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Molybdenum ditelluride (MoTe 2), a member of the transition metal dichalcogenides (TMDs), has recently garnered significant attention in the fast growing fields of two-dimensional electronics. However, despite its advantages, the intrinsic properties of MoTe 2 , like the low chemical activity of its basal plane, also resulted in several technological challenges. To overcome these limitations, several methods have been explored, with single atom doping emerging as a particularly promising approach. In this study, we employed density functional theory (DFT) to investigate the influence of single atom impurities on the chemical activity of MoTe 2. A total of 22 dopants were selected from the p-block of the periodic table, ranging from boron to bismuth. Specifically, we examined the adsorption of oxygen molecules (O 2) on the doped structures to assess their impact on layer chemical activity. Our findings revealed that doping was energetically favorable for all investigated atoms, and it had a significant effect on surface activity. Notably, doping with dopants from groups 13–15, especially those with low atomic number, results in significant increased adsorption strength, leading to weakening of the molecular bonding in O 2 by up 5.72 eV, hinting at the potential use as catalyst. Additionally, we identified certain molecules, primarily from group 17, with a remarkably high adsorption energy to charge transfer ratio. This leads to excellent sensing characteristics, where the response to adsorption in their carrier concentration is increased 100-fold over the pristine MoTe 2 , while sensor recovery is estimated between 0.01 and 2 s. [Display omitted] [ABSTRACT FROM AUTHOR]

The widely developed industry of today generates significant amounts of harmful gases, which prompts the search for modern materials allowing for their efficient and reliable detection. Transition-metal dichalcogenides (TMD) constitute well-known example of such, with particularly high potential for excellent sensing of NO 2. It is known, that the adsorption of this hazardous molecule varies on the TMD composition, however the importance of transition metal and chalcogen types were never previously contrasted. Moreover, the other NO x compounds, namely NO and N 2 , interact much less with TMD sheets, the reason for which is not yet well understood. This work utilizes density functional theory (DFT) approach to untangle these problems by examining the adsorption processes of NO 2 , NO, and N 2 on the monolayers of WS 2 , MoS 2 , and MoSe 2. The calculations allowed to establish two important conclusions: (i) the chalcogen is significantly more important than transition metal, allowing for much greater increase in adsorption of NO 2 on MoSe 2 than on WS 2 , as compared to that on MoS 2 , (ii) only molecules acting as an acceptor with respect to the TMD sheet can benefit from the enhancement coming from the composition of the latter. The gained insight can likely contribute to the informed design of devices allowing selective detection, the lack of which is a recognized problem among semiconductor sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

A promising high-strength Fe – 17.7Mn – 4.7Cr – 0.48C – 10Ni – 5Al – 4Cu wt.% Austenitic steel was solutionized, then aged for 3 or 10 h at 580 °C producing a pronounced precipitation hardening response primarily due to the formation of nanoscale NiAl precipitates. Density functional theory (DFT), molecular dynamics (MD), and discrete dislocation dynamics (DDD) calculations were combined with microstructural data from atom-probe tomography (APT), informing theoretical strengthening models to predict yield strength at different stages of precipitation as a function of NiAl size, volume fraction, and composition. These yield strength predictions were compared with experimental microhardness measurements of the various ageing conditions, including the peak microhardness of 490 HV, which corresponds to an estimated alloy yield strength of 1200 MPa. Comparing MD calculations with theoretical models showed that anti-phase boundary (APB) formation was the predominant barrier to dislocation motion posed by the NiAl precipitates. Using single dislocation particle strengthening models with NiAl APB energies calculated from DFT, good agreement was observed between DDD calculations and the 10 h peak-aged experimental measurements, while agreement with the 3 h experimental measurements required reducing the NiAl APB energy. These results demonstrate the utility of the undertaken approach integrating simulations and experiments across multiple length-scales, particularly the presented coarse-grained DDD simulation method towards modeling materials strengthened by very fine precipitates. The results further suggest that the observed NiAl precipitates may adopt an alternate crystal structure early in their formation. [Display omitted] [ABSTRACT FROM AUTHOR]

We report an unexpected yet significant precipitation-strengthening effect with remarkable thermal stability in an otherwise conventionally non-heat treatable AA3104 aluminium alloy. We reveal that a minor addition of Cu plays a critical role in the alloy's strength and thermal stability, and explain the underpinning mechanisms. The primary strengthening β′ phase can be engineered to exhibit distinctive structural characteristics, including regularly-spaced Cu atom columns at the coherent β′ /Al interfaces, stacking faults and resultant domains. Our atomistic simulations rationalise that these microscopic characteristics are directly promoted by the Cu addition. The Cu-decorated interfaces promote β′ phase nucleation and result in strong, directional covalent-like Cu-Si bonding at the β′ /Al interfaces. Specifically, the interfacial Cu columns increase the work of separation of the habit-plane interfaces and reduce the interface energy, resulting in significant strengthening and stabilising effects. The Cu columns also facilitate the stacking fault formation in the β′ phase. Collectively, these features enhance the strengthening effect and thermal stability of the precipitates. This study demonstrates the potential for exploring "new" features in "old" alloys to advance alloy science and technology. [Display omitted] [ABSTRACT FROM AUTHOR]

Density functional theory is utilized to investigate the energetics and mechanisms of sulfur loss across different stoichiometries of La 2 S 3 :CaS ceramics. These atomistic results reveal that the local atomic environment around each sulfur atom, consisting of six cation sites, can be used to predict the vacancy formation energy of the atom. Three nominal compositions are considered, 50:50, 65:35, and 90:10 La 2 S 3 :CaS, for two different atomic configurations, La 2 S 3 -like and La 3 S 4 -like. Relations were developed utilizing multivariable linear models. It is shown that the number of cation vacancies and lanthanum atoms in the local environment are among the most important factors in determining the energetics of a sulfur vacancy. Bader charge analysis reveals this is related to the degree of localization of charge change around the vacancy site and how close to the preferred oxidation states the lanthanum is. Results also suggest that while defect-free La 2 S 3 -like structures are energetically favorable, once a critical vacancy content is reached, the La 3 S 4 -like structure becomes the lower energy structure, which agrees qualitatively with recent experimental observations. This has important implications on how defect content and stoichiometry in this system are related. These findings also provide useful guidance on how these materials might best be processed. [Display omitted] [ABSTRACT FROM AUTHOR]

Processes of diffusion of As and P atoms in InP and InAs, and atomic and energy structure of group-V vacancies and interstitial P and As atoms in InP and InAs have been investigated using density functional theory. Formation energies of group-V vacancies in InP and InAs and P and As interstitial atoms in InP and InAs have been calculated with hybrid functional. The main types of migration jumps have been determined, and the energy favorable migration paths and migration barriers of As and P atoms diffusion in InP and InAs via vacancies and interstitial atoms have been calculated using climbing image nudged elastic band method. In the case of diffusion of As and P atoms in InP and InAs via interstitial atoms the diffusion process occurs via indirect interstitial mechanism. The migration energy barriers for the vacancy diffusion mechanism are 1.5–2.0 eV, the migration energy barriers for the interstitialcy mechanism are 0.3–0.6 eV. The interstitial atoms have higher formation energies compared to the formation energies of the vacancies, and total activation energies of the diffusion are comparable for the vacancy and interstitialcy mechanisms. The obtained results will be useful for modeling of the diffusion processes in semiconductor structures based on InP and InAs. [Display omitted] [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) simulations are utilized to study the absorption and diffusion of hydride ions along four types of titanium nitride grain boundaries: open and compact structures of Σ5 (210)[001] and Σ5 (310)[001]. The absorption energy into bulk vacancies ranges from approx. −0.7 eV in TiN 0.7 to −0.38 eV for a single vacancy in TiN, and shows a minor dependence on the hydrogen content in the structure. The absorption energy for vacancy sites at the grain boundaries ranges from −0.44 eV to −0.66 eV. Hydrogen absorption into interstitial sites at the grain boundaries is less favourable, in part due to a positive and fairly large zero-point energy contribution, with absorption enthalpies between −0.09 eV and 0.06 eV. The interstitial diffusion barriers are 1.34 eV and 0.83 eV in the open Σ5 (310) and Σ5 (210) grain boundaries, respectively. In the compact grain boundaries, the migrating hydrogen species changed oxidation state from a hydride ion (H0.5−) to a proton (H0.3+) at the transition state as it formed bonds to nitrogen along the diffusion path. The diffusion barriers are larger than in the corresponding open structures: 1.75 eV and 1.02 eV in the compact Σ5 (310) and Σ5 (210) structures, respectively. The considered grain boundaries and diffusion pathways cannot explain the fast interfacial hydride ion transport reported for hydrogen separation membranes based on TiN x thin films with columnar microstructure. [Display omitted] [ABSTRACT FROM AUTHOR]

Body-centered cubic (BCC) alloy systems can theoretically store double amounts of hydrogen compared with commercial metal hydrides at room temperature, and BCC high entropy alloys (HEAs) have shown the potential to reach this theoretic limit. However, the high thermodynamic stability of the dihydrides formed during hydrogen storage results in high operating temperatures. Here, by employing multi-objective Bayesian optimization-aided density functional theory calculations, we discovered 8 new HEA candidates for hydrogen storage, including the VNbCrMoMn HEA that can store 2.83 wt% hydrogen at room temperature and atmospheric pressure, vastly exceeding the hydrogen capacities of 1.38 wt% and 1.91 wt% for commercial LaNi 5 H 6 and TiFeH 2. Such a high performance of VNbCrMoMn is ascribed to the optimized hydrogen absorption thermodynamics, which is achieved under the guidance of interpretable machine learning which revealed that the thermodynamics of the first and second stages of absorption are largely determined by the bulk modulus and the number of states in the d -band, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

Machine learning interatomic potentials (ML-IAPs) enable quantum-accurate, classical molecular dynamics simulations of large systems, beyond reach of density functional theory (DFT). Yet, their efficiency and ability to predict systems larger than DFT supercells are not fully explored, posing a question regarding transferability to large-scale simulations with defects (e.g. dislocations, cracks). Here, we apply a three-step validation approach to body-centered-cubic iron. First, accuracy and efficiency are assessed by optimizing ML-IAPs based on four state-of-the-art ML packages. The Pareto front of computational speed versus testing root-mean-square-error (RMSE) is computed. Second, benchmark properties relevant to plasticity and fracture are evaluated. Their relative root-mean-square-error (Q) with respect to DFT is found to correlate with RMSE. Third, transferability of ML-IAPs to dislocations and cracks is investigated by using per-atom model uncertainty quantification. The core structures and Peierls barriers of screw, M111 and three edge dislocations are compared with DFT. Traction–separation curve and critical stress intensity factor (K Ic) are also predicted. Cleavage on the pre-existing crack plane is found to be the zero-temperature atomistic fracture mechanism of pure body-centered-cubic iron under mode-I loading, independent of ML package and training database. Quantitative predictions of dislocation glide paths and K Ic can be sensitive to database, ML package, cutoff radius, and are limited by DFT accuracy. Our results highlight the importance of validating ML-IAPs by using indicators beyond RMSE. Moreover, significant computational speed-ups can be achieved by using the most efficient ML-IAP package, yet the assessment of the accuracy and transferability should be performed with care. [Display omitted] [ABSTRACT FROM AUTHOR]

The structures of atomic clusters and GP-zones preceding precipitation in an Al-0.70Mg-0.85Si-0.15Fe-0.25Mn (wt. %) alloy have been investigated by annular dark field scanning transmission electron microscopy imaging and density functional theory calculations. One analysed condition consisted of one-month natural aging, and another was in a pre-baked state after 24 h aging at 90 °C. To quantify the effect of clusters and GP-zones on microstructure development during a subsequent isothermal artificial aging at 185 °C, hardness evolution was measured, and precipitate statistics was performed at the peak hardness corresponding to 5 h aging. Several types of clusters and GP-zones have been observed and based on structure and visual appearance named 'Disordered Frank-Kasper', 'Square', 'Binocular', and 1β", 2β", 3β", 4β". The first four are most common in the natural aged condition and are associated with a well-known influence on the initial hardness evolution. The last three are fractions of the hardening β" phase and refer to the number of structural units they contain. These GP-zones have an increased density in the pre-baked condition, leading to a rapid increase in hardness during artificial aging and to a finer microstructure of high-density small needle precipitates at peak hardness. [Display omitted] [ABSTRACT FROM AUTHOR]

The discovery of promising thermoelectric materials has often been challenged by the doping bottleneck. As an example, the n-type Zintl phases are promising thermoelectric materials but are challenging to synthesize due to intractable cation vacancies. In this work, by incorporating excess Mg and Te doping, n-type SmMg 2 Sb 2 with high thermoelectric performance has been realized. Density functional theory calculations indicate that the conduction bands extrema of SmMg 2 Sb 2 are located at the L and M points in the Brillouin zone, and the valley degeneracy is 6. The high valley degeneracy of conduction bands results in a much larger n-type density-of-state effective mass (∼2.6 m 0) compared to that of many p-type Zintl phases. With the optimization of the electron concentration, an n-type power factor ∼11.0 μW cm−1 K−2 is obtained in SmMg 2+ δ Sb 1.97 Te 0.03 (δ = 0.3). Together with the effectively reduced lattice thermal conductivity by further alloying of SmMg 2 Bi 2 , a peak zT ∼1.0 at 873 K is achieved in n-type SmMg 2+ δ Sb 1.72 Bi 0.25 Te 0.03 (δ = 0.3), demonstrating the great potential of n-type Zintl phase thermoelectric materials. By tuning the stoichiometry and Te-doping, n-type Zintl phase SmMg 2 Sb 2 was successfully obtained. The multivalley in the conduction band enables SmMg 2.3 Sb 1.72 Bi 0.25 Te 0.03 to achieve a zT value of 1.0 at 823 K, which is higher than that of all reported n-type rare-earth-based Zintl phases. [Display omitted] [ABSTRACT FROM AUTHOR]

Materials design has traditionally evolved through trial-error approaches, mainly due to the non-local relationship between microstructures and properties such as strength and toughness. We propose 'alloy informatics' as a machine learning based prototype predictive approach for alloys and compounds, using electron charge density profiles derived from first-principle calculations. We demonstrate this framework in the case of hydrogen interstitials in face-centred cubic crystals, showing that their differential electron charge density profiles capture crystal properties and defect-crystal interaction properties. Radial Distribution Functions (RDFs) of defect-induced differential charge density perturbations highlight the resulting screening effect, and, together with hydrogen Bader charges, strongly correlate to a large set of atomic properties of the metal species forming the bulk crystal. We observe the spontaneous emergence of classes of charge responses while coarse-graining over crystal compositions. Nudge-Elastic-Band calculations show that RDFs and charge features also connect to hydrogen migration energy barriers between interstitial sites. Unsupervised machine-learning on RDFs supports classification, unveiling compositional and configurational non-localities in the similarities of the perturbed densities. Electron charge density perturbations may be considered as bias-free descriptors for a large variety of defects. [Display omitted] [ABSTRACT FROM AUTHOR]

L 1 0 -ordered FeNi phase has potential as a rare-earth free permanent magnet due to its large magnetization and high Curie temperature. However, low long-range crystal ordering and weak magnetocrystalline anisotropy (K u) impede its practical use in a technologically relevant permanent magnet. Employing density functional and Monte Carlo simulations, we demonstrate the substantial improvements on structural and thermal stability, disorder-order phase transition, and intrinsic permanent magnetic properties of Fe − Ni structures. We propose that this is achievable through the complementary elemental substitutions by metal elements (M) and interstitial doping with 2 p elements. Fe 1 -x M x Ni with simple metal (M = Ga and Al) and metalloid (M = Ge and Si) elemental substitutions at x = 0.5 are broadly known as Heusler (L 2 1 ) structures with no permanent magnet characteristics. On the contrary, we find that for x = 0 − 0.5, L 1 0 -type structure is energetically favored over the Heusler-type structures. The predicted structures exhibit K u values up to approximately 2.1 MJ/m 3 , which is roughly three times that of FeNi phase (0.68 MJ/m 3), where the absolute value of K u depends on the degree of L 1 0 crystal ordering. Interstitial doping with B elevates K u further up to a maximum value of 3.9 MJ/m 3 (at 0 K), leading to room-temperature intrinsic permanent magnetic properties, including maximum energy density product (B H) max , anisotropy field μ 0 H a , and hardness parameter κ , comparable to the widely investigated MnBi and MnAl permanent magnets. These results may serve as a guideline in designing Fe − Ni based rare-earth free gap permanent magnetic materials that were previously overlooked. [Display omitted] [ABSTRACT FROM AUTHOR]

• New isothermal section measured experimentally for Fe-Nb-Ni at 1373 K. • Thermochemical properties for TCP phases (Laves_C14, δ, and μ) in Fe-Nb-Ni by first-principles and phonon calculations. • TCP phases remodeled using sublattice models corresponding to their Wyckoff positions. • Both the Fe-Nb and Fe-Nb-Ni systems remodeled with the recent experimental data from this study and those in the literature. The Fe-Nb and Fe-Nb-Ni systems are remodeled using updated sublattice models for the topologically close-packed (TCP) phases of Laves_C14, δ and μ with new experimental data and first-principles and phonon calculations based on density functional theory (DFT). Scanning electron microscopy (SEM) imaging, electron probe micro-analyzer (EPMA), and wavelength-dispersive spectroscopy (WDS) are used to determine phase compositions and tie-lines in the Fe-Nb-Ni system through a diffusion multiple isothermally treated at 1373 K. The three-, three-, and five- sublattice models are used for Laves_C14, δ, and μ phases according to their Wyckoff positions, respectively. DFT calculations are employed to predict thermochemical data as a function of temperature for Laves_C14, δ, and μ phases. The new thermodynamic description of the Fe-Nb-Ni system includes a new hexagonal phase named - hP24 - and the updates for the Fe-Nb system and reproduces better the experimental and computational thermochemical and phase equilibrium data from the present study and the literature. The new results will improve thermodynamic predictions of TCP and other phases in both Fe-based and Ni-based alloy systems. [Display omitted] [ABSTRACT FROM AUTHOR]

The interaction mechanism between the precipitates and moving dislocations is one of the key factors that governs the mechanical properties of precipitation-hardened aluminum alloys. In this study, for the first time, via a combination of atomic-resolution scanning transmission electron microscopy, image simulation, and first-principles density functional theory calculations, we have revealed the slip system for Ω ′ precipitates in the Al-Cu-Mg-Ag system. Additionally, we re-examined the case for the Ω precipitates and discovered a different slip system from those previously proposed. This study demonstrates the workflow of determining the slip system(s) for nano-sized precipitates and the current results can shed useful insights into understanding dislocation-precipitate interactions and predicting the strength of Al-Cu-Mg-Ag alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

As a new type of two-dimensional material, MXenes with increased entropy (ME/HE-MXenes) possess immense potential for exhibiting unforeseen properties, making them a compelling subject for further investigation. However, due to the difficulty in predicting and preparing stable medium-entropy MAX (ME-MAX), as precursors of ME-MXenes, only a few ME-MXenes have been synthesized successfully. Herein, we proposed a thermodynamic competition strategy that enabled the successful synthesis of a stable ME-MAX consisting of four-transition metals: Ti, V, Cr and Nb, which was first predicted by density functional theory calculation. The resulting ME-MAX with a hexagonal crystal structure and pseudo-structure of P 6 3 /mmc, possessed the chemical formula TiVCrNbAlC 3. Subsequently, the corresponding ME-MXene was prepared by selectively etching the Al layer using HF acid, obtaining the desired composition of Ti 1.1 V 1.1 Cr 0.4 Nb 1.4 C 3 T x. Furthermore, aberration-corrected scanning transmission electron microscopy analysis revealed that the MX slabs within the prepared ME-MXene contained four transition metal layers arranged in an α -configuration, which was consistent with the atomic structure of the ME-MAX. In comparison to single transition metal MXenes, the tailored ME-MXene showcased lattice distortions attributable to the highly diverse composition space, consequently leading to increased active sites and improved electrical conductivity. As a result, the annealed Ti 1.1 V 1.1 Cr 0.4 Nb 1.4 C 3 T x has higher mass capacitances when used as the supercapacitor negative electrode, with weight capacitances of 292.74 F g−1 at 2 mV s−1 and 137.20 F g−1 at 200 mV s−1. The strategy proposed in this study not only expands the realm of achievable ME-MAX compositions but also opens up new possibilities for derivative medium-entropy MXenes. We reported thermodynamically competitive strategy for the synthesis of TiVCrNbAlC 3 ME-MAX, which was subsequently etched to obtain Ti 1.1 V 1.1 Cr 0.4 Nb 1.4 C 3 T x ME-MXene. As determined by AC-STEM, the MX slabs within the synthesized ME-MXene contained four transition metal layers arranged in an α -configuration. Remarkably, when employed as the negative electrode in a supercapacitor, the ME-MXene demonstrated a higher weight capacitance of 292.74 F g−1 at 2 mV s−1, surpassing the performance of STM MXenes prepared using the same methodology. [Display omitted] [ABSTRACT FROM AUTHOR]

Density Functional Theory and Embedded Atom Method potential calculations of small self-interstitials clusters in the hexagonal close packed (hcp) structure of zirconium have been performed. It is shown that by adding two self-interstitials in the lattice, the most stable configuration is triangular and contained into the basal plane. This particular configuration has been found in density functional theory and embedded atom method potential simulations. The same work is done by inserting three self-interstitials and the triangular configuration is again found as the most stable one. The study continues by adding self-interstitials to the planar structure and by reaching seven in density functional theory and thirty in embedded atom method potential calculations. The planar defect keeps a triangular configuration until seven self-interstitials, and beyond this amount, the triangle collapses by its summits into a hexagonal configuration. By considering it, an energetic model is proposed to describe the planar defect from two to seven self-interstitials. The stability of the identified configurations and the energetic model proposed constitute an important element to take into account when predicting the microstructural evolution of zirconium-based materials under irradiation. [Display omitted] [ABSTRACT FROM AUTHOR]

This work contributes to the ongoing scientific debate on the structure of TiSiN coatings. In order to illuminate the formation of a nanocomposite structure versus the formation of a Ti 1-x Si x N solid solution, a series of TiSiN coatings was synthesized and the influence of varying N 2 pressures and the addition of Ar to the deposition atmosphere on the structure of TiSiN coatings was investigated in detail. The powdered TiSiN coatings all exhibited a lower lattice parameter than reported for TiN, which further decreased with increasing N 2 pressure, at comparable elemental compositions. For all coatings the presence of a crystalline Ti 1-x Si x N solid solution as well as an amorphous SiN x phase fraction could be detected, where more Si was incorporated into the Ti 1-x Si x N solid solution at higher pressures, due to less energetic growth conditions and the additional kinetic activation stemming from Ar ions resulted in less Si incorporation. Density functional theory calculations showed that defects only play a subordinate role for the low observed lattice parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

Zero thermal expansion (ZTE) composites reinforced by negative thermal expansion (NTE) compounds exhibiting superior dimensional stability and high thermal conductivities, are urgently needed in the modern industrial field. Unfortunately, conventional strategies for achieving ZTE composites often compromise thermal conductivity by incorporating high-content NTE particles. This study reports an overlooked factor enhancing NTE: the in-situ thermal mismatch stresses within the composites, which provide a significant driving force for lattice distortion. The 50 vol.% Cu 2 P 2 O 7 /Al-Si composite achieves isotropic ZTE, low density, and high thermal conductivity due to pressure-enhanced NTE and a tight interface structure. Synchrotron X-ray diffraction and Density Functional Theory (DFT) calculations have revealed the key mechanism of in-situ residual thermal stress in the composite contributing to the enhancement of NTE in Cu 2 P 2 O 7. This work proposes a novel design approach for high-performance ZTE materials. A new strategy to enhance the negative thermal expansion (NTE) performance by using in-situ thermal residual stress within the composite material was proposed in this work. By adding a small amount of NTE reinforcement, the high expansion aluminum alloy can be transformed into zero expansion material. Such a strategy provides a promising method to obtain zero expansion material with low density and high thermal conductivity characteristics. [Display omitted] [ABSTRACT FROM AUTHOR]

The details of the temper embrittlement mechanism in steels caused by impurities are unknown. Especially from an atomistic point of view, there are still open questions regarding their interactions with alloying elements such as Ni, Cr, and Mo. Therefore, we used density functional theory to investigate the segregation and co-segregation behavior and the resulting influence on the cohesion of three representative tilt grain boundaries in iron. The results are implemented in a multi-site and multi-component kinetic and thermodynamic model for grain boundary segregation, to gain insights into the temporal and final grain boundary coverage. Our results show that the segregation tendency of As, Sb, and Sn is stronger than that of the alloying elements and significantly mitigates the grain boundary cohesion. Depending on the GB type, interactions between Sb and Sn vary from negligible to strongly attractive, which increases the likelihood of co-segregation. The cohesion-weakening effect is further amplified when elements such as Sb, Sn, and As co-segregate, compared to their individual segregation. In contrast, the co-segregation of Ni and Cr does not significantly increase the enrichment of impurities at grain boundaries, and their impact on cohesion is found to be negligible. The ability of Mo to mitigate reversible temper embrittlement is primarily attributed to its cohesion-enhancing effect and its capability to repel tramp elements from GBs, rather than scavenging them within the bulk, as suggested by previous literature. [Display omitted] • Effects of Sn, Sb, and As with Cr, Mo, and Ni on RTE were studied using DFT. • GB enrichments studied by DFT-informed thermodynamic and kinetic simulations. • Sn, Sb and As show strong segregation tendencies and severely weaken GB cohesion. • Mo does not prevent RTE through a scavenging effect. • Mo increases the GB cohesion and, depending on the GB type, repels Sn, Sb and As. [ABSTRACT FROM AUTHOR]

ThCr 2 Si 2 -type intermetallic compounds are known to exhibit superelasticity associated with structural transitions through lattice collapse and expansion. These transitions occur via the formation and breaking of Si-type bonds, respectively, under uniaxial loading along the [0 0 1] direction. Unlike most ThCr 2 Si 2 -type intermetallic compounds, which have either an uncollapsed tetragonal structure or a collapsed tetragonal structure, SrNi 2 P 2 possesses a third type of collapsed structured: a one-third orthorhombic structure, for which one expects the occurrence of unique structural transitions and superelastic behavior. In this study, uniaxial compression and tension tests were conducted on micron-sized SrNi 2 P 2 single crystalline columns at room temperature, 200 K, and 100 K, to investigate the influence of loading direction and temperature on the superelasticity of SrNi 2 P 2. Experimental data and density functional theory calculations revealed the presence of tension-compression asymmetry in the structural transitions and superelasticity, as well as an asymmetry in their temperature dependence, due to the opposite superelastic process associated with compression (forming P-P bonds) and tension (breaking P-P bonds). Additionally, following thermodynamics, the observations suggest that this asymmetric superelasticity could lead to an opposite elastocaloric effect between compression and tension, which could be beneficial potentially in obtaining large temperature changes compared to conventional superelastic solids that show the same elastocaloric effect regardless of loading direction. These results provide an important fundamental insight into the structural transitions, superelasticity processes, and potential elastocaloric effects in SrNi 2 P 2. [Display omitted] [ABSTRACT FROM AUTHOR]

The determination of Critical Resolved Shear Stress (CRSS) in titanium for basal, prismatic, and pyramidal slip-planes without empirical constants is presented by combining Density Functional Theory (DFT) and anisotropic elasticity. A new mechanism leading to tension-compression (T-C) asymmetry in the CRSS levels has been revealed for the first time. The conditions for this asymmetry are established, involving a complex interplay between the dislocation core-structure and core-advance behavior. The three conditions for T-C asymmetry that need to be simultaneously satisfied can be summarized as: (1) a medium stacking fault width, d , (3 < d / b F < 10 , where b F is the magnitude of the Burgers vector of the full dislocation), (2) an asymmetric core-structure of the extended dislocation (ξ 1 ≠ ξ 2 , where ξ 1 and ξ 2 are the core-widths of the first and second partials, respectively), and (3) intermittent motion of the partials (Δ d / b F ≠ 0 , where Δ d is the magnitude of fluctuation in stacking fault width during intermittent motion). Pyramidal-slip in titanium satisfies all three conditions, resulting in significant T-C asymmetry. The CRSS theory considers a Wigner-Seitz (W-S) cell based domain area assigned to each lattice site for the calculations of core-energies accurately capturing the slip-plane lattice. The W-S based approach is essential due to the lower symmetry of the HCP crystal circumventing potential errors associated with the one-dimensional atomic-row approximation. Dislocation core structures are obtained for all the slip-systems in titanium showing significant distortion of the disregistry profile governing the core-advance behavior. The CRSS values predicted from the theory show agreement with the experimental CRSS levels reported in the literature. [Display omitted] [ABSTRACT FROM AUTHOR]

Defects in ferroelectric materials can cause microscopic strain and electron doping, which opens up new possibilities for unique physical properties in nanoelectronics. However, comprehending the relationship between these deep-buried defect configurations and the resulting physical properties is a long-term challenge. Here, utilizing the integrated differential phase imaging technique equipped in scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy, we show the full element-resolved atomic configuration of characteristic extrinsic defects in Nb-doped epitaxial BiFeO 3 thin films. Atomic-resolution characterization reveals that the Nb doping substitutes Fe at the center of an oxygen octahedron and creates Fe vacancies near the defect core, leading to the formation of one perovskite cell-wide BiNbO 3 chain that is expanded by 19 % in perovskite cell volume and rotated by 45° relative to the matrix lattice. Further quantitative analysis of the defect demonstrates that the ferroelectric polarization distribution around the dopant-induced defects displays a "head-to-head" configuration, indicating the accumulation of negative charges. Supported by electron energy loss spectroscopy and density functional theory calculations, the linear defect leads to one-dimensional metallic channels embedded within the ferroelectric BiFeO 3 matrix. These atomic-scale findings establish the structure-functionality relationship of extrinsic defect in Nb-doped BiFeO 3 thin films, providing new insight into their fundamental understanding and potential use in low-dimensional nanoelectronics devices. [Display omitted] Using integrated differential phase imaging in aberration-corrected STEM, a featured linear defect in Nb-doped epitaxial BiFeO 3 thin films was discovered and its full element-resolved defect configuration was determined. The defect core of the characteristic defects consists of expanded and rotated BiNbO 3 perovskite cell chain. Atomic-scale quantitative measurements and first-principles calculations demonstrate a "head-to-head" polarization configuration and metallic states of the linear defects. The results could lead to the development of low-dimensional nanoelectronics devices. [ABSTRACT FROM AUTHOR]

V 2 VI 3 -based alloys have long been established as the sole commercial material system for solid-state cooling. However, the volatility of the Se element in conventional n-type Bi 2 Te 3- x Se x leads to inconsistent reproducibility across production batches. Here, we unveil an innovative, highly reproducible n-type Bi 0.5 Sb 1.5 Te 3 alloy, realized through strategic manipulation of native point defect. The initial Bi 0.5 Sb 1.5 Te 3 is saturated with antisite defects, imbuing it with pronounced p-type conductivity. Our investigation, underpinned by the electronegativity and atomic size model and validated through density functional theory calculation, reveals that the replacement of Sb by In in the Bi 0.5 Sb 1.5- x In x Te 3 system effectively elevates the formation energy of negatively charged antisite defect, while simultaneously diminishing that of positively charged anion vacancy. This alteration in the dominant point defect type catalyzes a p-n type transition, prominently observed at around x = 0.15. We believe this constitutes the inaugural disclosure of a n-type Sb 2 Te 3 -rich bulk material. The observed low zT ∼ 0.16 at 360 K in n-type Bi 0.5 Sb 1.05 In 0.45 Te 3 , attributed to low electron mobility, is a focal point for ongoing performance enhancement efforts. These results not only enrich the comprehension of intrinsic point defect manipulation in the V 2 VI 3 system, but also pave the way for the systematic evolution and realization of innovative, high-efficiency, and consistently reproducible n-type Bi 2- x Sb x Te 3 alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Permanent magnets (PMs) based on manganese show significant potential for applications in electric motors and devices as an alternative to Rare-earth PMs (REPMs). The metastable ferromagnetic τ phase of the Mn-Al system has magnetic performance between the REPM Nd-Fe-B magnets and the lower performance ferrite magnets. However, the maximum performance in Mn-Al PMs has not reached its theoretical limit, in part due to challenges in controlling crystalline defects such as anti-phase boundaries (APBs). APBs act as nucleation sites for domain reversal in Mn-Al and negatively affect magnetization by interrupting the L1 0 ordering, placing Mn atoms into AFM-coupled Mn-Mn configurations. In this study, Ab-initio modeling was used to screen ternary elements based on their affinity to segregate to the APB and on their preference for FM configuration. The ternary element addition of 1 at.% Ti lowered the density of APBs as observed in a transmission electron microscope. The 1 at.% Ti addition was observed to improve (BH) max over the base alloy, by preserving H ci and improving M r. It also significantly increased the fraction of twin boundaries in the τ phase. AFM behavior that was observed in the base alloy during T C heating experiments (Néel behavior) and high-field VSM measurements (spin-flop behavior) was effectively suppressed with the addition of Ti. Additionally, the Ti addition thermally stabilized H ci at 550 °C, improving τ phase processability. Other candidate elements, Cr, V, and Zr, were modeled to have similar potential for minimizing APBs when added to Mn-Al. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigates the structure, microstructure, and transport properties of off-stoichiometric GeTe (off-GeTe). In a narrow range of 50–53 at% Te, both the rhombohedral a -GeTe and orthorhombic g -GeTe phases coexist. Despite their similar chemical composition, GeTe and off-GeTe alloys exhibit distinct microstructural and thermal/electronic properties. Theoretical density functional theory (DFT) calculations were employed to verify that changes in the Ge/Te ratios influence the concentration of Ge vacancies, leading to a significant alteration in transport properties despite minor variations in chemical compositions. The off-GeTe alloy, which is free of Ge precipitates, displays defective domain boundaries, showcasing a non-typical herringbone nanostructure that is unprecedented for GeTe-based materials. Notably, the phase transition temperature of off-GeTe, at 620K, differs from its peak zT temperature of 698K. Moreover, a TE device incorporating off-GeTe demonstrates superior interfacial stability and higher energy conversion efficiency compared to its stoichiometric GeTe counterpart. Consequently, off-GeTe demonstrates superior TE performance and enhanced interfacial stability compared to stoichiometric GeTe. The addition of Sb to off-GeTe further improves its potential for TE applications by lifting the single-leg conversion efficiency greater than 3%. [Display omitted] [ABSTRACT FROM AUTHOR]

Magnetic compounds possessing an intrinsic combination of near-zero magnetization with high magnetic anisotropy are highly desirable for spinronic applications and memory recording. A comprehensive study of Sm 7 Pd 3 binary compound uncovered a unique combination of strong magnetoelastic behavior, very low net magnetization, and exceptionally high magnetic coercivity. The temperature-dependent X-ray synchrotron powder diffraction study indicates the abrupt changes in the compound's lattice parameters at the magnetic ordering temperature of T C =169 K, although the crystal structure remains non-centrosymmetric hexagonal Th 7 Fe 3 -type down to 6 K. Density functional theory calculations confirm high intrinsic magnetocrystalline anisotropy of Sm 7 Pd 3 , which explains the extremely large coercivity of the polycrystalline sample, up to H cr = 130 kOe at 2 K. This discovery brings to life a novel class of highly anisotropic materials that are distinctly different from known spintronic materials, making them interesting future systems for magnetic memory research. [Display omitted] [ABSTRACT FROM AUTHOR]

The oxidation behavior of zirconium alloy in high-temperature steam plays a dominant role in the operation of nuclear reactors under accident conditions. The present work investigated the effect of Sn on the oxidation behavior of zirconium alloys in high-temperature steam at 1000 °C. The results of scanning electron microscopy (SEM), metallographic microscopy and synchrotron X-ray diffraction (S-XRD) analyses show that there are three layers in the oxidized sample, including prior β-Zr, α-Zr(O) and ZrO 2. High resolution analyses conducted in these layers by transmission electron microscopy (TEM) show that Sn atoms segregate around the oxide-metal (O-M interface and Zr-Sn intermetallic precipitates only present in the oxide film. Clear atomic arrangements of Zr 5 Sn 3 were obtained by TEM, resulting in accurate identification of the Zr-Sn intermetallic phase. Also, TEM energy dispersive spectroscopy (EDS) maps show that Zr-Sn particles invariably accompany the segregation or precipitation of Nb. However, no clear precipitation sequence was observed, which suggests that a co-precipitation mechanism of Sn and Nb is in operation. As oxidation proceeds, nanovoids next to the Zr-Sn intermetallic particles were observed accompanied by local areas deficient in oxygen, identified as ZrO. Combining the interdiffusion trend obtained by Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, a mechanism for the transformation from the Zr-Sn intermetallic precipitates to nanovoids was proposed. This proposed mechanism may shed new light into the role of Sn in the oxidation resistance of zirconium alloy under LOCA conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Intermetallic compounds AuSn with a double hexagonal close-packed (dhcp) structure and Au 5 Sn with a trigonal structure constituted the eutectic Au-20Sn alloy. By using high-resolution scanning transmission electron microscopy, first-principles density functional theory calculations, and topological models, we characterized three deformation twins, { 10 1 ¯ 2 } twin in AuSn and { 10 1 ¯ 2 ¯ } and { 10 1 ¯ 1 } twins in Au 5 Sn and quantified their elementary parameters, K 1 , η 1 , K 2 and η 2. { 10 1 ¯ 2 } twin in AuSn has six equivalent variants corresponding the dhcp structure. The elementary twinning disconnection (TD) is ( b 3 ,3h 0) with the shear vector b 3 = 0.062 〈 10 1 ¯ 1 ¯ 〉 and the step height of three atomic layers. The trigonal structure of Au 5 Sn exhibits a three-fold rotation symmetry around the [ 0001 ] axis, { 10 1 ¯ 2 ¯ } and { 10 1 ¯ 1 } twins in Au 5 Sn have two sets of three equivalent variants. These twins could be either conventional twins or pseudo twins. For conventional { 10 1 ¯ 2 } twins with low energy twin boundary, the elementary TD is ( b 3 , 3h 0) with b 3 = 0.059 〈 10 1 ¯ 1 〉 and the step height of three atomic layers. For two sets of { 10 1 ¯ 1 } twins, the elementary TD is ( b 6 , 6h 0) with shear vector b 6 = 0.086 〈 1 ¯ 012 〉 and the step height of six atomic layers. Pseudo twins could be created through the gliding of ( b 2 , 2h 0) TDs. This work provides the precise knowledge and comprehensive understanding of deformation twins in intermetallic compounds with complex structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding solute segregation thermodynamics is the first step in investigating grain boundary (GB) properties, such as strong yttrium (Y) effects on grain growth and texture evolution in micro-scale polycrystalline magnesium (Mg) alloys. To estimate the average GB segregation behavior in low-solute-concentration Mg alloys (e.g., 2 at.% Y), a state-of-the-art spectral approach is applied based on a per-site segregation energy spectrum for Y solute atoms at zero K obtained from molecular statistics (MS) simulations of ∼ 1 0 4 GB sites in Mg symmetric tilt GBs (STGBs). Although selected MS simulation results are consistent with verification by density functional theory (DFT) calculations, estimates of average segregation tendency based on the zero-K energy spectrum deviate from experimental observations. To resolve this problem, thermodynamic integration (TI) methods based on molecular dynamics (MD) simulations are used to determine the per-site segregation free energies of Y at representative GB sites, which show contributions beyond harmonic approximations can be important for certain GB sites at high temperatures. A surrogate model of per-site segregation free energy is constructed from a small set of TI data points using stacking cross-validation regressors and physics-informed descriptors. This model is applied to predict the Y segregation free energy spectra for thousands of GB sites in Mg STGBs with uncertainty quantification. The average segregation tendency predicted by the spectral approach based on the free energy spectra agrees well (within the uncertainty range) with experimental observations for micro-scale polycrystalline Mg alloys at typical thermomechanical processing temperatures (500 ∼ 800 K), where thermodynamic equilibrium states are likely to be achieved due to fast diffusion. [Display omitted] [ABSTRACT FROM AUTHOR]

Closing the gap between experiments and simulations in the investigation of high-pressure silicon phase transitions calls for advanced, new-generation modeling approaches. By exploiting massive parallelization, we here provide molecular dynamics (MD) simulations of Si nanoindentation based on the Gaussian Approximation Potential (GAP). Results are analyzed by exploiting a customized Neural Network Phase Recognition (NN-PR) approach, helping to shed light on the phase transitions occurring during the simulations. Our results show that GAP provides a realistic description of silicon phase transitions. With the support of NN-PR method, the formation mechanism and stability of high-pressure phases are comprehensively studied. Additionally, we also show how simulations based on the less demanding and widely-used Tersoff potential are still useful to investigate the role played by the indenter tip modeling. However, high-pressure phases obtained with GAP are more consistent with observations made in nanoindentation experiments, removing a spurious phase that is shown by Tersoff simulations. This behavior is explained on the base of relative phase stability with comparison with Density Functional Theory (DFT) calculations. This work provides insight into the application of state-of-the-art Machine Learning (ML) methods on nanoindentation simulations, enabling further understanding of the phase transition mechanisms in silicon. [Display omitted] [ABSTRACT FROM AUTHOR]

Using reactive force field molecular dynamics and Density Functional Theory, this study unravels the early stages of TiB 2 oxidation. Overall, it is found that the TiB 2 boron sheets hinder the oxidation until a temperature of 800 K is reached, above which a complex sequence of chemical mechanisms leads to the formation of a titanium oxide at the top surface and agglomeration of pure boron underneath, preventing further TiO 2 growth below 900 K. It is demonstrated that titanium oxidation is possible after the softening and distortion of boron sheets due to oxygen adsorbate presence; mostly BO radicals, no B 2 O 3 -like structure is formed. The local distortions of boron aromatic rings allow oxygen insertion into the subsurface, which is followed by titanium extraction and migration towards the outer surface in contact with the molecular oxygen atmosphere. Mechanistic details of these complex extraction–oxidation processes and their relation to cooperative oxygen atoms and molecules are detailed in terms of pathways and corresponding energetics. Interestingly different reaction stages are identified, that do not exceed 2 eV activation. The proposed hierarchical scenario of oxidation of titanium and boron in TiB 2 might benefit to the general understanding of metal diboride oxidation. [Display omitted] • TiB 2 oxidation is activated at a temperature of 800 K. • TiO 2 forms at the surface under which pure boron is agglomerated. • Boron region forms a barrier to O migration at 900 K hindering oxidation of Ti atoms. • B aromatic rings are distorted by multiple O adsorbates inducing oxidation reaction. • Ti oxidation-extraction sequence is quantified, with ∼ 2-4 eV barriers. [ABSTRACT FROM AUTHOR]

Recent research has highlighted the potential of ferroelectricity in van der Waals bilayers in providing an unconventional route for improving device performance. Understanding the static and dynamic properties of domain wall (DW) is critical unlocking this potential, as key parameters such as switching field and speed heavily rely on them. In this article, we conduct a theoretical exploration of the fundamental properties of textures in stacking-engineered ferroelectrics using a machine-learning potential model. Our results demonstrate that competition between the switching barrier of stable ferroelectric states and in-plane lattice distortion leads to a DW width of ten nanometers. We also demonstrate that DW motion can drastically reduce the critical ferroelectric switching field of a monodomain by two orders of magnitude and enable domain switching on a picosecond timescale, suggesting the potential for ultrafast and energy-saving non-volatile memory devices. Moreover, twisting the bilayer into a stacking Moiré structure results in a super-paraelectric state, because the ferroelectric order is reversibly broken by DW motion already at ultralow electric fields. These findings offer valuable insights into the behavior and properties of stacking-engineered ferroelectrics, with significant implications for the development of next-generation electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Local lattice distortions (LLD) and structural stability of body-centered cubic (bcc) Nb–Ta–Ti–Hf high-entropy alloys (HEAs) are studied as functions of composition employing ab initio density-functional theory calculations, with specific focus on the role of the relative concentrations of group IV (Ti and Hf) versus group V (Nb and Ta) elements. Calculated results are presented as a function of composition x in Nb x Ta 0.25 Ti (0. 75 − x) / 2 Hf (0. 75 − x) / 2 alloys, for elastic moduli, phonon spectral functions, LLD and structural energy differences for the bcc and competing hexagonal close-packed (hcp) and ω phases. The results highlight the important role of group V elements and LLD in stabilizing the bcc structure. They further reveal how composition x can be tuned to alter both the magnitude of the LLD and structural energy differences. Specifically, the magnitude of the structural energy differences, and elastic and dynamic stability of the bcc phase, are enhanced with increasing x , while the LLD increase in magnitude as this concentration is decreased. The results also show evidence of correlated LLD at lower values of x , reflecting local structural distortions towards the ω phase, but not hcp. The degree of ω -collapse is nevertheless partial i.e. , transformation towards this phase is not observed to be complete due to the presence of Ta and Nb. At lower values of x we further find an energy landscape characterized by multiple, nearly degenerate local energy minima for different values of the LLD. [Display omitted] [ABSTRACT FROM AUTHOR]

Twinning plays an important role in governing the balance between strength and ductility in hexagonal-close-packed (HCP) metals. Here, we report a combined experimental and theoretical study of twin nucleation from a single < c + a > dislocation in HCP crystals. Specifically, high-resolution transmission electron microscopy has been used to identify { 11 2 ¯ 1 } twin nuclei in HCP rhenium, providing evidence of their nucleation from a < c + a > dislocation. The favorability of this dislocation-based nucleation mechanism is rationalized by an anisotropic elasticity model of < c + a > dislocation dissociation, parametrized by density functional theory calculations, which suggests the conditions for disconnection nucleation and propagation, under which this { 11 2 ¯ 1 } twinning mechanism is expected to be effective. The analysis serves to advance our understanding of the origin of the unique predominance of { 11 2 ¯ 1 } twinning in rhenium, which correlates with the high strength and ductility featured by this metal. It also provides new insights into design strategies that may be effective in activating this twinning mode and enhancing the balance between strength and ductility in HCP alloys more broadly. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The precipitation of hydrides phases is known to be a source of embrittlement in zirconium and its alloys. In the present work, the effects of hydrogen (H) in the bulk of Zirconium (Zr) systems has been investigated using density functional theory (DFT). A model for the nucleation of hydrides in terms of the thermodynamic and strain conditions has been determined from the examination of interstitial H configurations in hcp-Zr (α -Zr). We found that several coherent hcp structures for Zr 2 H have similar formation energies and structural properties, and thus are relatively easy to form. A number of Zr 2 H hydrides with hcp structures were found to be dynamically unstable, and were found to promote a phase transformation to the fcc lattice. Based on the hydrogen distribution, the orientation relationship and the strain conditions, the transition of Zr 2 H hydrides from the hexagonal to cubic phases have been determined. Our results suggest that hydrogen plays a fundamental role, since a substantial rearrangement is required to promote the hcp → fcc transformation of hydrides phases. We determined that a hcp → fcc transformation of the Zr host lattice is assisted by the lower barrier for phase transition in Zr 2 H compared to that of pure α -Zr. Thus, leading to the formation of the brittle δ hydride phase. The reported formation mechanisms of hydrides provide the basis to understand the precipitation of hydrides observed experimentally. [ABSTRACT FROM AUTHOR]

Fast ionic transportation is in high demand for developing low-temperature solid oxide fuel cells (LT-SOFCs). Facing this challenge, a new H+/O2−/Li+ triple conductor is designed in this study from a lithium-metal oxide, spinel Li 4 Ti 5 O 12 (LTO). First-principle calculation based on density functional theory (DFT) reveals the proton transport barrier in LTO can be as low as 0.37 eV while the barrier for oxygen ion transportation is 0.94 eV. Using the designed LTO as the electrolyte and a typical cathode of lithium-ion battery, LiNi 0.8 Co 0.15 Al 0.05 O 2-δ , as the symmetrical electrodes, an all-lithium-metal-oxides-based LT-SOFC is constructed. High performance is achieved by the SOFC at 550–425 °C, i.e. 625 mW cm−2 at 550 °C, and a low activation energy of 0.60 eV is found with respect to the ionic conductivity of LTO at 550–475 °C. Further study confirms the dual O2−/H+ conduction of LTO via the application of proton and oxygen ion filters as well as the transference number test. Additionally, particular attentions are paid to the transport behavior of Li+ in the cell via a charging process study and from XRD results. The possible contribution of triple conduction on fuel cell performance is discussed. This work demonstrates the great promise of triple H+/O2−/Li+ conducting lithium-metal oxides for LT-SOFC electrolyte development. [Display omitted] [ABSTRACT FROM AUTHOR]

Transition metal oxides exhibit fascinating physical phenomena and hold potential for next-generation electronic devices; therefore, fundamental understanding of their conduction mechanisms is of prime technological importance. We investigate charge transport kinetics and elastic behavior of bulk polycrystalline Ca 2-x R x MnO 4 oxides, where R = Y or La and 0.01 ≤ x ≤ 0.20. Analysis of temperature dependent electronic transport properties considering the nearest neighbor small polaron hopping model in combination with first-principles calculations of elastic properties indicates tight correlation between charge transport and lattice elasticity. We find that the polaron hopping energies of Y-doped compounds are lower than their La-doped counterparts, and attain minimum values of 60 and 73 meV, respectively. This is associated to softening of interatomic bonds, which is more pronounced for Y-doping compared to La-doping. This is corroborated by a fundamental model for elastically isotropic materials, indicating that the elastic energy induced by small polarons corresponds with the measured polaron hopping energies. Accordingly, the lattice shear and Young moduli, sound velocities and Debye temperatures calculated for Y-doped cells are smaller than for La-doped ones. The non-monotonous dependence of hopping energies on dopant concentration is explained in terms of polaron-polaron separation and mutual electrostatic interactions across the Mn+3-O-Mn+4 conduction path. Our study shows how charge carrier dynamics are strongly coupled with elastic properties, implying that the latter can be used to predict charge carrier mobility in oxide semiconductors. [Display omitted] [ABSTRACT FROM AUTHOR]

Regarding hydrogen embrittlement (HE) in the mixtures of hydrogen and inert gas, the results were understood mainly based on the partial hydrogen gas pressure. On the other hand, the effect of the total gas pressure has not been fully investigated. In this study, fatigue crack growth rate (FCGR) tests were conducted in high-purity hydrogen gas at different gas pressures. Also, the FCGR tests were conducted in hydrogen and nitrogen mixtures at different total gas pressures. The hydrogen partial pressure in the mixture was the same as the high-purity hydrogen. This was the first time that acceleration of the FCGR in the mixtures compared to that in the high-purity hydrogen was observed. To elucidate the mechanism of the enhanced HE in the mixtures, hydrogen permeation and hydrogen desorption experiments were carried out. Based on the results of these tests, the acceleration of the FCGR in the mixtures could be interpreted by the fast hydrogen entry rate, which may result in a higher local hydrogen concentration near the crack tip during a limited time. Density functional theory (DFT) calculations were performed to consider the total gas pressure effect on an atomic scale. The thrust force of other gas molecules in the mixtures made the hydrogen molecules enter the potential field of the iron surface sooner, advancing the dissociation of the hydrogen. This will increase the surface concentration of the hydrogen atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

The Al-doped modification strategy by substituting Al for different transition metal ions (TMs, TM = Mn, Ni, Co) has achieved excellent results in improving the cyclic performance of Li-rich Mn-based cathode materials (LRMs). However, the traditional explanation known as "pegging effect" is hard to distinguish how Al works in different TM substitutions. Herein, the electrochemical performances of Li 1.2 Mn 0.52 Ni 0.13 Co 0.13 Al 0.02 O 2 (LRM-Mn), Li 1.2 Mn 0.54 Ni 0.11 Co 0.13 Al 0.02 O 2 (LRM-Ni) and Li 1.2 Mn 0.54 Ni 0.13 Co 0.11 Al 0.02 O 2 (LRM-Co) are studied, and LRM-Mn shows the superior long-term cycling stability, especially at the high temperature of 55 °C. Density functional theory (DFT) reveals that LRM-Mn crystal structure has higher thermodynamic stability than any other sample, which is advantageous for inhibiting the transition of LRMs to low-energy stable phases during cycling (e.g., spinel phase and rock salt phase). Combined with density of states and Bader charge analyses, we think that the increased thermodynamic stability of LRM-Mn results from the reduction of the charge transfer of Mn and Co ions in a single delithiation process, which lowers the reactivity of TMs, alleviates the Li/TM mixing and inhibits the irreversible oxygen release. In addition, the biggest volume change during the delithiation process was observed when Al was substituted for Co, which results in the materials' premature production of fatigue stresses and intergranular cracking. This work comprehensively explains the modification mechanism of Al-doped in LRMs. It demonstrates practical significance for both the rational design of materials and the electrode electrochemical performance prediction. [Display omitted] [ABSTRACT FROM AUTHOR]

The non-linear threshold-type current-voltage behavior that characterizes selector devices for three-dimensional (3D) crossbar-type nonvolatile memory devices relies upon a phenomenon known as Ovonic threshold switching (OTS). Because current practical OTS materials are based on toxic elements, such as Se and As, Te-based OTS materials are expected to offer a more environmentally friendly option. However, the electronic structure that determines the OTS behavior of Te-based OTS materials is not well understood. In this paper, the electronic structure of amorphous Si 0.29 Te 0.71 , has been explored using hard X-ray photoelectron spectroscopy (HAXPES) in conjunction with density functional theory (DFT) calculations. The HAXPES results show that the Si 0.29 Te 0.71 amorphous network of the simulated amorphous structure is based upon Te-Te, Te-Si, and Si-Si bonding. DFT calculations revealed that Si3p and Te5p states contribute to bonding, whereas occupied non-bonding Te5p states form the top of the valence state. A projected local density of states analysis shows that the Si site forms conduction-tail states, whereas the Te site forms both conduction- and valence-tail states. Furthermore, Te-Te dimers contribute significantly to the midgap states that characterize the OTS behavior. Finally, the valence-tail state extension within the mobility gap of Si 0.29 Te 0.71 was experimentally demonstrated. [Display omitted] [ABSTRACT FROM AUTHOR]

Sn-based anodes are potential replacements for commercial carbon-based lithium-ion battery anodes. Moreover, alloying with Cu improves the cyclability of Sn. This study directly grows Cu 6 Sn 5 crystals on polycrystalline Cu current collectors via a solid-liquid reaction with molten Sn alloys. The Cu 6 Sn 5 crystals grown when a molten Sn-Cu alloy was used have a preferred orientation along the η -Cu 6 Sn 5 (101). In this study, the crystals are tailored to grow along the η -Cu 6 Sn 5 (2-12) preferred orientation by excluding Cu in the molten Sn alloy used as a starting material. The (2-12) oriented electrodes show significantly improved electrochemical properties, displaying a 50th cycle discharge capacity of 762 mAh g-1, a 55% increase over the (101) electrode under the same cycling conditions. The (101) electrode ceased to function at 1C and above, while the (2-12) electrode retained around 480 mAh g-1 at 2C. In addition, the (101) electrode shows the formation of 3-fold superstructures in the crystal lattice; while the (2-12) electrode shows atomic arrangements of a higher crystal symmetry, further facilitating the transportation of Li-ions. Density functional theory calculations confirm that Li-ions prefer to adsorb onto Sn in η -Cu 6 Sn 5 and diffuse through the structure in a zig-zag pattern along the [111] channels with a low barrier energy of 0.705 eV. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Individual grains of chalcopyrite solar cell absorbers can facet in different crystallographic directions at their surfaces. To gain a deeper understanding of the junction formation in these devices, we correlate variations in the surface facet orientation with the defect electronic properties. We use a combined analytical approach based on scanning tunneling spectroscopy (STS), scanning electron microscopy, and electron back scatter diffraction (EBSD), where we perform these experiments on identical surface areas as small as 2 × 2 µm2 with a lateral resolution well below 50 nm. The topography of the absorber surfaces indicates two main morphological features: micro-faceted, long basalt-like columns and their short nano-faceted terminations. Our STS results reveal that the long columns exhibit spectral signatures typical for the presence of pronounced oxidation-induced surface dipoles in conjunction with an increased density of electronic defect levels. In contrast, the nano-faceted terminations of the basalt-like columns are largely passivated in terms of electronic defect levels within the band gap region. Corresponding crystallographic data based on EBSD experiments show that the surface of the basalt-like columns can be assigned to intrinsically polar facet orientations, while the passivated terminations are assigned to non-polar planes. Ab-initio calculations suggest that the polar surfaces are more prone to oxidation and resulting O-induced defects, in comparison to non-polar planes. Our results emphasize the correlation between morphology, surface facet orientations and surface electronic properties. Furthermore, this work aids in gaining a fundamental understanding of oxidation induced lateral inhomogeneities in view of the p-n junction formation in chalcopyrite thin-film solar cells. [ABSTRACT FROM AUTHOR]

Strikingly challenging the widely accepted opinion that a giant spontaneous polarization (Ps) of ~150 μC/cm2 in pure BiFeO3 can only be achieved in strain-induced tetragonal(-like) thin films up to a few hundred nm thick, rhombohedral-like, (110)-oriented BiFeO3 thick films (~2 μm) sputter-deposited at 500°C and 450°C exhibit giant Ps values of 152 μC/cm2 and 126 μC/cm2, respectively. Using a thermodynamic computation based on the Landau-Ginzburg-Devonshire potential (LGD) and a density functional theory (DFT) calculation, the enhanced ferroelectric polarization can be qualitatively explained by a (110) growth-orientation and a moderate compressive strain (~ -1.3%). While the (110)-orientation gives a boost in electric polarization by a ratio of ~ 2 as compared to that of (100), and an enhanced piezoelectric response with respect to that of (111), the compressive strain, which is due to a low deposition temperature on Si, further improves the electric polarization and the related piezoelectric response. The resulting large piezoelectric d33 coefficient of ~120 pm/V in the 500°C-deposited film is well correlated with its giant Ps. This work demonstrates how to achieve a large ferroelectric polarization and a high piezoelectric coefficient in bulk-like BiFeO3 films on Si, implying a great potential of this lead-free multiferroic for applications in Si-based integrated devices. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The stability of constituent phases in multi-component system always plays a prominent role in tailoring their mechanical performance at elevated temperatures. In this work, we highlight a chemical ordering feature in the AlTiVCr 1- x Nb x (0 ≤ x ≤ 1) alloys with body-centered cubic crystal structure. The quantum-mechanical first-principle investigations of these alloys on the elemental distribution identify a family of B2 type of partially ordered configurations. We map out the elastic parameters in detail as a function of composition and temperature for disordered and partially ordered phases. A great sensitivity to the order-disorder transformation is revealed, especially for the Cr-rich system. Our results demonstrate that a proper control of the ordering level in these alloys can facilitate the optimal tuning of their mechanical performance while keeping the density almost unchanged. The study presented here further predicts that these alloys possess high specific stiffness, low thermal expansion, and large elastic softening resistance. It is demonstrated that the considered alloys have thermal and mechanical properties that compete with superalloys and other high temperature structural materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

For the past decade, considerable research effort has been devoted toward computationally identifying and experimentally verifying single phase, high-entropy systems. However, predicting the resultant crystal structure(s) "in silico" remains a major challenge. Previous studies have primarily used density functional theory to obtain correlated parameters and fit them to existing data, but this is impractical given the extensive regions of unexplored composition space and considerable computational cost. A rapidly developing area of materials science is the application of machine learning to accelerate materials discovery and reduce computational and experimental costs. Machine learning has inherent advantages over traditional modeling, owing to its flexibility as new data becomes available and its rapid ability to construct relationships between input data and target outputs. In this article, we propose a novel high-throughput approach, called "ML-HEA", for coupling thermodynamic and chemical features with a random forest machine learning model for predicting the solid solution forming ability. The model can be a primary tool or integrated into existing alloy discovery workflows. The ML-HEA method is validated by comparing the results with reliable experimental data for binary, ternary, quaternary, and quinary systems. Comparison to other modeling approaches, including CALPHAD and the LTVC model, are also made to assess the performance of the machine learning model on labeled and unlabeled data. The uncertainty of the model in predicting the resultant phase of each composition is explored via the output of individual predictor trees. Importantly, the developed model can be immediately applied to explore material space in an unconstrained manner, and is readily updated to reflect the results of new experiments. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The HfO 2 -based ferroelectrics have aroused considerable attention due to their potential application in silicon process-compatible memory devices. However, the ferroelectricity origin and the domain evolution have not yet been well understood. It is now generally accepted the orthorhombic Pca 2 1 phase is one of ferroelectric phases for HfO 2. In this work, by performing density functional theory calculations, we systematically studied the domain wall structures and evolution based on the Pca 2 1 ferroelectric phase. More specifically, the atomic structures of ten types of possible 180° and 90° ferroelectric domain walls are predicted and explored. And the motion of certain domain walls is expected as the microscopic mechanisms of the polarization switching and ferroelectricity activation of Pca 2 1 HfO 2 under external electric field. Our results are in good agreement with the recent experimental results on ferroelectric domain walls in HfO 2 -based epitaxial thin-film and are helpful to understand the ferroelectricity origin of the HfO 2 -based ferroelectrics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Achieving efficient and stable ultraviolet emission is a challenging goal in optoelectronic devices. Herein, we investigate the UV luminescence of zinc germanate Zn 2 GeO 4 microwires by means of photoluminescence measurements as a function of temperature and excitation conditions. The emitted UV light is composed of two bands (a broad one and a narrow one) associated with the native defects structure. In addition, with the aid of density functional theory (DFT) calculations, the energy positions of the electronic levels related to native defects in Zn 2 GeO 4 have been calculated. In particular, our results support that zinc interstitials are the responsible for the narrow UV band, which is, in turn, split into two components with different temperature dependence behaviour. The origin of the two components is explained on the basis of the particular location of Zn i in the lattice and agrees with DFT calculations. Furthermore, a kinetic luminescence model is proposed to ascertain the temperature evolution of this UV emission. These results pave the way to exploit defect engineering in achieving functional optoelectronic devices to operate in the UV region. [ABSTRACT FROM AUTHOR]

Weberite-type oxides are a family of oxides with A 3 BO 7 stoichiometry that can adopt different space groups depending on chemical composition. There is a discrepancy in previous studies as to whether Y 3 TaO 7 is the orthorhombic C222 1 or the Ccmm space group. Here, we describe the short- and long-range structural properties of weberite-type Y 3 TaO 7 using neutron total scattering data, which has a high sensitivity to the oxygen sublattice. Simultaneous analysis of both short- and long-range structural data via conventional Rietveld and small box modeling demonstrates that Y 3 TaO 7 is best modeled as C222 1. While the Ccmm describes equally well the long-range structure, pair distribution function analysis revealed that the local atomic configuration can be best modelled as C222 1. This is corroborated by first-principles calculations that confirm the energetic preference of the C222 1 over Ccmm. Neutron total scattering data are reported for the first time for the Y 3 TaO 7 weberite-type ceramics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Metastable transition metal aluminum nitride (TMAlN, TM = Ti, V) thin films are today deposited utilizing ionized vapor phase condensation techniques where variations in ion flux and ion energy cause compressive film stress, in turn affecting Al solubility. While the metastable phase formation of TiAlN has been modeled, the influence of film stresses on phase formation has so far been overlooked. Using combinatorial deposition via magnetron sputtering, thermodynamic modeling and density functional theory calculations, we investigated the phase formation of V 1−x Al x N and Ti 1−x Al x N thin films at various substrate temperatures and deposition rates. Ab initio calculations indicate that the maximum solid solubility of Al in face-centered cubic (fcc) V 1−x Al x N or fcc -Ti 1−x Al x N shows a linear trend as a function of the magnitude of compressive stress. Here, we consider the influence of film stresses on the metastable phase formation of fcc -V 1−x Al x N and fcc -Ti 1−x Al x N for the first time. Specifically, experimental data from a single combinatorial deposition is utilized to predict the stress-dependent formation of metastable phases based on thermodynamic and ab initio data. Explicit consideration of stress extends the Al solubility limit to higher values for both Ti 1-x Al x N and V 1-x Al x N thin films, previously unobtainable by energetics, but accessible experimentally. These predictions are experimentally verified and thus provide guidance for experimental efforts with the goal of increasing the Al concentration in fcc -TMAlN thin films. Image, graphical abstract [ABSTRACT FROM AUTHOR]