)-basedmaterials are promisingly applied in the room-temperature magnetic refrigeration field. In this study, Mn1.25Fe0.7P0.5Si0.5Cx (x = 0, 0.01, 0.03 and 0.05) alloys were prepared by arc-melting and then a two-stage sintering process. The effects of C doping on the crystal structure and magnetocaloric behavior are discussed. Results indicate that the Fe2P-type structure (space group of P62 m) was crystallized for all samples with weakened first-order magnetic transitions (FOMT). The Curie temperature could be altered from 223.5 K to 278.5 K with the large magnetocaloric effect (MCE) remaining by C doping. In the applied magnetic field of 5 T, the peak value of magnetic entropy change (–ΔS M) increased by 7.3% to reach 25.1 J × kg–1 × K–1. The temperature-induced entropy change (ΔS DSC) derived from DSC was slightly larger than ΔS M induced by the magnetic field. The Mn1.25Fe0.7P0.5Si0.5 alloys with large MCE can be effectively tuned by C doping because C atoms prefered to share the substitute and occupy the interstitial sites in hexagonal Fe2P-type structure.

Owing to the unique features, such as mechanically robust, low-toxic, high stability, and high thermoelectric performance, CoSb3-based skutterudite materials are among art-of-the state thermoelectric candidates. In this work, we develop a facile in-situ method for the growth of well-crystallinity (Ag, Sn) co-doped CoSb3 thin films. This preparation method can efficiently control the dopant concentration and distribution in the thin films. Both the density functional theory calculation and the experimental results suggest that Sn and Ag dopants trend to enter the lattice and preferentially fill interstitial sites. Additionally, band structure calculation results suggest that the Fermi level moves into the conduction bands due to co-doping and eventually induces the increased electrical conductivity, which agrees with the optimization of carrier concentration. Moreover, an increase in the density of state after co-doping is responsible for the increased Seebeck coefficient. As a result, the power factors of (Ag, Sn) co-doped CoSb3 thin films are greatly enhanced, and the maximum power factor achieves over 0.3 mW m−1 K−2 at 623 K, which is almost two times than that of the un-doped CoSb3 film. Multiple microstructures, including Sb vacancies and Ag/Sn interstitial atoms as point defects, and a high density of lattice distortions coupled with nano-sized Ag-rich grains, lead to all scale phonon scatterings. As a result, a reduced thermal conductivity of ∼0.28 W m−1 K−1 and a maximum ZT of ∼0.52 at 623 K are obtained from (Ag, Sn) co-doped CoSb3 thin films. This study indicates our facile in-situ growth can be used to develop high-performance dual doped CoSb3 thins.

We report here our discovery of crystallographic and interstitial sites and onsite electron correlation propelled intrinsic and derived permanent magnetic properties of critical elements lean RE(TM)5 (RE = La, Ce and TM = Fe, Co) magnet materials. A full potential linearized augmented plane wave (FP-LAPW) method within the local density approximation (LDA) is used to investigate and analyze the electronic structure and magnetism of these RE(TM)5 type structures. To better correlate the experimental results, the effective Coulomb (U) and exchange (J) interactions (Hubbard parameters) are crucial at the transition metal sites. Results show that the main propeller of magnetic anisotropy in these compounds is the cobalt atoms at the 2c sites not the 3g sites. This site-specific property and site preference energetics are used to replace 3g sites with non-critical elements such as iron that exhibits a larger magnetic moment. Based on this strategic replacement, we predict two new compounds that have a larger hardness parameter with a relatively large energy product due to the atomic dilution caused by interstitial addition of nitrogen in the compounds: CeCo2Fe3N2 and LaCo2Fe3N2.

The work here deals with the observation of structural, optical and magnetic property of Eu2+ doped SnO2 nano particles. The structure is characterized by X-ray diffraction( XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV–Vis absorption, photoluminescence (PL), and time resolved PL (TRPL) spectroscopy. The introduction of Eu affects the crystallite size and substitutes with Sn without showing any interstitial defect formation. With 1% doping as the limit for entering the crystal, the crystallite size shows expansion. Upon excitation at 400 nm, the presence of Eu2+ is approved with the absence of emission around 613 nm in the doped system. Decrease in the band gap with creation of sub-band gap states under doping is reported and with the increase in Eu2+ concentration, the increase in probability of transfer of nonradiative energy is observed. Further, magnetic properties are determined by investigating magnetization vs. applied fields. A ZFC–FC measurement for the system showing highest magnetization is also performed. To boot, the state of Eu2+ is also made confirmed with the observed EPR splitting at g = 1.88. Finally, a new approach through density functional theory has been carried out for quantitative and qualitative justifications. The minimum energy states have been computed by varying the internal positions of atoms under various defined parameters. The electronic states and density of states (DOS) behavior have been calculated for justified prediction of lattice sites and respective presence of atoms. The stable magnetic ground state has been estimated using the theoretical technique.

Iron aluminide (FeAl) inter-metallic compounds are potential candidates for structural applications at high temperatures owing to their superior corrosion resistance, high temperature oxidation, low density and inexpensive material cost. However, the presence of defects can lead to reduction in the strength and ductility of FeAl-based materials. Here we present a density functional theory (DFT) study of the effect of the presence of defects including Fe and Al vacancies as well as H dopants at the substitutional and interstitial sites at a $$\sum {{{{5}\left[ {{21}0} \right]} \mathord{\left/ {\vphantom {{{5}\left[ {{21}0} \right]} {\left( {\overline{1}\overline{2}0} \right)}}} \right. \kern-\nulldelimiterspace} {\left( {\overline{1}\overline{2}0} \right)}}}$$ ∑ 5 210 / 1 ¯ 2 ¯ 0 FeAl grain boundary focusing on the energetics. The plane wave pseudopotential code Vienna Ab initio Simulation Package (VASP) in the generalized gradient approximation (GGA) is used to carry out the computations. The formation energy calculations showed that intrinsic defects such as Fe and Al vacancies probably form at the GB, indicated by their negative formation energies. These vacancies can further form defect complexes with H impurities, indicated by lowered formation energies, compact bonds and charge gain of H atoms. Electronic structure analysis showed stronger hybridization of 1s orbitals of H with Fe and Al atoms, which leads to the stabilization of these defects resulting in degradation of material strength.

Although defect engineering is the core strategy to improve thermoelectric properties, there are limited methods to effectively modulate the designed defects. Herein, we demonstrate that a high ZT value of 1.36 at 775 K and a high average ZT value of 0.99 in the temperature range from 300 to 825 K are realized in Zn-containing PbTe by designing complex defects. By combining first-principles calculations and experiments, we show that Zn atoms occupy both Pb sites and interstitial sites in PbTe and couple with each other. The contraction stress induced via substitutional Zn on Pb sites alleviates the swelling stress by Zn atoms occupying the interstitial sites and promotes the solubility of interstitial Zn atoms in the structure of PbTe. The stabilization of Zn impurity as a complex defect extends the region of PbTe phase stability toward Pb0.995Zn0.02Te, while the solid solution region in the other direction of the ternary phase diagram is much smaller. The evolution of defects in PbTe was further explicitly corroborated by aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) and positron annihilation measurement. The Zn atoms compensate the Pb vacancies (VPb) and Zn interstitials (Zni) significantly improve the electron concentration, producing a high carrier mobility of 1467.7 cm2 V-1 s-1 for the Pb0.995Zn0.02Te sample. A high power factor of 4.11 mW m-1 K-2 is achieved for the Pb0.995Zn0.02Te sample at 306 K. This work provides new insights into understanding the nature and evolution of the defects in n-type PbTe as well as improving the electronic and thermal transport properties toward higher thermoelectric performance.

Y$_{0.9}$Gd$_{0.1}$Fe$_{2}$, which crystallizes in a C15 cubic structure, can absorb up to 5 H/f.u. and its pressure-composition isotherm displays a multiplateau behavior related to the existence of several hydrides with different crystal structures. At room temperature Y$_{0.9}$Gd$_{0.1}$Fe$_{2}$H$_{x}$ hydrides (2.9 $\le$ x $\le$ 5) crystallize in three phases with cubic structure (C1, C2 and C3), two phases with monoclinic structures (M1 and M2), and one phase with orthorhombic structure (O), with the following sequence for increasing H concentration: C1, M1, C2, M2, C3, O. Each phase exists as single phase within a H homogeneity range, and they are separated from each other by two-phase domains. The reductions of crystal symmetry are related to various hydrogen orders into interstitial sites. Weak superstructure peaks were indexed by doubling the cubic cell parameter of the cubic C2 phase. Upon heating, the monoclinic M1 and M2 and the cubic C2 phases undergo order-disorder (O-D) transitions toward a disordered cubic structure CDis. These O-D transitions are reversible with thermal hysteresis effects. The cubic C3 and orthorhombic O phases transform into a disordered cubic phase accompanied by H desorption., 16 pages, 8 figures, 2 tables

High defect tolerance has been considered a primary reason for the long charge carrier lifetime and high photoluminescence quantum yield in bulk lead halide perovskites (LHPs). On the other hand, surface defects play a critical role in determining charge carrier dynamics and optical properties, especially for LHP nanocrystals and quantum dots. Understanding the nature of surface defects and developing strategy for their effective passivation are thus of strong interest. Focusing on a prototypical LHP, CsPbBr3, our work uses first-principles calculations to reveal that interstitial sites and antisites can have lower formation energies when they form at the surface while simultaneously creating deep trap states within the bandgap. Meanwhile, the formation of halide vacancies is energetically less favorable. On the basis of a new surface defect model, we demonstrate the explicit role of molecular ligands in passivating these defects, which eliminate trap states in favor of shallow states and enhance photoluminescence.

The nano-crystalline mixed ferrites with the generic formula MnxMg1 − xFe2O4 (x = 0.0–1.0, step: 0.2) were prepared by the citrate-gel auto-combustion technique. Motivated by anomalous magnetic behaviour of coarse-grained MnFe2O4, the main aim was to study the influence of Mn2+ substitution in MgFe2O4 on magnetic structure at nano-regime. The compositional stoichiometry of the final ferrite products was ascertained by EDAX mapping and particle size for each sample was determined by powder X-ray diffraction, TEM, small-angle X-ray and neutron scattering techniques. The lattice constant increases with Mn-content due to larger cation (Mn2+) substitution. The distribution of cations in the tetrahedral (A) and octahedral (B) interstitial sites of the spinel lattice is determined by X-ray diffraction and Mossbauer spectral intensity analysis. The Mossbauer spectra at room temperature exhibit two sextets due to A- and B-sites for compositions x = 0.0, 0.2 and 1.0 while spectra showed central paramagnetic doublet superimposed on magnetic sextets for the samples with x = 0.4, 0.6 and 0.8, ascribed to the presence of superparamagnetic clusters. Thermal variation of AC susceptibility showed hump near the Curie temperature due to the presence of superparamagnetic clusters as corroborated by Mossbauer signature. The observed saturation magnetic moment (at temperature 5 K and applied field 9 T) is found lower compared to Neel's moment for the compositions with x > 0.2 which is explained on the basis of the exchange disorder of Fe3+ ions in the B-sites in Mn-containing ferrites.

The ternary Zn-Sb oxide β-Zn7Sb2O12 was prepared by solid state synthesis from ZnO and Sb2O3 at 1250 °C and a reaction time of 168 h. The crystal structure of β-Zn7Sb2O12 was solved from powder diffraction data by direct-space methods and was refined by the Rietveld technique. The title compound β-Zn7Sb2O12 crystallizes in the orthorhombic space group Cmme with a = 1210.6(1) pm, b = 1856.7(1) pm, c = 852.2(1) pm, V = 1.9154(1) nm3, and eight formula units per unit cell. The structure can be described as a distorted cubic closest packing of oxide ions with Zn2+ and Sb5+ in the tetrahedral and octahedral interstitial sites. According to group-subgroup relations, the anion packing is directly derived from the spinel structure of α-Zn7Sb2O12; however, the occupation pattern of the interstitials is completely different than in the spinel structure type. The most prominent structural feature in β-Zn7Sb2O12 is the clustering of all [ZnO4] polyhedra into a [Zn7O20] moiety representing an excerpt from the sphalerite structure. The structural model is corroborated by vibrational spectroscopy as well as density functional theory calculations. Thermal analysis reveals an irreversible phase transition of β-Zn7Sb2O12 into the α-polymorph at 1330 °C.

Electrides have been identified so far by two major routes: one is conversion of elemental metals and stoichiometric compounds by high pressure; the other is to search for electron-rich compounds, and this approach is more general. In contrast, few electron-deficient structures in existing databases have been revealed as potential electride candidates. In this work, we found an electron-deficient compound Ca5Pb3 could be transformed into electrides upon applying external pressure or strain along the c-axis, which induces the electron immigration from Pb to interstitial sites. Furthermore, the electron doping via Hf substitution of Ca atoms for Ca5Pb3 was found to be capable of tuning the interstitial electron density under ambient pressure, resulting in a new stable ternary electride Ca3Hf2Pb3, Hf-substituted Ca5Pb3. The electron-deficient electride discovered here is of novel type and can largely expand the research scope of electrides. Considering a recently reported neutral electride Na3N and the present finding, it is now clarified that electrides can be identified irrespective of stoichiometry (electron-rich, -neutral, or -poor) for compounds.

In this study, density functional theory calculations have been carried out to study the hydrogen storage properties of high entropy alloy (HEA) TiZrVMoNb. It reveals that a BCC→FCC phase transformation occurs when the hydrogen content reaches 1.5 wt% during hydrogenation process, and octahedral and tetrahedral interstitial sites are preferable for hydrogen occupation before and after phase transformation, respectively. Further energetic analyses show that different hydrogen occupations in HEAs play an important role in the thermal stability of hydrides. The maximum hydrogen storage capacity for TiZrVMoNb is predicted to be 2.65 wt%, which is comparable to the largest value of 2.7 wt% for TiZrVHfNb and larger than that of other reported HEA hydrogen storage materials reported in the literature. As compared with the previously reported HEA TiZrHfMoNb with the change of only one principal element, the TiZrVMoNb not only has much higher hydrogen storage capacity, but also has more moderate hydrogen desorption temperature. The difference in hydrogen storage properties between these two HEAs is mainly attributed to the atomic weight, site occupation, lattice distortion and chemical effect of metal elements. The present study thus suggests that the TiZrVMoNb HEA has great potential as hydrogen storage materials and proposes a strategy to enhance the hydrogen storage properties of HEAs.

Powder samples of TaH0.89 and TaD0.96 are synthesized under a hydrogen (deuterium) pressure of 2.8 GPa and a temperature of 250 °C, then quenched to the liquid nitrogen temperature, recovered to ambient pressure and studied by neutron diffraction (ND) and inelastic neutron scattering (INS). The ND study shows that both hydrogen and deuterium atoms occupy tetrahedral interstitial sites in a distorted body centered cubic (bcc) crystal structure of metal atoms, while the ordering scenarios in TaH0.89 and TaD0.96 are different. Hydrogen and deuterium atoms are ordered in a layered fashion, forming long period superstructures with space groups P 4 ¯ and P222, respectively, so that the unit cells of the crystal structures of TaH0.89 and TaD0.96 are 2 × 2 × 7 and 2 × 2 × 8 supercells of the initial cubic unit cell. The INS study demonstrates a pronounced “soft” (trumpet-like) anharmonicity of the potential well for H and D atoms.

Tritium is the key fuel in nuclear fusion reactors. With the development of the international thermonuclear experimental reactor (ITER) project, the annual requirement of tritium has increased up to several kilograms. The candidate materials for tritium storage have many shortcomings such as insufficient kinetic performance, disproportionation effect, poor oxidation resistance, and poor helium (He) retaining ability. Therefore, it is urgent to develop a novel material system which satisfies all the requirements of tritium storage materials. High-entropy alloys (HEAs) have a unique structure of severe lattice distortion and have attracted much attention as hydrogen storage materials due to their high storing capacity and great hydrogenation performance. The distorted lattice helps to provide more interstitial sites for accommodating H atoms and enhance the He retaining ability by slowing down the He diffusion in the HEA lattice. In this work, the current research status of tritium storage materials, including the background and the basic criterion of tritium storage materials, as well as the disadvantages of the current materials, has been reviewed. Moreover, the theoretical and experimental studies of HEAs, focusing on the hydrogenation properties and the defect evolution in the distorted lattice, have been summarized. The HEAs may have great potential as tritium storage materials due to their potential hydrogenation performance and He retaining ability. Finally, the existing challenges and future development directions are also proposed.

Molybdenum carbides have been believed to catalyze C–C coupling to generate aromatics from methane conversion. Herein, a systematic study of methane activation on the Mo-terminated Mo2C surfaces have been performed using density functional theory calculations. Our results indicate that the Mo-terminated β-Mo2C surface exhibits a superior activity toward methane activation. Carburization through insertion of carbon atoms into the subsurface interstitial sites of β-Mo2C reduces the reactivity towards methane activation; and complete carburization in the subsurface layer of β-Mo2C makes it behave similarly to α-Mo2C, which has a completely carburized subsurface layer, and α-MoC towards methane conversion. Consequently, dimerization of the CH* adspecies through C C coupling occurs more readily, resulting in C2H2*, a potential precursor to produce long chain hydrocarbons or aromatics. This study also demonstrates a dynamic nature of carburization of molybdenum carbides under the condition of methane activation, which is expected to play an important role in determining the activity and selectivity for, e.g., dehydro-aromatization.

Summary Thermoelectric harvesting of low-temperature waste heat offers great opportunities for sustainable energy production. However, the investigations of related thermoelectric materials and modules remain sluggish. Here, we reported a great advance in the n-type Mg3Sb1.5Bi0.5 system by minor Cu additions. Some Cu atoms preferentially occupy interstitial sites within the Mg3Sb2 lattice and significantly modified phonon modes via filling in the phonon gap and increased anharmonic phonon scattering, thereby leading to the anomalously low thermal conductivity. Simultaneously, the detrimental behavior of thermally activated electrical conductivity was completely eliminated through grain-boundary complexion engineering. These two critical roles contributed to the remarkable improvement of zT. Based on this developed high-performance material coupled with p-type α-MgAgSb-based material, a fabricated thermoelectric module rivaling long-time champion Bi2Te3, demonstrated a record-high conversion efficiency ∼7.3% at the hot-side temperature of 593 K. These results pave the way for low-temperature thermoelectric harvesting.

The design of solid electrolytes with a wide electrochemical stability window and high Li-ion conductivity is a prerequisite for the realization of all solid-state Li batteries, which promises to enable extraordinary levels of safety for the battery system and may potentially revolutionize the energy storage field. Among all the promising inorganic solid electrolytes, Li4MS4 (M = Si, Ge, and Sn) with a crystal structure of Pnma symmetry have recently been recommended due to their good air stability and ionic conductivity. Here, we employ ab initio simulations to conduct a systematic investigation of the electrochemical stability and Li conductivity of Li4MS4 compounds. Our computation results reveal that the edge-sharing and face-sharing characteristics of LiS4 and LiS6 polyhedra not only facilitate the formation of a percolating Li diffusion network but would severely destabilize the crystal structure as well, thus resulting in a rather narrow electrochemical window. Although the stronger M-S bonds manifested in Li4SiS4 can benefit the overall stability, unfortunately, it also contributes to a more rugged energy landscape that inhibits Li diffusion. Li4SnS4 with a less densely packed lattice exhibits a substantially lower energy for Li ions to be accommodated at interstitial sites, which is a trigger for high Li conductivity in the bulk material, reaching 11 mS/cm at room temperature. The fast Li diffusion occurs through the concerted migration of multiple Li ions at lattice and interstitial sites. These findings open up new possibilities for the rational design of Li4MS4 (M = Si, Ge, and Sn) solid electrolytes for next-generation Li batteries.

Abstract In this work, we highlight the often-overlooked effects of doping on the microstructure and performance of bulk thermoelectric materials to offer a broader perspective on how dopants interact with their parent material. Using PbSe doped with Na, Ag, and K as a model material system, we combine original computational, experimental, and microscopy data with established trends in material behavior, to provide an in-depth discussion of the relationship between dopants, processing, and microstructure, and their effects on thermoelectric efficiency and thermal stability. Notable observations include differences in the microstructure and mass loss of thermally treated samples of Na- and Ag-doped PbSe, as well as findings that Na and K cations exist predominantly as substitutional point defects while Ag also occupies interstitial sites and exhibits lower solubility. We discuss how these differences in point defect populations are known to affect a dopants’ ability to alter carrier concentration and how they may affect the mechanical properties of PbSe during processing. Graphic Abstract

To obtain good economic and environmental benefits, LaMgNi3.6M0.4 (M = Al, Mn, Ni, Co, Cu) alloys are investigated for the hydrogen storage. The absorption data of hydrogen in the tested alloys are measured experimentally at 373 K. The hydrogen absorption isotherms are analyzed using three models derived from statistical physics formalism. The adequate model permits to discover significant details about the absorption phenomenon via determining the density of the interstitial sites (Dm), the number of hydrogen atoms per site (n) and the energetic parameter ΔE. The results indicate that multi-atomic (n > 1) and multi-linking (n

Here, we investigate Na-doping Yb14MgSb11 as a potential route to increase carrier concentration based on an improved multiband model. Experimental transport data were collected on Yb14-xNaxMgSb11 samples prepared by ball milling and hot pressing. We show that Na increases the Seebeck coefficient and resistivity, suggesting that it behaves not as a substituent but as an interstitial electron donor under this synthesis and processing conditions, decreasing hole carrier concentration. Density functional theory (DFT) calculations of equilibrium phases, defect formation enthalpies, and band diagrams shed light on the defect-modified carrier concentrations. Depending on the equilibrium phase, Na can behave as a substitutional or interstitial defect.

The margarosanite group (now officially confirmed by IMA-CNMNC) consists of triclinic Ca-(Ba, Pb) cyclosilicates with three-membered [Si3O9]6–rings (3R), with the general formulaAB2Si3O9, whereA= Pb, Ba and Ca andB= Ca. A closest-packed arrangement of O atoms parallel to (101) hosts Si andBcations in interstitial sites in alternating layers. The 3R layer has three independent Si sites in each ring. Divalent cations occupy three independent sites: Ca inBoccupies two nonequivalent sites,Ca1 (8-fold coordinated), andCa2 (6-fold coordinated).A(=Ca3) is occupied by Pb2+(or Ba2+) in 6+4 coordination, or 6+1 when occupied by Ca; this third site occurs within the 3R-layer in a peripheral position. Three minerals belong to this group: margarosanite (ideally PbCa2Si3O9), walstromite (BaCa2Si3O9) and breyite (CaCa2Si3O9). So far, no solid solutions involving theCa1 andCa2 sites have been described. Therefore, root names depend on the composition of theCa3 site only. Isomorphic replacement at theCa3 sites has been noted. We here report data on a skarn sample from the Jakobsberg Mn–Fe oxide deposit, in Värmland, Sweden, representing intermediate compositions on the walstromite–margarosanite binary, in the rangeca.50–70% mol.% BaCa2Si3O9. The Pb-rich walstromite is associated closely with celsian, phlogopite, andradite, vesuvianite, diopside and nasonite. A crystal-structure refinement (R1= 4.8%) confirmed the structure type, and showed that theCa3 (Ba, Pb) site is split into two positions separated by 0.39 Å, with the Ba atoms found slightly more peripheral to the 3R-layers.

In fusion reactors, tritium permeation barrier (TPB) technology is one of the key scientific technologies. α-Al2O3 has been considered an ideal candidate material for TPBs. In this work, a series of first-principles calculations have been performed to investigate the dissolution, clustering and diffusion behavior of hydrogen (H) in bulk α-Al2O3. The calculation results show that the most energetically stable form of hydrogen in a perfect α-Al2O3 crystal under H2 gas annealing treatment is the H2 molecule. This can also be confirmed by the electron localization function results. The attraction between two H atoms located in first and second nearest octahedral interstitial sites (OISs) is so strong that if multiple H atoms are dissolved in α-Al2O3, these atoms can migrate toward their adjacent H atoms and form clusters, which will prevent further diffusion of H. The most stable configuration of H cluster in α-Al2O3 is 2Hi, with the smallest formation energy and the largest average binding energy. The formation energy and binding energy are similar to those of the gaseous H2 molecule. We have derived the temperature-dependent diffusivity of the H2 molecule in α-Al2O3 as D ( T ) = ( 3.65 × 10 − 7 m 2 / s ) e x p ( − 2.27 e V / K T ) , which is in good agreement with the experimental values. In addition, both the dissolution energy and migration barrier of the H2 molecule are so high that dissolution and diffusion of the H2 molecule in α-Al2O3 are very difficult, resulting in low hydrogen permeability.

Heteroatom-doped transition-metal oxides are potential non-noble-metal-based catalysts for the aerobic oxidation of alcohols because of the synergistic effects of their multiple active sites. However, the design of efficient heteroatom-doped transition-metal oxide catalysts is hindered by the complexity of the synergistic effects of multiple active sites. We have developed a practical strategy for fabricating nitrogen-doped MnO2 (N–MnO2), in which nitrogen is selectively doped at interstitial sites in MnO2. Use of N–MnO2 as a catalyst enabled additive-free aerobic oxidation of alcohols in > 99% yield at 30 ​°C. The catalytic activity of commercial MnO2 (< 1%) was negligible. Systematic studies of a series of Mn-based oxide catalysts, namely commercial MnO2, MnNxO2−x (prepared by traditional N doping by treatment with NH3), and N–MnO2 showed that N–MnO2 with abundant interstitial nitrogen dopant (1.8 ​mol%) had the best catalytic activity. Mechanistic studies suggested that the introduction of interstitial nitrogen as a dopant in MnO2 enhanced the adsorption and dissociation of oxygen on the N–MnO2 catalyst and promoted oxidative dehydrogenation of alcohols at interstitial nitrogen and oxygen vacancy sites. In situ infrared spectroscopy showed that C–N bonds (1161 ​cm−1) were formed and broken during benzyl alcohol oxidation. This confirms the importance of interstitial nitrogen in the catalytic cycle. This work provides an alternative strategy based on interstitial nitrogen doping for designing nitrogen-doped transition-metal oxides for aerobic oxidative reactions.

Boron- and cerium-doped titania (Anatase) were prepared via sol-gel method. Phase composition and morphology were assessed by X-ray diffraction (XRD), scanning electronic microscopy (SEM), BET, diffuse reflectance spectra (DRS), and XPS. Photo-electrochemistry of these materials, deposited onto fluorine-doped SnO2 (FTO), was investigated in acid and acid-containing methanol. The boron-doped sample showed the best opto-electronic properties among the investigated samples. On the other hand, the cerium-doped titania samples annihilate to a certain extent the titania surface states, however, photogenerated charge separation was limited, and certainly associated to surface Ce3+/Ce4+ species. The substitutional effect of boron ions for O sites and interstitial sites was confirmed by XRD and XPS analyses.

Exploring new structural materials with strong He damage tolerance is one of the key tasks for the development of nuclear reactors. Helium (He), one of the most common elements in the nuclear environment, often forms undesired bubbles in metallic materials and may result in void swelling as well as high-temperature intergranular embrittlement. In this study, the behaviors of He in high-entropy alloy (HEA) TiZrHfMoNb and its constituents are systematically investigated both theoretically and experimentally. Density functional theory calculations show that the He atom prefers to occupy tetrahedral and octahedral interstitial sites in a HEA. The migration pathway for He in TiZrHfMoNb is explored and the migration energy barrier is determined. Besides, the He clustering behavior in TiZrHfMoNb is investigated. Through transmission electron microscopy analysis, a smaller He bubble size is observed in TiZrHfMoNb than in Ti, which is proposed to result from the lower tendency to form He clusters, a weaker coarsening effect, and severe lattice distortion in HEA. The current study thus provides deep insights into the He behaviors in HEAs and may help to develop structural materials with enhanced He damage tolerance in nuclear reactors.

A new Group 2 bimetallic nitride fluoride phase of approximate composition SrCaNF has been prepared and characterized via high resolution single crystal X-ray diffraction. Single crystalline samples were prepared from reaction of SrF2 with Ca and Sr metal under nitrogen. Structural analysis indicates a cubic rocksalt-type phase with a unit-cell doubled along [100] relative to related M2NF rocksalt polymorphs due to ordering of N and F atoms. Sr and Ca atoms share a site. Excess F atoms present in the lattice are disordered over two crystallographically distinct interstitial sites, with charge compensation due to partial vacancies at normal F lattice positions as well as F substitution for some N atoms. There is also disorder at normal F lattice positions, which appears to correlate with the occupancy of nearby F interstitial sites. The refined composition is Sr1.01Ca0.99N0.94F1.18, and the cubic phase has space group Fd $$\overline{3}$$ m (No. 227) with a = 10.3404(10) A and Z = 16. High resolution single crystal X-ray diffraction was utilized to describe the crystal chemistry of the new ordered rocksalt-type compound, SrCaNF, which shows significant disorder, particularly with respect to positioning of F atoms.

Since the 1970s, Laves intermetallics (AB2) have been widely used in hydrogen storage technology (e.g., nickel-metal hydride batteries) due to the abundant interstitial sites and moderate metal-hydrogen bond strength (EM-H). They, however, have been rarely used in the hydrogen evolution reaction (HER) because of the same reason (i.e. moderate EM-H), which results in poor HER efficiency. In this study, by applying lanthanide contraction and ligand effect, we have successfully lowered the EM-H and substantially boosted the HER activity of Laves intermetallics (RECo2 and RERu0.5Co1.5 (RE = Pr, Tb, Y and Er)) to outperform those of commercial Pt/C catalyst. Hydrogen overpotential decreases from ErCo2 (η10 = 169 mV) to PrCo2 (η10 = 113 mV) and then to PrRu0.5Co1.5 (η10 = 29 mV). The expansion of lattice constants for PrCo2 may alleviate the obstacle of H atom diffusing through interstitial sites, while the inclusion of Ru element can raise the antibonding population of Co-Co/Ru bonds, which consequently lowers EM-H and thus elevates HER activity according to the Sabatier principle. This outcome indicates that the manipulation of the crystal structure and electronic structure factor is an efficient strategy to boost the HER activity of Laves intermetallics.

First-principles calculations have been performed to investigate the interaction between solute impurity O and H/He/vacancy irradiation defects in Ti3AlC2. The formation energy and occupation of O atoms within different defects as well as the trapping progress of O/H clusters are discussed. It is found that the O atom preferentially occupies the hexahedral interstitial site (Ihex-1) in bulk Ti3AlC2, whereas it prefers to occupy the neighbouring tetrahedral interstitial site (Itetr-2) within pre-exisiting Al monovacancy (VAl), Al divacancy (2VAl–Al) and the 2VAl–C divacancy composed of Al and C vacancies. The appearance of C vacancy could greatly reduce the oxygen formation energy and make an O atom more inclined to occupy the center of C vacancy. Vacancy could capture more O atoms than H/He atoms, where VAl and 2VAl–Al could hold up to fifteen and eighteen O atoms, respectively. Meanwhile, the O could also promote the formation of Al vacancy. On the other hand, O atoms tend to occupy the interstitial sites near the Al atomic layer and have attraction to Al atoms, which is likely to enable the O atoms to combine with the Al atoms to form a Al2O3 protective layer, thus effectively inhibiting further oxidation inside the Ti3AlC2. In addition, the H–O exhibits repulsion interaction, but strong attraction occurs in the He–O interaction. Therefore, the O atom has an inhibitory effect on the formation of the H cluster, while it could bind more He atoms to form a large number of He bubbles. Besides, the O impurity greatly reduces the trapping ability of vacancy to H atoms, and O and He have a synergistic interaction for inhibiting the aggregation of H clusters. The present results are expected to provide a new insight into the behaviour of Ti3AlC2 under irradiation and oxidation conditions so that structural materials could be better designed.

To explore the diluted magnetic semiconductors for spintronic applications, we have studied N doped Y2O3 employing density functional theory (DFT). It has been observed that the non-magnetic pristine Y2O3 attains 1.0 $${{\mu }_{{\text{B}}}}$$ magnetic moment for each defect for single N impurity and the induced ferromagnetic coupling range is sufficient to withstand room temperature ferromagnetism as estimated Curie temperature is 791 K. The partial density of states reveals that it is the N 2p orbital along with nearest Y 4d orbital that mainly contributes to induced magnetism. Moreover, the computed relative formation energy indicates that O substitute defect is synthetically more appreciative and dominant over interstitial defect. The charged defect analysis also predicts that the system remains ferromagnetic even with most probable charge defect state. All these supporting outcomes stipulate that N doped Y2O3 could be customized as a diluted magnetic semiconductor that could be fruitfully applied as a spintronic device.

We have performed quasielastic neutron scattering (QENS) experiments up to 1243 K and ab initio molecular dynamics (AIMD) simulations to investigate the Na diffusion in various phases of NaAlSiO4 (NASO), namely, low-carnegieite (L-NASO; trigonal), high-carnegieite (H-NASO; cubic) and nepheline (N-NASO; hexagonal) phases. The QENS measurements reveal Na ions localized diffusion behavior in L-NASO and N-NASO, but long-range diffusion behavior in H-NASO. The AIMD simulation supplemented the QENS measurements and showed that excess Na ions in H-NASO enhance the host network flexibility and activate the AlO4/SiO4 tetrahedra rotational modes. These framework modes enable the long-range diffusion of Na across a pathway of interstitial sites. The simulations also show Na diffusion in Na-deficient N-NASO through vacant Na sites along the hexagonal c-axis.

Hydrogen incorporation during crystal growth or other treatment has attracted research interest for a long time, but the diffusion paths and the role of additional defect sites within the lithium metal oxides (LiMO3 with M = Nb, and Ta) are still not fully understood. We investigated the hydrogen diffusion by crystal orientation- and light polarization-resolved FT-IR spectroscopy. The OH− stretching vibration is modified by the out- and in-diffusion of hydrogen using appropriate temperature and atmosphere conditions. An isotropic out- and in-diffusion in the congruent as-grown materials was observed. For C-LiNbO3 a higher diffusion rate and a lower activation energy than in C-LiTaO3 were found. In comparison to C-LiTaO3, a possible reason could be the Ta interstitial defect cluster, which limits the diffusion through the empty octahedral sites. The in-diffusion coefficients of reduced crystals are almost two orders of magnitude higher compared to those of the as-grown materials. Obviously, the hydrogen diffusion is promoted by the presence of oxygen and lithium vacancies. Since the defect sites are decorated with hydrogen, the hydrogen saturation concentration depends on the defect concentration. Finally, the same diffusion rate is observed for reduced LiTaO3 and LiNbO3. Consequently, vacancy formation is lifting the diffusion blocking by Ta interstitial defects.

It has only recently been established that doping light elements (lithium, boron, and carbon) into supported transition metals can fill interstitial sites, which can be observed by the expanded unit cell. As an example, interstitial lithium (intLi) can block H filling octahedral interstices of palladium metal lattice, which improves partial hydrogenation of alkynes to alkenes under hydrogen. In contrast, herein, we reportintLi is not found in the case of Pt/C. Instead, we observe for the first time a direct ‘substitution’ of Pt with substitutional lithium (subLi) in alternating atomic columns using scanning transmission electron microscopy-annular dark field (STEM-ADF). This ordered substitutional doping results in a contraction of the unit cell as shown by high-quality synchrotron X-ray diffraction (SXRD). The electron donation of d-band of Pt without higher orbital hybridizations bysubLi offers an alternative way for ultra-selectivity in catalytic hydrogenation of carbonyl compounds by suppressing the facile CO bond breakage that would form alcohols.

Using a combination of fluorescence and bright-field optical imaging, the solid-state packing structures of semi-confined two-layer spherical colloidal crystals were observed during modulation of an external AC electric field. Upon increasing field strength, the bottom layer of colloids (layer 1) transitioned from the entropically favored hexagonal packing structure with p6m symmetry to a square-packing structure with p4m symmetry. The packing structure of layer 2 was determined by the packing structure of layer 1, with layer 2 particles resting in, and moving in registry with, the low-energy interstitial sites of layer 1. Modulation of the field strength thus resulted in a reversible transition between a face-centered cubic crystal structure and a body-centered cubic crystal structure at low and high field strengths, respectively. These structures were found to be sensitive to the particle density in the wells, with vacancies and insertions leading to the formation of mixed crystal phases at high field strengths.

Thanks to the development of experimental high-pressure techniques and methods for crystal-structure prediction based on quantum mechanics, in the past decade, numerous new compounds, mostly binary, with atypical compositions have been predicted, and some have been synthesized. Differing from conventional solid-state materials, many of these new compounds are comprised of various homonuclear chemical species, such as dimers, trimers, pentagonal and heptagonal rings, polymeric chains, atomic layers and 3D networks. Strikingly, it has been shown that pressure can alter the chemistry of an element by activating its (semi)core electrons, unoccupied orbitals and even the non-atom-centred quantum orbitals located on the interstitial sites, leading to many new surprising phenomena. This Review provides a summary of atypical compounds that result from the effects of high pressure on either the chemical bonds or the local orbitals. We describe various unusual chemical species and motifs, show how the chemical properties of the elements are altered under pressure and illustrate how compound formation is favoured even in situations in which chemical bonds are not formed. An extraordinary new picture of chemistry emerges as we piece together these unexpected high-pressure phenomena. In marked contrast to the previously held beliefs regarding the behaviour of solids under pressure, we are learning that the quantum-mechanical features of electrons, such as those that lead to the formation of directional bonds, inhomogeneous distributions of electrons and atoms, as well as variations in symmetry, might be magnified under pressure. We discuss the influence of these phenomena on future studies that will probe chemistry at higher pressures and explore more complex chemical compositions than those that have been studied to date. High pressure leads to striking new chemistry. Many new compounds with atypical compositions and a plethora of novel chemical species can be stabilized by the formation of homonuclear bonds and the activation of core electrons, non-valence and non-atomic orbitals.

Generation of hydrogen fuel via the photocatalytic water splitting mechanism using semiconductor nanoparticles under sunlight irradiation is highly important. Moreover, the development of nanophotocatalysts for polluted water treatment is significant. In this regard, we synthesized CdS, CdS:Er (2 at%), and CdS:Er (4 at%) nanoparticles by a simple reflux route. According to the comprehensive structural analysis, Er3+ ions were incorporated into the CdS host lattice at the substitutional and interstitial sites, without altering the original structure. Photocatalytic measurements revealed that the degradation efficiency of 2 at% Er-doped CdS nanoparticles reached 100% within 100 min of visible light irradiation. In addition, CdS:Er (2 at%) nanoparticles exhibited enhanced photocatalytic hydrogen generation ability under simulated sunlight irradiation. Hence, from the obtained results, we concluded that CdS:Er (2 at%) nanoparticles are promising semiconductor photocatalytic materials for wastewater treatment as well as hydrogen fuel generation.