Search

Single-phase multi-principal element alloys hold promise for improved mechanical properties as a result of multiple operative deformation modes. However, the use of many of these alloys in structural applications is limited as a consequence of their poor aqueous corrosion resistance. Here we introduce a new approach for significantly improving the passivation behavior of alloys by tuning the chemical short-range order parameter. We show that the addition of only 0.03 to 0.06 mole fraction of Al to a (FeCoNi) 0.9 Cr 0.1 alloy changed both the magnitude and sign of the Cr-Cr order parameter resulting in passivation behavior similar to 304L stainless steel containing twice the amount of Cr. Our analysis is based on comparing electrochemical measures of the kinetics of passive film formation with chemical short-range order characterizations using time-of-flight neutron scattering, cluster expansion methods, density functional theory and Monte Carlo techniques. Our findings are interpreted within the framework of a recently proposed percolation theory of passivation that examines how selective dissolution of the non-passivating alloy components and short-range order results in excellent passive films at reduced levels of the passivating component. [Display omitted] [ABSTRACT FROM AUTHOR]

Excellent OER catalysts can enhance the efficiency of hydrogen production from electrolytic water. The development of low-cost, abundant, and highly efficient catalysts remains crucial for the electrolytic hydrogen production industry. In this work, we have developed a highly efficient and cost-effective stainless steel-based OER catalyst using a strategy combining anodic corrosion and structural reconstruction. This approach is not only simple and easy to scale up production, but more importantly, it can also achieve controllable switching of lattice oxygen evolution mechanism (LOM). Specifically, in a 1 M KOH electrolyte, this catalyst achieves current densities of 500 mA/cm² and 1000 mA/cm² with remarkably low overpotentials of only 347 mV and 382 mV, respectively. Moreover, the catalyst exhibits exceptional stability even under high industrial current densities. In-situ differential electrochemical mass spectrometry (DEMS) experiments provide direct evidence of the transition from the adsorbate evolution mechanism (AEM) to the LOM. Through comprehensive characterizations and density functional theory (DFT) calculations, we have elucidated the underlying mechanism responsible for the improved performance and identified key factors influencing the induction of the LOM. This work provides support and new insights for the design and preparation of high-performance steel-based electrolytic water catalysts. In this work, we have developed a highly efficient and cost-effective stainless steel-based OER catalyst using a strategy combining anodic corrosion and structural reconstruction. This approach is not only simple and easy to scale up production, but more importantly, it can also achieve controllable switching of lattice oxygen evolution mechanism (LOM). Our study demonstrates that the SS-AC-SR exhibits remarkable OER performance, with impressively low overpotentials of 229 mV, 347 mV and 382 mV at current densities of 10, 500 and 1000 mA/cm2, respectively, in 1 M KOH. Furthermore, the catalyst demonstrates excellent stability even under high industrial current densities, showcasing its potential for industrial-scale green hydrogen production. [Display omitted] [ABSTRACT FROM AUTHOR]

Chemical short-range order (SRO) is known to alter a wide array of alloy properties. Here, we investigate the SRO of binary and ternary alloys in the Cr–Mo–W system using density functional theory (DFT) calculations, coupled with Monte Carlo simulations and two distinct approaches: the real-space cluster expansion (CE) and a machine learned interatomic potential (MLIP) based on the moment tensor potential (MTP) form. The size-mismatched binary, Cr–W, exhibits phase-separating long-range order (LRO) in the phase diagram, but surprisingly, the SRO is predicted to be ordering-type from both CE and MTP. We rationalize this apparent discrepancy by accounting for the large coherency strain present in this system, which significantly suppresses the coherent phase-separating tendency relative to the incoherent phase diagram. This competition between LRO and SRO persists in the ternary Cr–Mo–W system, where we find that SRO tendencies can qualitatively differ from those in the corresponding binary alloy. The real-space CE can efficiently capture the correct nearest neighbor SRO tendencies in this system, despite failing to account for long-range strain effects, provided it is trained on the energies of sufficiently large structures to capture short-range strain contributions over the nearest neighbor ranges; however, we suggest MTP, or more generally MLIP, may provide a more general approach for comprehensive studies in disordered alloy systems, especially in medium- and high-entropy alloys exhibiting large lattice mismatch. [Display omitted] [ABSTRACT FROM AUTHOR]

Who governs interfacial friction, classical tribology theory or charge-energy evolution theory? Since it was widely recognized that the origin of friction is interatomic forces, attention has gradually shifted towards the characteristics of local nanoscale interfaces. The new theory believes the charge density evolution during the friction process has more significant attributes in determining the interfacial friction. Here, we discuss the frictional failure mechanism at the ceramic/metal interface formed after the nitriding. The increase in N-doped interface friction is supported by classical tribology theory and corresponds to high interface adhesion work. On the other hand, the H-doped interface with the lowest adhesion work exhibits the highest friction. Unlike other interface systems (metallic bonding), the failure interface after H doping is an ionic bonding interface. Stronger ionic bonds are formed and broken in relative sliding, significantly increasing charge density. This emphasizes the crucial role of charge density in this process, aligning with the principles of the new theory. Nevertheless, the classical tribology theory can still be used when measuring interfacial friction of the interface with the same chemical bonds, and it may be more convincing than the new theory. Overall, these research results reveal the intrinsic origin of H/N's influence on TiN/Ti interfacial friction and provide new insights into understanding natural failures at the nanometer level. [Display omitted] [ABSTRACT FROM AUTHOR]

Thermodynamic bulk phase diagrams have become the roadmap used by researchers to identify alloy compositions and process conditions that result in novel materials with tailored properties. Recent experimental studies show that changes in the alloy composition can drive not only transitions in the bulk phases present in a material, but also in the concentration and type of defects they contain. Defect phase diagrams in combination with density functional theory provide a natural route to study these chemically driven defects. Our results reveal, however, that direct application of equilibrium bulk thermodynamics can fail to reproduce experimentally observed defect formation. Therefore, we extend the concept to metastable defect phase diagrams to account for kinetic limitations that prevent the system from reaching equilibrium. We apply this concept to successfully explain the formation of large concentrations of planar defects in supersaturated Fe-Nb solid solutions. We then utilize it to design suitable conditions for synthesis, which we subsequently realized experimentally, successfully validating the formation of the predicted defects in Mg-Al-Ca alloys. The concept offers new avenues for the design of materials performance by tailoring defect structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbide materials find extensive application as tool materials due to their exceptional properties, encompassing high hardness, wear resistance, and robust strength. Exhibiting diverse bonding characteristics, carbides constitute a pivotal material class in modern-day technologies. The structural and energetic attributes of grain boundaries play a vital role in understanding the properties of polycrystalline materials, necessitating an examination of the grain boundary regime. In this study, metal carbide grain boundaries, specifically the Kingery type Σ3 (111) grain boundaries in TiC, TaC, and WC, were systematically investigated utilizing density functional theory calculations. The scrutiny comprehends their structural, electronic, mechanical, and thermal properties. Results show that the investigated grain boundaries are energetically stable. The calculated electronic properties further unveil the presence of metallic behavior. Dynamic stability was observed at 0 K for Σ3 (111) grain boundaries constructed from the L1 0 cubic lattice structure in TiC, while phonon softening was observed for the Σ3 (111) grain boundaries structures in TaC and WC. Thermodynamic properties, including Helmholtz free energy, heat capacity, and entropy, were thoroughly scrutinized. Mechanical properties suggest the ductile behavior with significant metallic nature of considered grain boundary systems. The study extended to thermal properties, examining the lattice thermal conductivity (κ L) of the considered grain boundary systems. It was observed that the Σ3 (111) grain boundary in TiC significantly increases the thermal conductivity. [Display omitted] [ABSTRACT FROM AUTHOR]

The Cluster Expansion (CE) Method encounters significant computational challenges in multicomponent systems due to the computational expense of generating training data through density functional theory (DFT) calculations. This work aims to refine the cluster and structure selection processes to mitigate these challenges. We introduce a novel method that significantly reduces the computational load associated with the calculation of fitting parameters. This method employs a Graph Neural Network (GNN) model, leveraging the M3GNet network, which is trained using a select subset of DFT calculations at each ionic step. The trained surrogate model excels in predicting the volume and energy of the final structure for a relaxation run. By employing this model, we sample thousands of structures and fit a CE model to the energies of these GNN-relaxed structures. This approach, utilizing a large training dataset, effectively reduces the risk of overfitting, yielding a CE model with a root-mean-square error (RMSE) below 10 meV/atom. We validate our method's effectiveness in two test cases: the (Ti, Cr, Zr, Mo, Hf, Ta)B 2 diboride system and the Refractory High-Entropy Alloy (HEA) AlTiZrNbHfTa system. Our findings demonstrate the significant advantages of integrating a GNN model, specifically the M3GNet network, with CE methods for the efficient predictive analysis of chemical ordering in High Entropy Materials. The accelerating capabilities of the hybrid ML-CE approach to investigate the evolution of Short Range Ordering (SRO) in a large number of stoichiometric systems. Finally, we show how it is possible to correlate the strength of chemical ordering to easily accessible alloy parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

[GeTe] m -[Sb 2 Te 3 ] n superlattice (GST-SL) is a promising material candidate to solve the critical problem of high-power consumption for phase-change memory technology. However, the switching mechanism is still under strong debate during the last decade. A key controversial question is that whether melting in GST-SL is possible. In this work, a large-scale machine learning interatomic potential (MLIP) molecular dynamics (MD) simulation with a one-order-of-magnitude larger atom number than that of conventional density functional theory (DFT) MD captures a unique partial melting behavior in GST-SL, where a sparse-nucleation-and-growth governed melting behavior is triggered by the flipping of atoms into van der Waals (vdW) gaps and forming cation-in-vdW-gap (CiV) defect as starting point, and then is slowly developed via propagating liquid-crystalline interfaces. In great contrast, the traditional melting of rock salt (RS)-GST occurs very fast due to instant homogeneous nucleation from high-density intrinsic vacancies distributed randomly in its cubic lattice. Therefore, the melting regions in GST-SL can be spatially localized in form of partial melting and are readily controlled. Moreover, the atomic distribution after melting in GST-SL is more chemical ordering than that in RS-GST. By the large-scale MLIP-MD, the present study provides a critical atomic insight into GST-SL phase-change behaviors that conventional DFT-MDs hardly achieve. This partial-melting nature in GST-SL helps explain the long-term-confused working principle of GST-SL-based phase-change memory, which will accelerate its application in the big-data era. [Display omitted] [ABSTRACT FROM AUTHOR]

The vast chemical space of high entropy alloys (HEAs) makes trial-and-error experimental approaches for materials discovery intractable and often necessitates data-driven and/or first principles computational insights to successfully target materials with desired properties. In the context of materials discovery for hydrogen storage applications, a theoretical prediction-experimental validation approach can vastly accelerate the search for substitution strategies to destabilize high-capacity hydrides based on benchmark HEAs, e.g. TiVNbCr alloys. Here, machine learning predictions, corroborated by density functional theory calculations, predict substantial hydride destabilization with increasing substitution of earth-abundant Fe content in the (TiVNb) 75 Cr 25- x Fe x system. The as-prepared alloys crystallize in a single-phase bcc lattice for limited Fe content x < 7, while larger Fe content favors the formation of a secondary C14 Laves phase intermetallic. Short range order for alloys with x < 7 can be well described by a random distribution of atoms within the bcc lattice without lattice distortion. Hydrogen absorption experiments performed on selected alloys validate the predicted thermodynamic destabilization of the corresponding fcc hydrides and demonstrate promising lifecycle performance through reversible absorption/desorption. This demonstrates the potential of computationally expedited hydride discovery and points to further opportunities for optimizing bcc alloy ↔ fcc hydrides for practical hydrogen storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Short-range order (SRO), the regular and predictable arrangement of atoms over short distances, alters the mechanical properties of technologically relevant structural materials such as medium/high entropy alloys and austenitic stainless steels. In this study, we present a generalized spin cluster expansion (CE) model and show that magnetism is a primary factor influencing the level of SRO present in austenitic Fe–Ni–Cr alloys. The spin CE consists of a chemical cluster expansion combined with an Ising model for Fe–Ni–Cr austenitic alloys. It explicitly accounts for local magnetic exchange interactions, thereby capturing the effects of finite temperature magnetism on SRO. Model parameters are obtained by fitting to a first-principles data set comprising both chemically and magnetically diverse face-centered cubic configurations. The magnitude of the magnetic exchange interactions are found to be comparable to the chemical interactions. Compared to a conventional implicit magnetism CE built from only magnetic ground state configurations, the spin CE shows improved performance on several experimental benchmarks over a broad spectrum of compositions, particularly at higher temperatures due to the explicit treatment of magnetic disorder. We find that SRO is strongly influenced by alloy Cr content, since Cr atoms prefer to align antiferromagnetically with nearest neighbors but become magnetically frustrated with increasing Cr concentration. Using the spin CE, we predict that increasing the Cr concentration in typical austenitic stainless steels promotes the formation of SRO and increases order–disorder transition temperatures. This study underscores the significance of considering magnetic interactions explicitly when exploring the thermodynamic properties of complex transition metal alloys. It also highlights guidelines for customizing SRO through adjustments of alloy composition. [Display omitted] [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) has opened new frontiers for the design of refractory high-entropy alloys (HEAs) for high-temperature applications. The thermal conductivity of the AM feedstock is among the most important thermo-physical properties that control the melting and solidification process. Despite its significance, there remains a notable gap in both computational and experimental research concerning the thermal conductivity of HEAs. Here, we use density functional theory (DFT) to systematically investigate the alloying effects on the transport properties of Ti-Cr-Mo-W-V-Nb-Ta RHEAs, including electrical and thermal conductivities and Seebeck coefficient. The relaxation time of charge carriers is a key underlying parameter determining thermal conductivity that is exceedingly challenging to predict from first principles alone, and we thus follow the approach by Mukherjee, Satsangi, and Singh [ Chem Mater 32, 6507 (2022) ] to optimize the relaxation time for RHEAs. We validated thermal conductivity predictions on elemental solids, binary and ternary alloys, and RHEAs and compared them against thermodynamic (CALPHAD) predictions and our experiments with good correlations. To understand observed trends in thermal conductivity, we assessed the phase stability, electronic structure, phonon, and intrinsic- and tensile strength of down-selected RHEAs. Our electronic structure and phonon results connect well with the observed compositional trends for thermal transport in RHEAs. Our DFT assessment and CALPHAD predictions provide a unique design guide for RHEAs with tailored thermal conductivity, a critical consideration for AM and thermal-management applications. [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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]