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A compositionally tunable series of AuCu films is active for electrocatalytic urea generation from carbon dioxide and nitrate.
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Anode-free solid-state Li batteries promise significant increases in energy densities compared to current commercial batteries that rely on liquid electrolytes. Major challenges persist in controlling morphological evolution during the plating and stripping of lithium metal at the anode current collector. Elemental additives that alloy with lithium have been found to modify the plating and stripping behavior of lithium. Many alloying elements form intermetallics with lithium and the mobility of Li through these intermetallics is believed to have an important effect on morphological evolution. This study shows that Li transport coefficients through intermetallics span a wide range in values, with the B32 LiAl intermetallic predicted to have a Li tracer diffusion coefficient as high as 10 –6 cm 2 /s at room temperature, which is 8 orders of magnitude larger than that of isostructural B32 LiZn. This work demonstrates the crucial role of vacancy concentration in controlling the mobility of Li atoms through intermetallics. While the migration barriers for Li-vacancy exchanges in both LiAl and LiZn are remarkably low, the superatomic conductivity in LiAl is shown to arise from the unique electronic structure of the B32 LiAl compound, which favors high concentrations of vacancies.
Intermetallic compounds (IMCs) are attractive platforms for elucidating structure−catalysis relationships due to their ordered atomic structure and well-defined bulk composition. Yet, how their surfaces reconstruct under reaction conditions and how such reconstruction is governed by bulk stoichiometry remain poorly understood. Here, we show that SiO2-supported Ni−In IMCs undergo reaction-driven surface reconstruction during CO2 hydrogenation and that bulk stoichiometry can be used to steer this evolution toward methanol formation. Among the compositions examined (Ni2In1, Ni1In1, Ni2In3, and Ni1In2), Ni2In3/SiO2 exhibits the highest methanol selectivity (∼70%) and a methanol space-time yield of 652 mg·gmetal−1·h−1 at 250 °C and 30 bar. Combined structural, surface characterization, and kinetic analyses suggest that the intermetallic bulk remains largely preserved, whereas the surface departs from the stoichiometric bulk and evolves toward InOx-enriched surface domains coupled to an electron-rich Ni−In intermetallic phase. The extent of this evolution depends strongly on the bulk Ni:In stoichiometry and is most pronounced for Ni2In3/SiO2. These findings identify bulk stoichiometry as a handle for tuning the working-state surface of intermetallic catalysts and provide a basis for designing methanol synthesis catalysts through controlled surface reconstruction.
The present conference on high-temperature ordered intermetallic alloys discusses alloy theory and phase stability, defects and microstructures, mechanical behavior, alloy design and material processing, multiphase and composite materials, nickel aluminides, titanium aluminides, and other ordered intermetallics. Attention is given to compositional effects on processing and properties of nickel aluminides, dynamic compaction and hot-isostatic-pressing of nickel aluminides, improvement of elevated-temperature material properties in Ni3Al, the effect of microalloying B on the high-temperature mechanical properties of Ti3Al, the effects of structure on creep of Ti-53.4 mol pct Al intermetallics, the deformation microstructure in Ni3Si polycrystals strained over the range of temperature of flow stress anomaly, and the microstructure and mechanical properties of dual phase alloys consisting of the intermetallic phases.
The present volume on intermetallic matrix composites discusses the modeling, processing, microstructure/property relationships, and compatibility of intermetallic matrix composites. Attention is given to models for the strength of ductile matrix composites, innovative processing techniques for intermetallic matrix composites, ductile phase toughening of brittle intermetallics, and reactive synthesis of NbAl3 matrix composites. Topics addressed include solidification processing of NbCr2 alloys, Ta and Nb reinforced MoSi2, the microstructure and mechanical behavior of Ni3Al-matrix composites, and ductile-phase toughening of Cr3Si with chromium. Also discussed are dislocation morphologies in TiB2/NiAl, the development of highly impact resistant NiAl matrix composites, the effect of notches on the fatigue life of the SCS-6Ti3Al composite, and the chemical stability of fiber-metal matrix composites.
The metallurgy and materials communities have long understood and exploited fundamental links between chemical and structural ordering in metallic solids to tailor their mechanical properties. We extend these ideas to include prediction of the nanocrystalline strength limit in high-entropy alloys and intermetallic compounds, where a breakdown occurs in the classical Hall-Petch strengthening behavior. The highest reported strength achievable through alloying has rapidly climbed and given rise to new classifications of materials with extraordinary properties, with a notable case being nanocrystalline metals. High-entropy alloys (chemically disordered, concentrated solid solutions) and intermetallic compounds are two boundary cases of how tailored order can be used to manipulate mechanical behavior. Here, we show that the complex electronic-structure mechanisms governing the peak strength of alloys and pure metals can be reduced to a few physically meaningful parameters based on their atomic arrangements and used – with no fitting parameters – to predict the maximum strength of these materials. This includes a generalized energy-based accounting for the degree of structural and chemical ordering that allows for rapid and reasonably accurate prediction of peak strength (validated in the nanocrystalline limit) as a function of temperature. Predictions of maximum strength based on the activation energy (with all materials properties derived from DFT calculations or experiments) for a stress-driven transition to an amorphous state is shown to accurately describe the breakdown in Hall-Petch behavior at the smallest crystallite sizes for pure metals, intermetallic compounds, high-entropy alloys, and metallic glasses. Further, this activation energy is also shown to be directly proportional to interstitial electronic charge density, which is a good predictor of ductility, stiffness (moduli), and phase stability in high-entropy alloys and solid metals generally. The proposed framework suggests the possibility of coupling ordering and intrinsic strength to mechanisms like dislocation nucleation, hydrogen embrittlement, and transport properties, such as through correlations between the activation energies for amorphization with stacking-fault and grain boundary energies. It additionally opens the prospect for greatly accelerated structural materials design and development to address materials challenges limiting more sustainable and efficient use of energy.
Intermetallic compounds serve as model catalysts for selective hydrogenation reactions, offering precise control over the active site composition(s), geometric and electronic structure. The addition of a third element to form a ternary intermetallic alters the exposed crystal facet(s), demonstrating a strategy to impart improved catalytic behavior in intermetallic catalysts. The site-specific substitution of a small fraction of Pd atoms with Au in pyrite-type PdSb 2 results in the preferential exposure of the (100) facet over the (111) facet. Electron back scattered diffraction and density functional theory calculations confirm the facet change upon the substitution of Pd with Au to form the ternary Pd 1−x Au x Sb 2 (0.075 ≤ x ≤ 0.25). The (100) facet demonstrates higher net alkene selectivity due to significantly weaker alkene binding compared to the (111) facet. Distinct from our prior work on chemical substitution to directly alter the active site composition, this work demonstrates the indirect modification of active sites via preferential facet exposure.
We present a descriptor based on charge-induced atomic strain in crystalline lattices for predicting structural phase transformations in rare-earth intermetallic compounds containing lanthanides and transition metals. The charge-induced local atomic strain was obtained from structural optimization of experimentally known crystalline phases using state of the art density-functional theory methods. The predictive power of the descriptor was evaluated on 𝑅𝐸 2 In (𝑅𝐸 = rare earth) compounds, a class known for diverse phase transformations. We show that incorporating quantum-mechanical effects—such as local charge distribution, bonding, symmetry, and electronic structure—enhances the robustness of the descriptor. To gain further insight, we analyzed phononic and electronic behavior in Y 2 In and demonstrated that experimental phase transformations are captured only when atomic strain effects are included. The descriptor was further used to predict structural phase changes in (Yb 1–𝑥 Er 𝑥 ) 2 In and Gd 2 (In 1–𝑥 Al 𝑥 ), with predictions confirmed by x-ray powder diffraction. Here, while the current study is focused on lanthanide-based intermetallics, the underlying principles of the descriptor suggest potential applicability to other closely related classes of rare-earth intermetallics.
Metal dissolution, nanoparticle agglomeration, and carbon support corrosion cause significant performance degradation of current PtCo catalysts under acidic and oxidative oxygen reduction reaction. Here, in this study, an integrated strategy is presented to design high-performance Pt 3 Co intermetallic catalysts by regulating gaseous Co deposition-driven diffusion into Pt nanoparticles supported on a composite carbon. The composite carbon is derived from ZIF-8/polyaniline, consisting of a high-surface-area (HSC) core and a protective graphitic shell (GS), which is employed to design 40 wt.% Pt/HSC@GS catalyst. The corresponding membrane electrode assemblies (MEAs) can maintain 1.09 A cm −2 at 0.7 V (20. 7% loss) after 10 000 cycles (1.0–1.5 V for carbon stability) and 1.15 A cm −2 (16.1% loss) after 150 000 cycles (0.60–0.95 V for catalyst stability). A ordered Pt 3 Co intermetallic is synthesized via a gaseous Co-deposition process, which yields a homogeneous Co-rich layer onto the Pt nanoparticles on the composite support, thereby facilitating Co diffusion into Pt crystal during subsequent ordering annealing to form the ordered intermetallic structure. This gaseous deposition leads to a thin carbon layer on PtCo nanoparticles, inhibiting particle growth during the annealing and mitigating Co dissolution under dynamic electrochemical conditions. The PtCo catalyst achieves impressive MEA performance and long-term durability (1.45 A cm −2 at 0.7 V after 120 000 cycles) under heavy-duty conditions.
Interest in metastable β-Ti has grown, due to the exceptional work hardening caused by TRansformation and TWinning Induced Plasticity (TRIP/TWIP). A current challenge is increasing the yield strength, while maintaining the benefits of TRIP/TWIP. This study presents the first report of TRIP/TWIP in a metastable β-Ti alloy containing intermetallic compounds, specifically Ti silicide precipitates. Silicon (Si) additions enable the formation of silicide particles, which can be precipitated, dissolved, and controlled through tailored heat treatments. In-situ synchrotron x-ray diffraction during tensile testing reveals primary {332}<113> twinning activates first, followed by TRIP, leading to extensive work hardening and uniform elongation in the solutionized state. In conclusion, these findings open a novel microstructural approach to the design of multiphase TRIP/TWIP titanium alloys, relying on intermetallic precipitation rather than allotropes such as α or ω phase, and lay the groundwork for future studies on intermetallic precipitation strengthening.
The strain effect of high-entropy intermetallic (HEI) catalysts on oxygen reduction reaction (ORR) performance remains largely unexplored, primarily due to the significant challenges associated with characterizing and calculating the intricate local coordination environments. Here, we design a nitrogen (N)-doped L1 0 -ordered PtCoNiFeCu intermetallic catalyst supported on Ketjenblack carbon (N-HEI/KB), and reveal the origin of the sub-angstrom strain in N-HEI and its impact on ORR performance by combining atomic-scale characterization and theoretical calculations. The synergistic interplay of the sub-angstrom strain, the pinning effect of metal-N bonds, and the high-entropy effect contribute to the competitive stability of N-HEI/KB catalysts, providing high current density of 1388 mA cm -2 at 0.7 V after 90,000 cycles even under harsh heavy-duty vehicle conditions. These findings broaden the avenues for designing high-performance high-entropy intermetallic cathode electrocatalysts.
Intermetallic compounds are widely recognized for their high-temperature phase stability and resistance to composition and structural changes. However, we reveal athermally activated bulk-to-surface mass exchange mechanism that drives surface phase separation, resulting in the formation of surface precipitates with distinct composition andstructure from the bulk matrix. Using the archetypal β-NiAl system, we show that asymmetries in vacancy formation energies between Ni and Al atoms induce preferential Ni segregation to the surface, forming Ni-rich γ'-Ni 3 Al precipitates. By integrating in-situ electron microscopy, synchrotron X-ray absorption spectroscopy and first-principles computational modeling, we establish a direct mechanistic connection between bulk thermal defect dynamics, surface compositional evolution, and phase segregation behavior. This bulk-surface coupling mechanism can be a driver of surface phase separation in multicomponent alloys under thermal stress. In conclusion, these results refine the thermodynamic boundaries of intermetallic stability and provide insights into managingthe performance and durability of intermetallic alloys for demanding high-temperature applications.
Lanthanide-containing materials are of interest because of their useful magnetic and electronic behavior. To study this intrinsic behavior, researchers need high-quality single crystals to avoid interference from grain boundaries or defects commonly found in polycrystalline samples. One method for growing single crystals is metal-flux synthesis, an approach that promotes crystal growth at lower reaction temperatures thus providing access to complex intermetallic phases. My project focuses on synthesizing novel lanthanide-containing intermetallic silicides related to previously reported f-element compounds with the Gd1??Fe4Si10?? structure type. I investigated reactions targeting lanthanum, praseodymium, neodymium, samarium, europium, and gadolinium-containing products, and used scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) to identify promising lanthanide-containing phases. I prepared reactions by loading lanthanide oxides, Co, Si, Al, and Ga into alumina crucibles in a 0.2:1:1:10:10 Ln2O3/Co/Si/Al/Ga mmol ratio, where Ln = La, Nd, Pr, Sm, Eu, or Gd. The reactions were sealed in quartz tubes, heated in a furnace, and centrifuged to separate crystals from excess flux. Afterwards, I mechanically isolated single crystals and prepared them for characterization. Pr-, Nd-, and Sm-containing reactions were confirmed through SEM-EDS to have formed the targeted quaternary phase. Single crystal X-ray diffraction (SC-XRD) data showed the Nd-containing crystals exhibited a hexagonal unit cell associated with the Gd1??Fe4Si10?? structure type. La- and Eu-containing reactions instead formed competing Co(Al/Ga/Si)3 phase crystals. Single-crystal XRD, powder XRD, and magnetic susceptibility and heat-capacity measurements will be collected for the remaining lanthanide-containing crystals. This data will help determine the complete crystal structure of the lanthanide analogues, their phase purity and whether they exhibit localized magnetic behavior, magnetic ordering, or other electronic signatures that can be compared with the previously reported actinide analogues. The disordered structure of this intermetallic family is associated with unusual magnetic and electronic behavior meaning lanthanide analogues may show potential as thermoelectric materials. Developing new thermoelectric candidate materials is relevant to energy efficiency and waste-heat recovery, which supports DOE’s broader goal of advancing science and technology solutions for America’s energy needs.
The papers presented in this volume provide on overview of recent theoretical and experimental research in the field of high-temperature ordered intermetallic alloys. The papers are gouped under the following headings: ordering behavior and theory, microstructures, mechanical behavior, alloy design and microstructural control, and metallurgical properties. Specific topics discussed include antiphase domains, disordered films and the ductility of ordered alloys based on Ni3Al; kinetics and mechanics of formation of Al-Ni intermetallics; deformability improvements of L1(2)-type intermetallic compounds; B2 aluminides for high-temperature applications; and rapidly solidified binary TiAl alloys.
Laser surface remelting of as-cast Al-Ge eutectic alloy is shown to produce ultrafine lamellar eutectic morphology with interlamellar spacing refined up to ∼60 nm and composed of FCC Al solid solution and unusual Al x Ge y intermetallic phases that do not form during near-equilibrium solidification. The microstructures are characterized and analyzed using a combination of selected area electron diffraction, high-resolution scanning transmission electron microscopy, energy dispersive X-ray spectroscopy to obtain high-resolution elemental maps, and atomistic modeling using density functional theory followed by atomic-scale image simulation. Depending on the local solidification conditions, the crystallography of the Al x Ge y intermetallic phases in the eutectic microstructure is either monoclinic (C 2/c) or monoclinic (P 2 1 ), with high densities of defects in both cases. This is in sharp contrast to the as-cast alloys that showed nominally pure Al and Ge phases with significant solute partitioning and equilibrium FCC and diamond cubic crystal structures, respectively. Corresponding kinetic phase diagrams are proposed to interpret the evolution of nano-lamellar eutectic morphologies with equilibrium Al and metastable Al x Ge y phases, and to explain increased solid solubility in the Al phases manifested by precipitation of ultrafine clusters of Ge. Furthermore, the reasons for the formation of these metastable eutectics under laser rapid solidification are discussed from the perspective of the competitive growth criterion.
One element of the diversity of intermetallic phases is the formation of complex structures from the assembly of fragments of simpler structures. Recently, we devised the Interface Nuclear Approach as a model for understanding such modular arrangements, in which the intergrowth of different structures is driven by chemical pressure (CP) relief at shared motifs at the domain interfaces, referred to as interface nuclei. In this Article, we present the synthesis, crystal structure, and CP analysis of a new compound that expands on this theme, Y 13 Ag 42.7 Zn 29.7 . Its hexagonal structure contains interpenetrating domains based on the CaPd 5+x and EuMg 5 types. The CaPd 5+x -based regions are reminiscent of the lamellar intergrowth structures previously observed in the Y−Ag−Zn system. In Y 13 Ag 42.7 Zn 29.7 , however, the domains have a different morphology, forming columns that adopt a hexagonal rod-packing. The geometrical features of the remaining spaces are assigned, using the program GrowDomain, to the cores of trigonal units of the EuMg 5 type, while layers of disordered atoms occur at heights along z where the parent structures are mismatched. At the CaPd 5+x -type/EuMg 5 -type interfaces, simple interface nucleus motifs with strong CP-complementarity can be identified, while their distribution within the parent structures supports the notion of templated architectures in modular intermetallics.
Due to their partially filled f-orbitals, lanthanide and actinide intermetallic materials exhibit intriguing electronic, structural, and magnetic properties. These materials provide a unique platform to explore exotic magnetic and quantum phenomena that arise from their strongly correlated f-electrons, offering insights into f-electron behavior. Incorporating light elements such as boron and carbon can significantly impact the electronic, chemical, and physical properties of these materials, with varying influence between lanthanides and actinides due to the more localized f-electrons in lanthanides. In this work, lanthanide-based intermetallic single crystals containing light atoms were synthesized using the molten metal flux growth method. In this method, one or more low-melting metals such as aluminum, gallium, tin, and bismuth are used in excess as the reaction medium. This solution-state approach allows for lower reaction temperatures compared to solid-state reactions and enables the isolation of kinetic products rather than thermodynamically stable compounds. The synthesized crystals were analyzed using an extensive array of analytical and computational characterization techniques, including single crystal X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, magnetization measurements, and density functional theory calculations. These analyses provided detailed insights into the structural and magnetic properties of the synthesized materials.