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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

The search for high-entropy fuel-cell catalysts using disorder descriptors

The transition to a hydrogen economy depends on efficient, affordable catalysts for fuel cells. Platinum—the industry standard for fuel-cell electrodes—is costly and scarce, highlighting the need for practical alternatives. High-entropy alloys offer vast compositional diversity and tunable properties that can mitigate these issues, yet their chemical complexity and configurational disorder have hindered rational discovery. Here, we introduce a data-driven framework that couples machine learning with first-principles disorder descriptors—including the entropy forming ability, disordered enthalpy-entropy descriptor, and electronic-structure similarity metrics to platinum—to predict alloy synthesizability and catalytic performance. These descriptors are applied for the first time in the context of fuel-cell catalyst discovery. The workflow rapidly screens more than 20 000 compositions and identifies several platinum-free candidates that are economically viable, readily scalable, and exhibit promising predicted activity. These results demonstrate that disorder descriptors are reliably predicted by machine learning models and can be effectively integrated into materials-discovery pipelines, accelerating innovation across complex compositional spaces.

fuel-cell catalysts↗
DOE OSTI2024

Synthesis and symmetry of perovskite oxynitride CaW(O,N) 3

Perovskite oxynitrides, in addition to being promising electrocatalysts and photoabsorbers, present an interesting case study in crystal symmetry. Full or partial ordering of the O and N anions affects global symmetry and influences material performance and functionality; however, anion ordering is challenging to detect experimentally. In this work, we synthesize a novel perovskite oxynitride CaW(O,N) 3 and characterize its crystal structure using both X-ray and neutron diffraction. Through co-refinement of the diffraction patterns with a range of literature and theory-derived model structures, we demonstrate that CaW(O,N) 3 adopts an orthorhombic Pnma average structure and exhibits octahedral distortion with evidence for preferred anion site occupancy. However, through comparison with a large, low-symmetry unit cell, we identify the presence of disorder that is not fully accounted for by the high-symmetry model. We compare CaW(O,N) 3 with SrW(O,N) 3 to demonstrate the broader presence of such disorder and identify contrasting features in the electronic structures. This work signifies an updated perspective on the inherent crystal symmetry present in perovskite oxynitrides.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Tutorial: Defects in topological semimetals

Three-dimensional topological semimetals are a class of electronic materials in which their bulk and surface states contain linear band touching nodes near the Fermi level. Like semiconductors, their properties will be affected by point and extended defects in their crystal structures, although the extent to which defects and disorders influence topological semimetals may differ in key ways due to their unique electronic structures. In this Tutorial, we provide an overview of the defects in topological semimetals, covering both computational and experimental methods for exploring defect-property relationships. We also include a discussion on open questions that still need to be explored further.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ultrafast lattice disordering can be accelerated by electronic collisional forces

In the prevalent picture of ultrafast structural phase transitions, the atomic motion occurs in a slowly varying potential energy surface determined adiabatically by the fast electrons. However, this ignores non-conservative forces caused by electron-lattice collisions, which can significantly influence atomic motion. Most ultrafast techniques only probe the average structure and are less sensitive to random displacements, and therefore do not detect the role played by non-conservative forces in phase transitions. Here we show that the lattice dynamics of the prototypical insulator-to-metal transition of VO 2 cannot be described by a potential energy alone. We use the sample temperature to control the preexisting lattice disorder before ultrafast photoexcitation across the phase transition and our ultrafast diffuse scattering experiments show that the fluctuations characteristic of the rutile metal develop equally fast (120 fs) at initial temperatures of 100 K and 300 K. This indicates that additional non-conservative forces are responsible for the increased lattice disorder. In conclusion, these results highlight the need for more sophisticated descriptions of ultrafast phenomena beyond the Born-Oppenheimer approximation as well as ultrafast probes of spatial fluctuations beyond the average unit cell measured by diffraction.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis and Transport Properties of the Family of Zintl Phases Ca 3 RESb 3 (RE = La–Nd, Sm, Gd–Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance

Zintl phases with complex crystal structures have been studied as promising candidate-materials for thermoelectric (TE) applications. Here, we report the syntheses of the family of rare-earth metal Zintl phases with the general formula Ca 4–x RE x Sb 3 (x ≈ 1; RE = La–Nd, Sm, Gd–Tm, Lu). The structural elucidation is based on refinements of single-crystal X-ray diffraction data for 12 unique chemical compositions. The cubic structure is confirmed as belonging to the anti-Th 3 P 4 structure type (space group I4¯3d, no. 220, Z = 4), where the Ca and RE atoms share the same atomic site with ca. 75% and 25% occupancies, respectively. Such crystallographic disordering of divalent Ca and trivalent RE atoms in the structure provides a pathway to intricate bonding. The latter, together with the presence of heavy elements such as Sb and the lanthanides, are expected to enhance the scattering probability of phonons, thereby leading to as low thermal conductivity κ as that of the ordered RE 4 Sb 3 . The drive of the hypothetical parent compound Ca 4 Sb 3 to be stabilized by alloying with rare-earth metals can be understood following the Zintl-Klemm concept, as the resultant formula may be rationalized as (Ca 2+ ) 3 RE 3+ (Sb 3– ) 3 , indicating the realization of closed-shell electronic configurations for all elements. This notion is confirmed by electronic structure calculations, which reveal narrow bandgaps E g = 0.77 and 0.53 eV for Ca 3 LaSb 3 and Ca 3 LuSb 3 , respectively. Additionally, the incorporation of RE atoms into the structure drives the phase into a state of a degenerate semiconductor with dominant hole charge carriers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermoelectric performance in disordered Cu 2 ZnSnSe 4 nanostructures driven by ultra-low thermal conductivity

Here, high-energy reactive mechanical alloying (ball milling) was used to synthesize tetragonal and cubic polymorphs of Cu 2 ZnSnSe 4 . The ordered tetragonal (I-4) polymorph undergoes a phase transition above 400 K into a Cu-Zn disordered tetragonal (I-42 m) polymorph, while the cubic (F-43 m) polymorph with full cation disorder is stabilized at room temperature. Both polymorphs show ultra-low thermal conductivities, 0.42 W m -1 K -1 at 722 K and 0.21 W m -1 K -1 at 523 K for the disordered tetragonal and cubic phases respectively. The cubic polymorph has a higher zT in the low-temperature range, peaking at 0.26 (523 K), while the disordered tetragonal has a maximum zT of 0.46 at 712 K. The latter is the highest reported zT for stoichiometric Cu 2 ZnSnSe 4 , comparable to the best-performing doped materials in the literature. A combination of experimental results and ab-initio calculations point to a coupling between structural disorder and microstructure as the mechanism behind the reported performance.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Beyond Conventional Charge Density Wave for Strongly Enhanced 2D Superconductivity in 1H‐TaS 2 Superlattices

Noncentrosymmetric transition metal dichalcogenide (TMD) monolayers offer a fertile platform for exploring unconventional Ising superconductivity (SC) and charge density waves (CDWs). However, the vulnerability of isolated monolayers to structural disorder and environmental oxidation often degrade their electronic coherence. Herein, an alternative approach is reported for fabricating stable and intrinsic monolayers of 1H-TaS2 sandwiched between SnS blocks in a (SnS) 1.15 TaS 2 van der Waals (vdW) superlattice. The SnS block layers not only decouple individual 1H-TaS 2 sublayers to endow them with monolayer-like electronic characteristics, but also protect the 1H-TaS 2 layers from electronic degradation. The results reveal the characteristic 3 × 3 CDW order in 1H-TaS 2 sublayers associated with electronic rearrangement in the low-lying sulfur p band, which uncovers a previously undiscovered CDW mechanism rather than the conventional Fermi surface-related framework. Additionally, the (SnS) 1.15 TaS 2 superlattice exhibits a strongly enhanced Ising-like SC with a layer-independent T c of ≈3.0 K, comparable to that of the isolated monolayer 1H-TaS 2 sample, presumably attributed to their monolayer-like characteristics and retained Fermi states. These results provide new insights into the long-debated CDW order and enhanced SC of monolayer 1H-TaS 2 , establishing bulk vdW superlattices as promising platforms for investigating exotic collective quantum phases in the 2D limit.

2D superconductivity↗
DOE OSTI2024

Mechanochemically Enabled Metastable Niobium Tungsten Oxides

Metastable compounds have greatly expanded the synthesizable compositions of solid-state materials and have attracted enormous amounts of attention in recent years. Especially, mechanochemically enabled metastable materials synthesis has been very successful in realizing cation-disordered materials with highly simple crystal structures, such as rock salts. Application of the same strategy for other structural types, especially for non-close-packed structures, is peculiarly underexplored. Niobium tungsten oxides (NbWOs), a class of materials that have been under the spotlight because of their diverse structural varieties and promising electrochemical and thermoelectric properties, are ideally suited to fill such a knowledge gap. In this work, we develop a new series of metastable NbWOs and realize one with a fully cation-disordered structure. Furthermore, we find that metastable NbWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close-packed–close-packed conversion process, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. Lastly, by comparing the cation-disordered NbWO with other trending cation-disordered oxides, we raise a few key structural features for cation disorder and suggest a few possible research opportunities for this field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Electronic and structural properties of RbCe X 2 ( X 2 : O 2 , S 2 , SeS, Se 2 , TeSe, Te 2 )

We report triangular lattice delafossite compounds built from magnetic lanthanide ions are a topic of recent interest due to their frustrated magnetism and realization of quantum disordered magnetic ground states. Here we report the evolution of the structure and electronic ground states of RbCeX 2 compounds, built from a triangular lattice of Ce 3+ ions, upon varying their anion character (X 2 =O 2 , S 2 , SeS, Se 2 , TeSe, Te 2 ). This includes the discovery of a new member of this series, RbCeO 2 , that potentially realizes a quantum disordered ground state analogous to NaYbO 2 . Magnetization and susceptibility measurements reveal that all compounds manifest mean-field antiferromagnetic interactions and, with the exception of the oxide, possess signatures of magnetic correlations onset below 1 K. The crystalline electric field level scheme is explored via neutron scattering and ab initio calculations in order to model the intramultiplet splitting of the J=5/2 multiplet. In addition to the two excited doublets expected within the J=5/2 manifold, we observe one extra local mode present across the sample series. This added mode shifts downward in energy with increasing anion mass and decreasing crystal field strength, suggesting a long-lived anomalous mode endemic to anion motion about the Ce3 + sites.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Attosecond spectroscopy of size-resolved water clusters

Electron dynamics in water are of fundamental importance for a broad range of phenomena, but their real-time study faces numerous conceptual and methodological challenges. Here, in this paper, we introduce attosecond size-resolved cluster spectroscopy and build up a molecular-level understanding of the attosecond electron dynamics in water. We measure the effect that the addition of single water molecules has on the photoionization time delays of water clusters. We find a continuous increase of the delay for clusters containing up to four to five molecules and little change towards larger clusters. We show that these delays are proportional to the spatial extension of the created electron hole, which first increases with cluster size and then partially localizes through the onset of structural disorder that is characteristic of large clusters and bulk liquid water. These results indicate a previously unknown sensitivity of photoionization delays to electron-hole delocalization and indicate a direct link between electronic structure and attosecond photoionization dynamics. Our results offer new perspectives for studying electron-hole delocalization and its attosecond dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Human TRPV1 structure and inhibition by the analgesic SB-366791

Pain therapy has remained conceptually stagnant since the opioid crisis, which highlighted the dangers of treating pain with opioids. An alternative addiction-free strategy to conventional painkiller-based treatment is targeting receptors at the origin of the pain pathway, such as transient receptor potential (TRP) ion channels. Thus, a founding member of the vanilloid subfamily of TRP channels, TRPV1, represents one of the most sought-after pain therapy targets. The need for selective TRPV1 inhibitors extends beyond pain treatment, to other diseases associated with this channel, including psychiatric disorders. Here we report the cryo-electron microscopy structures of human TRPV1 in the apo state and in complex with the TRPV1-specific nanomolar-affinity analgesic antagonist SB-366791. SB-366791 binds to the vanilloid site and acts as an allosteric hTRPV1 inhibitor. SB-366791 binding site is supported by mutagenesis combined with electrophysiological recordings and can be further explored to design new drugs targeting TRPV1 in disease conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Relationship between atomic and electronic structure in Ln-bearing oxides

Metastable states of matter are of great interest as they offer the promise of novel functionality. They are often a natural consequence of exposure to nonequilibrium environments. In oxides, metastability can take the form of new polymorphs, chemical disorder, and even amorphization. While significant attention has been given to the impact those changes have on the atomic properties of the material, the corresponding changes in the electronic structure have received less attention. Here, using density functional theory, we consider how the electronic structure varies with potential metastable structures in two classes of lanthanide-bearing oxides—pyrochlores and interlanthanide sesquioxides. We find that the changes depend strongly on both the crystal structure and crystal chemistry of the compound with, for example, disordering and amorphization either increasing or decreasing the bandgap depending on the chemistry. For the 𝐴 2 ⁢𝐵 2 ⁢O 7 pyrochlores, we find different dependencies of the bandgap on the 𝐴 = 𝐿⁢𝑛 cations as the 𝐵 cation is changed, which we relate to the nature of the density of states at the conduction band minimum for different 𝐵 chemistries. Our calculations are validated by electron energy loss spectroscopy measurements for two pyrochlore compounds in which amorphization does reduce the bandgap, consistent with our calculations on these two compounds. In conclusion, our results highlight the relationship between atomic and electronic structure and how radiation can be used to modify and potentially control the electronic properties of oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Local Distortions and Metal–Semiconductor–Metal Transition in Quasi-One-Dimensional Nanowire Compounds AV 3 Q 3 O δ (A = K, Rb, Cs and Q = Se, Te)

Metal cluster compounds have garnered renewed interest in the search for novel superconductors and topological semimetals owing to structural instabilities of metal-cluster geometries and broken symmetries. Here we synthesized needle-like crystals of the V-cluster-based quasi-one-dimensional (Q1D) materials AV 3 Q 3 O δ (A = K, Rb, Cs, Q= Se, Te) which can also be viewed as being composed of parallel nanowires. We examine how changes in their average and local structure control their electronic properties. All compounds crystallize in the TIFe 3 Te 3 -type structure (P6 3 /m space group) with infinite (V 3 )Q 3 ) - double-walled columnar chains separated by A + cations. Our single-crystal and synchrotron powder diffraction studies indicate oxygen atoms partially occupy the center site of the V 6 octahedral metal cluster cages in KV 3 Te 3 O 0.33 , RbV 3 Te 3 O 0.32 , and CsV 3 Te 3 O 0.35 , whereas KV 3 Se 3 is structurally oxygen-free. Our synchrotron X-ray pair distribution function (PDF) analyses indicate that the oxygen-free V 6 cluster octahedra in KV 3 Se 3 are highly distorted perpendicular to the chain direction even at room temperature, reducing the symmetry of the average structure from hexagonal P6 3 /m to monoclinic P2 1 /m. Our theoretical calculation supports this P2 1 /m distortion and suggests the structure further distorts to P2 1 or P2 1 /c at lower temperatures. In contrast, the oxygen-centered V-cluster in KV 3 Te 3 O 0.33 exhibits a V-3-triangle-trimerization along the chain direction. This feature is discernible from the local PDF and is consistent with lattice dynamical calculations based on density functional theory. Resistivity measurements indicate that KV 3 Se 3 exhibits metallic behavior, whereas a dramatic metal-semiconductor-metal transition emerges in KV 3 Te 3 O 6.33 , RbV 3 Te 3 O 0.32 , and CsV 3 Te 3 O 0.35 because of oxygen disorder and changes in local structure captured from our electronic structure analyses of the Fermi surface. Our investigation of the AV 3 Q 3 O 6 family demonstrates the importance of understanding local changes in structure driven by electronic instabilities, which can guide the search for new quantum materials in other low-dimensional cluster-compound materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Bandgap analysis and carrier localization in cation-disordered ZnGeN 2

The bandgap of ZnGeN 2 changes with the degree of cation site disorder and is sought in light emitting diodes for emission at green to amber wavelengths. By combining the perspectives of carrier localization and defect states, we analyze the impact of different degrees of disorder on electronic properties in ZnGeN 2 , addressing a gap in current studies, which largely focus on dilute or fully disordered systems. The present study demonstrates changes in the density of states and localization of carriers in ZnGeN 2 calculated using bandgap-corrected density functional theory and hybrid calculations on partially disordered supercells generated using the Monte Carlo method. We use localization and density of states to discuss the ill-defined nature of a bandgap in a disordered material and identify site disorder and its impact on the structure as a mechanism controlling electronic properties and potential device performance. Decreasing the order parameter results in a large reduction of the bandgap. The reduction in bandgap is due, in part, to isolated, localized states that form above the valence band continuum associated with nitrogen coordinated by more zinc than germanium. The prevalence of defect states in all but the perfectly ordered structure creates challenges for incorporating disordered ZnGeN 2 into optical devices, but the localization associated with these defects provides insight into the mechanisms of electron/hole recombination in the material.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ca X ML: Chemistry‐informed machine learning explains mutual changes between protein conformations and calcium ions in calcium‐binding proteins using structural and topological features

Proteins' flexibility is a feature in communicating changes in cell signaling instigated by binding with secondary messengers, such as calcium ions, associated with the coordination of muscle contraction, neurotransmitter release, and gene expression. When binding with the disordered parts of a protein, calcium ions must balance their charge states with the shape of calcium-binding proteins and their versatile pool of partners depending on the circumstances they transmit. Accurately determining the ionic charges of those ions is essential for understanding their role in such processes. However, it is unclear whether the limited experimental data available can be effectively used to train models to accurately predict the charges of calcium-binding protein variants. Here, we developed a chemistry-informed, machine-learning algorithm that implements a game theoretic approach to explain the output of a machine-learning model without the prerequisite of an excessively large database for high-performance prediction of atomic charges. We used the ab initio electronic structure data representing calcium ions and the structures of the disordered segments of calcium-binding peptides with surrounding water molecules to train several explainable models. Network theory was used to extract the topological features of atomic interactions in the structurally complex data dictated by the coordination chemistry of a calcium ion, a potent indicator of its charge state in protein. Our design created a computational tool of Ca X ML, which provided a framework of explainable machine learning model to annotate ionic charges of calcium ions in calcium-binding proteins in response to the chemical changes in an environment. Our framework will provide new insights into protein design for engineering functionality based on the limited size of scientific data in a genome space.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Metallicity and anomalous Hall effect in epitaxially strained, atomically thin RuO 2 films

The anomalous Hall effect (AHE), a hallmark of time-reversal symmetry breaking, has been reported in rutile RuO 2 , a debated metallic altermagnetic candidate. Previously, AHE in RuO 2 was observed only in strain-relaxed thick films under extremely high magnetic fields (~50 T). Yet, in ultrathin strained films with distinctive anisotropic electronic structures, there are no reports, likely due to disorder and defects suppressing metallicity thus hindering its detection. Here, we demonstrate that ultrathin, fully strained 2 nm TiO 2 /t nm RuO 2 /TiO 2 (110) heterostructures, grown by hybrid molecular beam epitaxy, retain metallicity and exhibit a sizeable AHE at a significantly lower magnetic field (< 9 T). Density functional theory calculations reveal that epitaxial strain stabilizes a noncompensated magnetic ground state and reconfigures magnetic ordering in RuO 2 (110) thin films. These findings establish ultrathin RuO 2 as a platform for strain-engineered magnetism and underscore the transformative potential of epitaxial design in advancing spintronic technologies.

MBE↗
DOE OSTI2023

Analysis of Organic Electron Materials using Neutron Scattering (Final Report)

Neutron scattering is a powerful suite of measurement techniques that enable unique analysis of structure and dynamics of a wide variety of materials. Specifically, neutrons interact strongly with protons, which enables excellent contrast in light element organic materials that cannot be obtained with any other measurements. This series of three proposals focused on using inelastic neutron scattering (INS) to study the vibrations (dynamics) of the organic molecules involved in organic electronic devices. Our main goals were to demonstrate that INS is capable of elucidating new, useful, and unique knowledge about organic electronic samples that could be used to improve the function of devices or to solve outstanding problems that could not be solved using other measurement techniques. Since all of the goal involved using INS or other neutron techniques to do something “new” a large part of the effort was focused on complex data interpretation and development of modeling workflows that could be used by other members of the organic electronics community to study their materials. To facilitate the goal of making INS measurements more accessible to a broader community and for a wider range of materials, we optimized and engineered the computational workflows to be well documented, publicly available, and user friendly. The individual titles of the three sequential DOE-BES awards are: (1) Engineering doping profiles in organic semiconducting materials, (2) Measurement and modeling of molecular dopant structure and dynamics, and (3) Quantification of Dynamic Disorder in Electronic and Excitonic Organic Materials. For readability, this report is organized to highlight the progress of the research thematically. Many of the ideas started in one grant period and then spilled over into later awards and collaborative research.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural disorder-driven topological phase transition in noncentrosymmetric BiTeI

In this work, we investigate using local structural disorder to induce a topologically nontrivial phase in a solid state system. Using first-principles calculations, we introduce structural disorder in the trivial insulator BiTeI and observe the emergence of a topological insulating phase. By modifying the bonding environments, the crystal-field splitting is enhanced, with spin-orbit interactions producing a band inversion in the bulk electronic structure. Analysis of the Wannier charge centers and the surface electronic structure reveals a strong topological insulator with Dirac surface states. Finally, we propose a prescription for inducing topological states from disorder in crystalline materials. Understanding how local environments produce topological phases is a key step for predicting disordered and amorphous topological materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗