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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.

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.

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.

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.

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.

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.

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.

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.

Molecular dopants are of great importance in nano-chemical compounds by improving the function of inorganic electronic devices. In this article, Cu:ZnS (CZS) powders were made using the chemical method. Thin films were deposited by the physical method. The CZS films showed cubic crystal structures with a single hexagonal peak. The impact of an increase in Cu2+ dopants was investigated not only in reducing the grain size but also in reducing the optical energy gap and deviation parameters of the lattice constants. The estimated energy gaps of CZS nanostructures (NSs) were (3.70, 3.66, 3.0, and 3.76 eV) for Cu dopant (0, 1.5, 3.0, and 4.5 at.%); an indication of a blueshift. Redshift was also noticed for Cu dopant 4.5% due to interstitial sites. Moreover, the transmittance for all specimens was (70–95%) in the visible and near IR-region and reduced in the UV range (

DFT calculations were carried out to investigate hydrogen release and diffusion behaviors. Results demonstrated that MgH2/TiH2 interface is thermodynamically stable with negative adhesion energy of −1.33 J/m2 with respect to the individual MgH2 and TiH2 slabs. The formation of MgH2/TiH2 interface alters the interstice structure and space of the interstitial sites where H atoms located and then significantly lowers the dehydrogenation energy of hydrogen releasing from both the MgH2 and TiH2 slabs nearby the interface comparing the bulk MgH2 and TiH2. The smallest dehydrogenation energy of 0.06 eV/H could be reached when H releases from MgH2 side. The study also illustrates that the existence of the MgH2/TiH2 interface promotes the diffusion of hydrogen vacancy. The lowest diffusion barrier of hydrogen vacancy in the MgH2 slab (from the sublayer to the frontier layer to the interface) is estimated as 0.21 eV. Based on the present study, one can deduce that the dehydrogenation of the MgH2/TiH2 system will start by H releasing from MgH2 slab, which generates H vacancies near the interface, then the interior H of MgH2 migrates to the H vacancies (diffuse of H vacancies in the opposite direction) and releases. The TiH2 acts as a catalyst promoting the generation and diffusion of H vacancies in MgH2. Therefore synthesizing of MgH2/TiH2/MgH2 sandwich structure could be an effective approach to promote the dehydrogenation process of MgH2, and an ideal structure owning geometric hydrogen capacity of 6.45 wt%.

MCB11H12 (M: Li, Na) dodecahydro-monocarba-closo-dodecaborate salt compounds are known to have stellar superionic Li+ and Na+ conductivities in their high-temperature disordered phases, making them potentially appealing electrolytes in all-solid-state batteries. Nonetheless, it is of keen interest to search for other related materials with similar conductivities while at the same time exhibiting even lower (more device-relevant) disordering temperatures, a key challenge for this class of materials. With this in mind, the unknown structural and dynamical properties of the heavier KCB11H12 congener were investigated in detail by X-ray powder diffraction, differential scanning calorimetry, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and AC impedance measurements. This salt indeed undergoes an entropy-driven, reversible, order-disorder transformation and with a lower onset temperature (348 K upon heating and 340 K upon cooling) in comparison to the lighter LiCB11H12 and NaCB11H12 analogues. The K+ cations in both the low-T ordered monoclinic (P2(1)/c) and high-T disordered cubic (Fm (3) over barm) structures occupy octahedral interstices formed by CB11H12- anions. In the low-T structure, the anions orient themselves so as to avoid close proximity between their highly electropositive C-H vertices and the neighboring K+ cations. In the high-T structure, the anions are orientationally disordered, although to best avoid the K+ cations, the anions likely orient themselves so that their C-H axes are aligned in one of eight possible directions along the body diagonals of the cubic unit cell. Across the transition, anion reorientational jump rates change from 6.2 x 10(6) s(-1) in the low-T phase (332 K) to 2.6 x 10(10) s(-1) in the high-T phase (341 K). In tandem, K+ conductivity increases by about 30-fold across the transition, yielding a high-T phase value of 3.2 x 10(-4 )S cm(-1 )at 361 K. However, this is still about 1 to 2 orders of magnitude lower than that observed for LiCB(11)H(12 )and NaCB11H12, suggesting that the relatively larger K+ cation is much more sterically hindered than Li+ and Na+ from diffusing through the anion lattice via the network of smaller interstitial sites.

To explore the role of Li in establishing room-temperature ferromagnetism in SnO2, the structural, electronic and magnetic properties of Li-doped SnO(2)compounds were studied for different size regimes, from nanoparticles to bulk crystals. Li-doped nanoparticles show ferromagnetic ordering plus a paramagnetic contribution for particle sizes in the range of 16-51 nm, while pure SnO(2)and Li-doped compounds below and above this particular size range are diamagnetic. The magnetic moment is larger for compositions where the Li substitutes for Sn than for compositions where Li prevalently occupies interstitial sites. The observed ferromagnetic ordering in Li-doped SnO(2)nanoparticles is mainly due to the holes created when Li substitutes at a Sn site. Conversely, Li acts as an electron donor and electrons from Li may combine with holes to decrease ferromagnetism when lithium mainly occupies interstitial sites in the SnO(2)lattice.

Prediction models of the formation energies of H, B, C, N, and O atoms in various interstitial sites of hcp-Ti, Zr, and Hf crystals are developed based on machine learning. Parametric models such as linear regression and brute force search (BFS) as well as nonparametric algorithms including the support vector regression (SVR) and the Gaussian process regression (GPR) are employed. Readily accessible chemical and geometrical descriptors allow straightforward implementation of the prediction models without any expensive computational modeling. The models based on BFS, SVR, and GPR show the excellent performance with R2 > 96%.

Neutron powder diffraction profiles were collected for iron deuteride (FeDx) while the temperature decreased from 1023 to 300 K for a pressure range of 4–6 gigapascal (GPa). The ε′ deuteride with a double hexagonal close-packed (dhcp) structure, which coexisted with other stable or metastable deutrides at each temperature and pressure condition, formed solid solutions with a composition of FeD0.68(1) at 673 K and 6.1 GPa and FeD0.74(1) at 603 K and 4.8 GPa. Upon stepwise cooling to 300 K, the D-content x increased to a stoichiometric value of 1.0 to form monodeuteride FeD1.0. In the dhcp FeD1.0 at 300 K and 4.2 GPa, dissolved D atoms fully occupied the octahedral interstitial sites, slightly displaced from the octahedral centers in the dhcp metal lattice, and the dhcp sequence of close-packed Fe planes contained hcp-stacking faults at 12%. Magnetic moments with 2.11 ± 0.06 μB/Fe-atom aligned ferromagnetically in parallel on the Fe planes.

Carbon ordering in supersaturated body-centered iron was investigated by means of atomic-scale simulations. Beyond the well-known Zener ordering of carbon atoms, our results reveal a first-order transition occurring upon temperature change when a single crystal is subjected to axial compression. This ordering produces orthorhombic martensite due to unequal carbon redistribution over the three octahedral interstitial sites. The resulting phase diagram is of the rare homotectoid type. Connection is made with the thermoelastic behavior of martensitic alloys, which proves to be similar to that of shape-memory alloys.

Following nuclear decay, a daughter atom in a solid will "stay in place" if the recoil energy is less than the threshold for displacement. At high temperature, it may subsequently undergo long-range diffusion or some other kind of atomic motion. In this paper, motion of 111Cd tracer probe atoms is reconsidered following electron-capture decay of 111In in the series of In3R phases (R= rare-earth). The motion produces nuclear relaxation that was measured using the method of perturbed angular correlation. Previous measurements along the entire series of In3R phases appeared to show a crossover between two diffusional regimes. While relaxation for R= Lu-Tb is consistent with a simple vacancy diffusion mechanism, relaxation for R= Nd-La is not. More recent measurements in Pd3R phases demonstrate that the site-preference of the parent In-probe changes along the series and suggests that the same behavior occurs for daughter Cd-probes. The anomalous motion observed for R= Nd-La is attributed to "lanthanide expansion" occurring towards La end-member phases. For In3La, the Cd-tracer is found to jump away from its original location on the In-sublattice in an extremely short time, of order 0.5 ns at 1000 K and 1.2 ms at room temperature, a residence time too short to be consistent with defect-mediated diffusion. Several scenarios that can explain the relaxation are presented based on the hypothesis that daughter Cd-probes first jump to neighboring interstitial sites and then are either trapped and immobilized, undergo long-range diffusion, or persist in a localized motion in a cage., Comment: Invited contribution to Diffusion in Solids and Liquids 2019, Athens, June 2019; 11 pages, 6 figures, 2 tables

The interstitial stability and diffusion properties of helium in Li4SiO4 crystals are studied by using density functional theory (DFT) simulation. All types of interstitial sites are established. Possible helium locally stable (LS) positions in interstitial sites are examined, and the formation energies are calculated. The LS site of helium interstitial in Li4SiO4 crystals is determined, the diffusion paths and barriers of the helium between adjacent LS sites are calculated by the CI-NEB method. The results show that there are 11 different LS sites in the Li4SiO4 crystal, and the formation energies are in the range of 0.770–1.034 eV. Using CI-NEB calculations, we find that the diffusion of helium is anisotropic along different directions. The most favorable diffusion path appears at the center of the crystal and diffusion along the direction, and the diffusion barrier is 0.16 eV.

PtSe2 monolayer is previously predicted to be a two-dimensional water-splitting photocatalyst. However, the weak van der Waals (vdW) interaction between H2O and the basal surface of PtSe2 significantly undermines its photocatalytic water-splitting activities. In this work, we explore the possibility of various intrinsic defects of PtSe2 in remedying this deficiency on the basis of first-principles calculations. It is interesting to find that the introduction of Pt@Se, Se@Pt, and Se interstitial defect not only fully retain the water redox abilities of pure PtSe2 and realize spatial separation of photogenerated electrons and holes, but also can extend optical absorption range and absorption coefficients. Moreover, introduction of the three kinds of defects increase the initial weak vdW interactions between H2O and the PtSe2 surface to different extent. In particular, Pt@Se anti-site defect transform the initial weak vdW to strong chemical interaction between H2O and PtSe2 surface, and function as active reaction site. These insights demonstrate that introduction of intrinsic defects, especially the Pt@Se anti-site defect, are effective means for improving the photocatalytic water-splitting activities of PtSe2 monolayer.

Segregation of solute atoms at twin boundaries (TBs) plays a critical role in mechanical properties and thermal stability of magnesium alloys. Here, segregation structures at {10 1 ¯ 1}, {10 1 ¯ 2} and {10 1 ¯ 3} TBs are characterized in a Mg-Ag alloy by means of the atomic resolution high-angle annular dark-field technique based on scanning transmission electron microscopy. Of particular finding is the unique complex segregation at {10 1 ¯ 3} TBs, where Ag atoms occupy both substitutional and interstitial sites. By contrast, Ag atoms only substitutionally segregate at {10 1 ¯ 1} and {10 1 ¯ 2} TBs. Calculation simulation of segregation energy and three-dimensional structure of TBs helps understanding of hybrid segregation.

Structural properties of nickel-substituted cobalt ferrite nano-particles NixCo1-xFe2O4 (x=0.2,0.8) synthesized using two different methods, namely combustion and co-precipitation are studied. The structural parameters of Nickel-substituted Cobalt ferrite nano-particles confirm the formation of nano-sized particles of cubic spinel structure. Lattice parameters, density, particle size and inhomogeneity are determined while Attenuated total reflectance (ATR-IR) spectroscopy and scanning electron microscope images are studied. The ATR-IR spectra show transmission peaks, in the range around 600cm-1and 400 cm-1which respectively arise from tetrahedral and octahedral interstitial sites in the spinel lattice and found cationic exchanges between the lattices of these sites. The studies reveal that the sol–gel auto combustion method can be preferred to the co-precipitation method for producing single phase nano particles with smaller crystallite size

Influence of hydrogen concentration and defects introduced by neutron irradiation on hydrogen diffusion in tungsten has been investigated by molecular dynamics simulation at elevated temperatures. Hydrogen diffusion is shown to be significantly restrained at high concentrations due to spontaneous formation of platelet-like hydrogen clusters. For neutron irradiation defects, self-interstitials, mono-vacancies and vacancy clusters are considered. By clustering and acting as dislocation loops, self-interstitials show considerable trapping effects on hydrogen, leading to the suppression of hydrogen effective diffusion and the change of diffusion model in which hydrogen mainly diffuses along dislocation lines instead of hopping between tetrahedral interstitial sites. Moreover, an equation connecting hydrogen diffusion parameters and the total length of dislocation loops is empirically established. Different influences of mono-vacancies and vacancy clusters on hydrogen diffusion have been carefully identified. With the same vacancy concentration, hydrogen diffusivity is lower with mono-vacancies than that with vacancy clusters because more isolated trapping sites are provided by mono-vacancies. This work is not only helpful for understanding the synergistic effects of neutron irradiation and plasma interaction, but also potentially applicable for larger scale simulations as input data.

In this study, the formation energies and electronic properties of six native defects as well as H impurities in wurtzite (wz) CdSe are systematically investigated using hybrid density functional calculations. It is shown that native defects, including antisite CdSe and interstitial Cdi, may be sources of the unintentional n-type conductivity in CdSe under Se-poor conditions; meanwhile, the vacancy defect VSe is not a good donor. However, when the common H impurity is considered, it is suggested that both the substitutional impurity HSe and the interstitial impurity Hi are the dominant and effective origins of the unintentional n-type conductivity in Se-poor conditions. However, unintentional p-type conductivity in CdSe is challenging to form regardless of the growth conditions. Moreover, hybrid functional calculations of the electronic structures show that the six native point defects and the extrinsic impurities Hi and HSe will cause more or fewer changes in the band gap. Among all considered defects and impurities, it is found that only the interstitial defect Cdi introduces impurity levels into the band gap. In particular, the present hybrid functional calculations theoretically affirm that the vacancy defect VCd in CdSe can induce a 2 μB magnetic moment; however, other native defects will not introduce any magnetic moment.

Temperature-dependent oxidation of Zr–Al at different temperatures (400, 600, 800, and 1000 °C) was studied. Formation of oxygen vacancies for charge compensation and occupants of oxygen at interstitial sites in the films have contributed to changes in terms of band transition and capacitance-voltage (C–V) flatband voltage shift. Dielectric constant (k) values (12.6–17.6) were obtained by the functional metal-oxide-semiconductor (MOS) capacitor. The acquisition of an abnormal C–V curve at 400 °C might be due to the occurrence of an inadequate oxidation at this temperature. The highest k value was demonstrated at 600 °C and beyond which the k value was decreasing. Though the film at 1000 °C possessed the lowest interface trap density, its low k value and compressive strain induced film buckling have weakened the overall film quality and thus was deemed not suitable for use in MOS application. Corresponding relationship with regards to structural, morphological and optical characteristics was also discussed.

In the present work, the series of copper doped Mg-Mn ferrite nanoparticles, Mg0.9Mn0.1CuxFe2-xO4 (x = 0.0, 0.1, 0.2), have been first time prepared by using technique of solution combustion. A synthesized sample was characterized by scanning electron microscopy and x-ray diffraction. The copper content substitution has resulted an increase in size of particle (31.63–48.49 nm) as well as lattice parameter (8.38–8.42 A). The method of X-ray diffraction was utilized for investigating cations distribution of interstitial sites (tetrahedral and octahedral). The attained information of distribution of cations was then utilized to explore the various parameters related to structure like ionic radii at A and B sites, theoretical lattice and oxygen positional parameters and bond lengths and angles. The estimated values of bond angles and inter-ionic distances have suggested a decrease in super exchange interactions with copper doping content in magnesium-manganese ferrite nanoparticle matrix.

An in-depth mechanistic understanding of the electrochemical lithiation process of nickel oxide (NiO) is both fundamentally interesting and technologically relevant for its potential applications. In this study, we utilize in situ transmission electron microscopy to unravel the intricate morphological features, charge state changes and lattice orientation relationships, leading to a comprehensive understanding on the conversion process in an epitaxially grown NiO thin film. Dynamic structural and chemical imaging, in combination with first-principles calculations, reveals the first direct visualization of the intermediate phase LixNiO, in which the interstitial sites are identified to be half occupied alternately, at the intercalation stage. A topotactic phase transition is identified, indexed as NiO (001)//Ni (111) by in situ electron diffraction. The kinetics of Li-ion transport can be affected by epitaxial strain and lattice defects inside the thin-film electrodes, in which disarranged structures at the boundary can promote ion diffusion, while compressive interfacial strain can have an opposite effect. These atomic-scale insights are of general importance in understanding conversion-type electrodes and guiding the design principle for viable conversion type electrode materials.

Doping with nitrogen atoms is an effective approach to alter the electronic structures of metal oxides. However, the further identification of doping sites and their effects on catalytic activity has not been clearly addressed. Herein, N atoms were selectively doped at substitutional or interstitial sites in the MnO2 lattice for the first time by controlling the N2 plasma treatment time. The effects of N-doping sites on atomic structures, valence states and electronic structures were investigated. The results indicate that both substitutional and interstitial N-doping can significantly reduce the oxygen vacancy formation energy. Furthermore, doping with N atoms can introduce new singly ionized oxygen vacancies. But in comparison with substitutional N-doping, interstitial N-doping can effectively narrow the band gap and enhance electron transport, which is conducive to the formation of oxygen vacancies. Due to its greater number of oxygen vacancies and stronger oxygen activation ability, the interstitial N-doped MnO2 exhibited improved catalytic activity for decomposing carcinogenic HCHO compared with substitutional N-doped MnO2. This research provides a site-selective N-doping method and a deep insight into the different effects of doping sites.

A first-principles approach is employed to study the influences of the metal species Al, Zr, Mo and Tc on the mechanical properties of U3Si2. When the Al, Zr, Mo and Tc atoms diffuse into the vacancy sites, they dissolve into the lattice, as confirmed by the solution energies. It is found that the compounds of U3Si2 with low amounts of Al, Zr, Mo, and Tc in the Si vacancies or Al, Zr, and Mo in the U vacancies can behave in the manner of ductility. However, in the cases where Al, Zr, Mo and Tc occupy the interstitial sites, all the compounds are demonstrated to be brittle. Furthermore, the stress-strain relationship for the U3Si1.9375Mo0.0625 system was calculated, which illustrates the enhanced ductility. The current results indicate that the substitution of Si by carefully selected metal atoms can enhance the performance of U3Si2.

Nitrogen and carbon play an important role in the oxidation of Ti-Al intermetallic alloys in air. The insertion and diffusion of these elements in the γ -TiAl phase are investigated by first-principle computations. The accommodation of C and N atoms in several likely interstitial positions has been evaluated using density functional theory (DFT) calculations. The results show that both carbon and nitrogen prefer Ti-rich environments. Then, considering the possible jumps among the stable and metastable interstitial sites, the diffusion coefficients have also been obtained from ab initio calculations. According to the Transitional State Theory, in order to compute atomic jump rates, diffusion energy barriers and vibrational modes need to be known. Herein, barrier energies are obtained using the Climbing Image Nudged Elastic Band method. Vibrational properties are computed using the finite displacement method. Finally, diffusion coefficients are obtained solving the transport equation in the infinite time limit, using an analytical approach. The obtained results are compared to the diffusion of oxygen in γ -TiAl, investigated in previous studies. An anisotropic diffusion is obtained for all the interstitial species.

Synthesis of cadmium doped cobalt zinc ferrite (Co0.5Zn0.5Cd1.5xFe2−xO4) series with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 by solid state method and analysis of structural properties using XRD, FTIR, and SEM characterization. To understand the decomposition behavior of the precursors of samples TG/DTA analysis was carried out. TG/DTA/DSC shows that reaction is endothermic in nature and the reaction completion temperature at around 730 °C. The XRD characterization of the samples affirms the cubic spinel structure. Grains in the samples are having nature of octahedron, tetrahedron and granular depicted by SEM images. The FTIR spectra of synthesized ferrites evidenced two strong absorption bands (ν1 and ν2) in the range of 400–600 cm−1 belonging to tetrahedral (A) and octahedral (B) interstitial sites. In XRD analysis, the shrinkage of unit cell is observed at higher doping concentration. The peak (3 1 1) shown the maximum intensity for x = 0.0, whereas peak (3 1 0) shown maximum intensity for x = 0.5. Williamson Hall (WH) plot and size-strain plot (SSP) results show the variation in the grain size with change in doping concentration. The doping of cadmium plays an important role in crystal growth as observed in SEM images. In FTIR analysis, peaks shift towards lower wave number with raise in doping concentration. Keywords: Co-Zn ferrite, TG/DTA/DSC, FTIR, XRD, SEM

We performed a quantum-mechanical molecular-dynamics (MD) study of Fe3Al with and without hydrogen atoms under conditions of uniaxial deformation up to the point of fracture. Addressing a long-lasting problem of hydrogen-induced brittleness of iron-aluminides under ambient conditions, we performed our density-functional-theory (DFT) MD simulations for T = 300 K (room temperature). Our MD calculations include a series of H concentrations ranging from 0.23 to 4 at.% of H and show a clear preference of H atoms for tetrahedral-like interstitial positions within the D03 lattice of Fe3Al. In order to shed more light on these findings, we performed a series of static lattice-simulations with the H atoms located in different interstitial sites. The H atoms in two different types of octahedral sites (coordinated by either one Al and five Fe atoms or two Al and four Fe atoms) represent energy maxima. Our structural relaxation of the H atoms in the octahedral sites lead to minimization of the energy when the H atom moved away from this interstitial site into a tetrahedral-like position with four nearest neighbors representing an energy minimum. Our ab initio MD simulations of uniaxial deformation along the ⟨001⟩ crystallographic direction up to the point of fracture reveal that the hydrogen atoms are located at the newly-formed surfaces of fracture planes even for the lowest computed H concentrations. The maximum strain associated with the fracture is then lower than that of H-free Fe3Al. We thus show that the hydrogen-related fracture initiation in Fe3Al in the case of an elastic type of deformation as an intrinsic property which is active even if all other plasticity mechanism are absent. The newly created fracture surfaces are partly non-planar (not atomically flat) due to thermal motion and, in particular, the H atoms creating locally different environments.

Diffusion of hydrogen in natural alkali feldspars (Eifel sanidine and adularia from unknown locality) containing strongly bonded OH defects was investigated by D/H isotope exchange in the T range 600–1050 °C at ambient pressure and at elevated pressures up to 8 kbar. Runs at 1 atm were performed in a fused silica tube connected to a liquid D2O reservoir at room temperature. In the high- pressure experiments samples were sealed with D2O in gold capsules and processed up to 4 kbar in externally heated pressure vessels using Ar/D2O as the pressure medium. Experiments at 6–8 kbar were performed in an internally heated gas pressure vessel using the double capsule technique to minimize isotopic contamination by the pressure medium. Diffusion coefficients were determined either by measuring concentration-distance profiles of OH and OD with an IR microscope or by measuring the total exchange of oriented plates after various run durations using a macroscopic IR technique. Both methods gave consistent data. D/H interdiffusion, DD/H, is almost identical in the adularia and in the sanidine implying that the chemical composition and the degree of Al/Si disorder have minor influence on the hydrogen isotope exchange in alkali feldspars. Furthermore, no effect of crystallographic orientation was found for DD/H in both feldspars. DD/H in sanidine, however, depends on the thermal pre-treatment. Heating for several days at 900 °C leads to a lowering of D by a factor of 2.3, indicating a corresponding decrease in mobile hydrogen species. Data for sanidine pre-annealed at 900 °C are well described in the T range 600–1050 °C by $$~D_{{{\text{D/H}}}} \left( {{\text{m}}^{2} {\text{/s}}} \right) = 6.9 \cdot 10^{{ - 6}} \exp \left( {\frac{{ - 162{\text{~kJ}}/{\text{mol}}}}{{R \cdot T}}} \right)$$ D D/H m 2 /s = 6.9 · 10 - 6 exp - 162 kJ / mol R · T The diffusivity is strongly enhanced by water pressures (PH2O), i.e., in the range of 0–2 kbar. At PH2O = 2 kbar the following equation applies in the T-range of 645–800 °C: $$~D_{{D/H}} \left( {{\text{m}}^{2} /{\text{s}}} \right) = 1.2 \cdot 10^{{ - 6}} \exp \left( {\frac{{ - 131~{\text{kJ}}/{\text{mol}}}}{{R \cdot T}}} \right)$$ D D / H m 2 / s = 1.2 · 10 - 6 exp - 131 kJ / mol R · T Experiments with D2O/CO2 mixture of ratio 1:1 gave smaller exchange rates compared to pure D2O fluids, confirming that that not the pressure but the water fugacity leads to the increase in the mobility of hydrogen species. At 720 °C and pressures of 4–8 kbar, chemical diffusivities of H2O, $$\tilde{D}_{{{\text{H}}_{2} {\text{O}}}}$$ D ~ H 2 O , were determined by fitting the weighted sum of the absorbances of the OH and the OD band vs. distance. The $$\tilde{D}_{{{\text{H}}_{2} {\text{O}}}}$$ D ~ H 2 O values are similar to those reported by Kronenberg et al. (Geochim Cosmochim Acta 60:4075–4094, 1996) for dehydration of Kristallina adularia at ambient pressure. It is concluded that in both cases high concentrations of H2O molecules on interstitial sites govern the transport of hydrogen. Comparison of D/H interdiffusion to O diffusion in sanidine (Freer et al. in Phil Mag A75:485–503, 1997) implies that not only interstitial H2O but also protons contribute to the transport of hydrogen under hydrothermal conditions. On the other hand, the high DD/H at ambient pressure is attributed to an interdiffusion of protons and Na+, which is supported by Na tracerdiffusion data for sanidine (Wilangowski et al. in Defect Diffus Forum 363:79–84, 2015). A basic conclusion of this research is that hydrogen storage capacity and hydrogen diffusion in feldspars are largely determined by extrinsic defects, such as substitutional defects (i.e., Al3+ + H+ for Si4+) and associates of water molecules with vacancies. The bonding of hydrogen species to the defects can vary greatly, depending on the genesis of the feldspars, so that quantitative predictions are difficult.

Owing to global warming together with the demands for thermal energy storage in diverse fields, there is demand for transparent glasses achieving reflection of the short-wave far-infrared (IR) light from solar radiation while also absorbing the longer wavelength part. Here, we performed the plasma-assisted ion implantation using a desktop-type low-pressure fluorocarbon plasma generator system to improve the optical properties of transparent soda-lime glasses. Investigations using positron annihilation techniques for the plasma-treated glass demonstrated that the fluorocarbon species occupy the sub-nanoscale interstitial sites available in the glass network of the soda-lime glass as the intrinsic open spaces, forming an implantation layer in the shallow-surface region around a depth of 50 nm. As revealed by optical spectroscopy, the subsurface layer, due to the implanted fluorocarbon species, significantly cuts off the short-wave far-IR light around a wavelength of ∼3 µm and also acts as the absorber of the longer wavelength region from 7 to 12 µm. Plasma treatment could be a promising tool to improve the optical properties in the IR light region for various materials.

Basic knowledge about the factors and mechanisms affecting the performance of solar cells and their identification is essential when thinking of future improvements to the device. Within this paper, we investigated the current transport mechanism in GaAsN p-i-n solar cells grown with atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE). We examined the electro-optical and structural properties of a GaAsN solar cell epitaxial structure and correlated the results with temperature-dependent current-voltage measurements and deep level transient spectroscopy findings. The analysis of J-V-T measurements carried out in a wide temperature range allows for the determination of the dominant current transport mechanism in a GaAsN-based solar cell device and assign it a nitrogen interstitial defect, the presence of which was confirmed by DLTFS investigation.

The evolution/degradation of the structure and phase composition of rail head material of 100-meter differentially quenched rails after extremely long-term operation is analyzed. It is shown that similar conditions of loading result in different structural transformations on the rail head surface. The formation of lattice curvature in crystal interstitial sites and initiation of highly mobile interstitial structural states there cause a dissolution of pearlite. It occurs at a depth of ≈10 mm. It is superimposed by the formation of a nanoscale substructure in the tread surface in a layer ≈2 mm thick. The nanoparticles of the carbide phase precipitate on the boundaries of the substructure. The failure of the rail metal will proceed, in the first place, in the surface layer where a critical level of the crystal lattice curvature is formed and the concentration of interstitial vacancies is maximum.

Atomic-scale defects are essential for improving thermoelectric (TE) performance of most state-of-the-art materials by simultaneously tuning the electronic and thermal properties. However, because the plural atomic-scale defects are generally inherent and disordered in nanostructured TE materials, their complexity and ambiguity on determining TE performance remain a challenge to be solved. Furthermore, the thermal stability of atomic-scale defects in nanostructured TE materials has not been studied much so far. Herein, we report that the atomic-scale defect disorders are indispensable for high TE performance of nanostructured Ti1–xHfxNiSn1–ySby half-Heusler alloys, but gradually degraded at over 773 K, deteriorating the TE performance. It is found from the thermal annealing of nanostructured Ti0.5Hf0.5NiSn0.98Sb0.02 alloys that the annihilation of Ti,Hf/Sn antisite defects primarily reduces atomic-scale defect disorders and largely contributes to the increase of lattice thermal conductivity. Moreover, it is verified that the Ni interstitial defects mainly dominate the electronic transport properties, leading to the enhancement of power factor. Direct atomic structure observations clearly demonstrate the inherent Ni interstitial defects and the thermal vulnerability of Ti,Hf/Sn antisite defects. These results provide an important guide for the application of half-Heusler alloys with highly disordered atomic-scale defects.

WO3 electrodes coated with co-binary Cu2-xTe and Bi2Te3 thin films were fabricated for sodium-sulfur (Na–S) batteries. Film fabrication was controlled by adjusting the pH of the solution and the indium doping concentration. The phases of orthorhombic CuTe and hexagonal Cu2Te with rhombohedral Bi2Te3 were formed on the WO3 electrode. After In3+ doping, In3+ ions act as Frenkel defects in the Cu2-xTe structure. This indicated that In3+ ions are located at interstitial sites in the Cu2-xTe structure with higher defect creation energy. Furthermore, more interconnected-like nanoparticles and reduced porosity were observed, thereby indicating that indium segregation with grain boundaries presented and contributed to an enhancement of the surface mobility, nucleation density, and a smoother surface. For electrochemical characteristics, a polysulfide solution was used as a redox electrolyte for ion transport. Optimization of the pH and indium concentration attributed to improve the exchange current density (J0) and time responses for the colored and bleached states because of faster movement of Na+ and S2− ions during inter/de-intercalation. Furthermore, optimization of the electrode by adjusting the pH and doping with indium is advantageous for both Na–S and rechargeable batteries because of long life cycle, reasonably high power and energy density of 306 W/kg and 9.35 Wh/kg, respectively. The highest specific capacity (Cs) values of the charge and discharge cycles for In3+-doped electrodes are ∼ 21 and 19 mAh/g, respectively with the coulombic efficiency approximates 100% (average value of ∼96%). This approach may provide a general path for the fabrication of undoped and In3+-doped co-binary Cu2-xTe and Bi2Te3 films on WO3 electrodes and may increase our knowledge regarding Na–S batteries for further performance improvement.

A series of novel γ-Al2O3 supported Pt In bimetallic catalysts were prepared by perovskite (PTO) lattice interstitial confined reduction and compared with industrial catalyst PtIn/γ-Al2O3 in the propane dehydrogenation to propene. The physics-chemistry properties of all catalysts and precursors were characterized by BET, NH3-TPD, TPR, XRD, TEM, STEM-EDS, XPS, TG and O2-TPO techniques. The results show that the metal ions of Pt4+ and In3+ confined in PTO lattice interstitial sites were more easily reduced than those confined in PTO lattice. The lattice interstitial confinement was beneficial for the formation of small and highly dispersed Pt In bimetallic species on the surface of γ-Al2O3 supported PTO Nano islands. It is just the confinement of PTO lattice interstitial sites for appropriate In3+/In0 ratio and weak Pt In interaction and the sharing Al O bond for anchoring PTO nanoparticles and weakening the surface acid sites result in the high activity and superior stability of PtIn/LaAlO3/γ-Al2O3 in propane dehydrogenation. The initial propane conversion of PtIn/LaAlO3/γ-Al2O3 was 47%, and can be maintained at 25% after 16 h, while its propene selectivity only decreased from 96% to 90%.