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DOE OSTI2020

Materials Data on KTaWO7 by Materials Project

(KTaWO6)2O2 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional and consists of four water molecules and one KTaWO6 framework. In the KTaWO6 framework, K is bonded in a hexagonal planar geometry to six O atoms. There are two shorter (2.72 Å) and four longer (2.76 Å) K–O bond lengths. Ta is bonded to six O atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra and corners with four equivalent WO6 octahedra. The corner-sharing octahedra tilt angles range from 37–38°. There is two shorter (1.99 Å) and four longer (2.00 Å) Ta–O bond length. W is bonded to six O atoms to form WO6 octahedra that share corners with two equivalent WO6 octahedra and corners with four equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 36–37°. There is four shorter (1.94 Å) and two longer (1.96 Å) W–O bond length. There are three inequivalent O sites. In the first O site, O is bonded in a 4-coordinate geometry to two equivalent K and two equivalent Ta atoms. In the second O site, O is bonded in a bent 150 degrees geometry to two equivalent W atoms. In the third O site, O is bonded in a 3-coordinate geometry to one K, one Ta, and one W atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaNbAl6 by Materials Project

TaNbAl6 is beta Cu3Ti-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ta is bonded to twelve Al atoms to form TaAl12 cuboctahedra that share corners with four equivalent TaAl12 cuboctahedra, corners with eight equivalent AlNb4Al8 cuboctahedra, edges with eight equivalent NbAl12 cuboctahedra, edges with sixteen equivalent AlTa2Nb2Al8 cuboctahedra, faces with four equivalent TaAl12 cuboctahedra, and faces with fourteen AlNb4Al8 cuboctahedra. There are four shorter (2.73 Å) and eight longer (2.88 Å) Ta–Al bond lengths. Nb is bonded to twelve Al atoms to form NbAl12 cuboctahedra that share corners with four equivalent NbAl12 cuboctahedra, corners with eight equivalent AlTa4Al8 cuboctahedra, edges with eight equivalent TaAl12 cuboctahedra, edges with sixteen equivalent AlTa2Nb2Al8 cuboctahedra, faces with four equivalent NbAl12 cuboctahedra, and faces with fourteen AlNb4Al8 cuboctahedra. There are four shorter (2.73 Å) and eight longer (2.89 Å) Nb–Al bond lengths. There are three inequivalent Al sites. In the first Al site, Al is bonded to four equivalent Nb and eight equivalent Al atoms to form AlNb4Al8 cuboctahedra that share corners with four equivalent AlNb4Al8 cuboctahedra, corners with eight equivalent TaAl12 cuboctahedra, edges with twenty-four AlTa4Al8 cuboctahedra, faces with two equivalent TaAl12 cuboctahedra, faces with four equivalent NbAl12 cuboctahedra, and faces with twelve AlNb4Al8 cuboctahedra. All Al–Al bond lengths are 2.89 Å. In the second Al site, Al is bonded to four equivalent Ta and eight equivalent Al atoms to form distorted AlTa4Al8 cuboctahedra that share corners with four equivalent AlTa4Al8 cuboctahedra, corners with eight equivalent NbAl12 cuboctahedra, edges with twenty-four AlNb4Al8 cuboctahedra, faces with two equivalent NbAl12 cuboctahedra, faces with four equivalent TaAl12 cuboctahedra, and faces with twelve AlTa4Al8 cuboctahedra. All Al–Al bond lengths are 2.88 Å. In the third Al site, Al is bonded to two equivalent Ta, two equivalent Nb, and eight Al atoms to form AlTa2Nb2Al8 cuboctahedra that share corners with twelve equivalent AlTa2Nb2Al8 cuboctahedra, edges with four equivalent TaAl12 cuboctahedra, edges with four equivalent NbAl12 cuboctahedra, edges with sixteen AlNb4Al8 cuboctahedra, faces with two equivalent TaAl12 cuboctahedra, faces with two equivalent NbAl12 cuboctahedra, and faces with fourteen AlNb4Al8 cuboctahedra. All Al–Al bond lengths are 2.73 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr3LaTa2(CoO6)2 by Materials Project

Sr3LaTa2(CoO6)2 is (Cubic) Perovskite-derived structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are six inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent LaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, a faceface with one LaO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.75–2.92 Å. In the second Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent LaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, a faceface with one LaO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.81–2.95 Å. In the third Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent LaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, a faceface with one LaO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.71–3.06 Å. In the fourth Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with two SrO12 cuboctahedra, faces with four equivalent LaO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.77–2.89 Å. In the fifth Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent LaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, a faceface with one LaO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.74–3.03 Å. In the sixth Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with two SrO12 cuboctahedra, faces with four equivalent LaO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.79–2.92 Å. There are two inequivalent La3+ sites. In the first La3+ site, La3+ is bonded to twelve O2- atoms to form LaO12 cuboctahedra that share corners with four equivalent LaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of La–O bond distances ranging from 2.71–2.98 Å. In the second La3+ site, La3+ is bonded to twelve O2- atoms to form distorted LaO12 cuboctahedra that share corners with four equivalent LaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four TaO6 octahedra, and faces with four CoO6 octahedra. There are a spread of La–O bond distances ranging from 2.67–3.04 Å. There are four inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share a cornercorner with one TaO6 octahedra, corners with five CoO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 3–9°. There are a spread of Ta–O bond distances ranging from 1.91–2.05 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two TaO6 octahedra, corners with four equivalent CoO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 3–10°. There are a spread of Ta–O bond distances ranging from 1.97–1.99 Å. In the third Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share a cornercorner with one TaO6 octahedra, corners with five CoO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 3–6°. There are a spread of Ta–O bond distances ranging from 1.93–2.07 Å. In the fourth Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with six CoO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 1–8°. There are a spread of Ta–O bond distances ranging from 1.97–2.07 Å. There are four inequivalent Co+2.50+ sites. In the first Co+2.50+ site, Co+2.50+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with six TaO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 1–8°. There are a spread of Co–O bond distances ranging from 2.01–2.07 Å. In the second Co+2.50+ site, Co+2.50+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one CoO6 octahedra, corners with five TaO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 3–9°. There are a spread of Co–O bond distances ranging from 1.91–2.07 Å. In the third Co+2.50+ site, Co+2.50+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with two CoO6 octahedra, corners with four equivalent TaO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–10°. There are a spread of Co–O bond distances ranging from 1.81–2.08 Å. In the fourth Co+2.50+ site, Co+2.50+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one CoO6 octahedra, corners with five TaO6 octahedra, faces with two equivalent LaO12 cuboctahedra, and faces with six SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–6°. There are three shorter (2.06 Å) and three longer (2.07 Å) Co–O bond lengths. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to four Sr2+ and two Co+2.50+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the fifth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Sr2+, two equivalent La3+, one Ta5+, and one Co+2.50+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the seventh O2- site, O2- is bonded in a distorted linear geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the eighth O2- site, O2- is bonded in a distorted linear geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the ninth O2- site, O2- is bonded in a distorted linear geometry to four Sr2+, one Ta5+, and one Co+2.50+ atom. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the eleventh O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the twelfth O2- site, O2- is bonded in a distorted linear geometry to four Sr2+, one Ta5+, and one Co+2.50+ atom. In the thirteenth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the fourteenth O2- site, O2- is bonded in a distorted linear geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the fifteenth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the sixteenth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Sr2+, two equivalent La3+, and two Co+2.50+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Sr2+, two equivalent La3+, and two Ta5+ atoms. In the eighteenth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the nineteenth O2- site, O2- is bonded in a distorted linear geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the twentieth O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the twenty-first O2- site, O2- is bonded in a distorted linear geometry to four Sr2+ and two Ta5+ atoms. In the twenty-second O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the twenty-third O2- site, O2- is bonded in a 2-coordinate geometry to three Sr2+, one La3+, one Ta5+, and one Co+2.50+ atom. In the twenty-fourth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Sr2+, two equivalent La3+, one Ta5+, and one Co+2.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li(TaS2)2 by Materials Project

Li(TaS2)2 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Li(TaS2)2 sheet oriented in the (0, 0, 1) direction. Li1+ is bonded to six equivalent S2- atoms to form LiS6 octahedra that share corners with twelve equivalent TaS6 pentagonal pyramids, edges with six equivalent LiS6 octahedra, and faces with two equivalent TaS6 pentagonal pyramids. All Li–S bond lengths are 2.56 Å. Ta+3.50+ is bonded to six S2- atoms to form distorted TaS6 pentagonal pyramids that share corners with six equivalent LiS6 octahedra, edges with six equivalent TaS6 pentagonal pyramids, and a faceface with one LiS6 octahedra. The corner-sharing octahedral tilt angles are 45°. There are three shorter (2.47 Å) and three longer (2.51 Å) Ta–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Li1+ and three equivalent Ta+3.50+ atoms to form a mixture of distorted corner and edge-sharing SLi3Ta3 pentagonal pyramids. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Ta+3.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta5CrNiS10 by Materials Project

Ta2CrS4Ta2NiS4TaS2 crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of two Ta2CrS4 sheets oriented in the (0, 0, 1) direction; two Ta2NiS4 sheets oriented in the (0, 0, 1) direction; and two TaS2 sheets oriented in the (0, 0, 1) direction. In each Ta2CrS4 sheet, Ta3+ is bonded to six S2- atoms to form distorted TaS6 pentagonal pyramids that share corners with six equivalent CrS6 octahedra, edges with six equivalent TaS6 pentagonal pyramids, and a faceface with one CrS6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are three shorter (2.48 Å) and three longer (2.52 Å) Ta–S bond lengths. Cr3+ is bonded to six equivalent S2- atoms to form CrS6 octahedra that share corners with twelve equivalent TaS6 pentagonal pyramids, edges with six equivalent CrS6 octahedra, and faces with two equivalent TaS6 pentagonal pyramids. All Cr–S bond lengths are 2.43 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Ta3+ and three equivalent Cr3+ atoms to form a mixture of distorted corner and edge-sharing STa3Cr3 pentagonal pyramids. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Ta3+ atoms. In each Ta2NiS4 sheet, there are two inequivalent Ta3+ sites. In the first Ta3+ site, Ta3+ is bonded to six S2- atoms to form distorted TaS6 pentagonal pyramids that share corners with six equivalent NiS6 octahedra, edges with six equivalent TaS6 pentagonal pyramids, and a faceface with one NiS6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Ta–S bond lengths are 2.48 Å. In the second Ta3+ site, Ta3+ is bonded to six S2- atoms to form distorted TaS6 pentagonal pyramids that share corners with six equivalent NiS6 octahedra, edges with six equivalent TaS6 pentagonal pyramids, and a faceface with one NiS6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Ta–S bond lengths are 2.48 Å. Ni2+ is bonded to six S2- atoms to form NiS6 octahedra that share corners with twelve TaS6 pentagonal pyramids, edges with six equivalent NiS6 octahedra, and faces with two TaS6 pentagonal pyramids. All Ni–S bond lengths are 2.38 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Ta3+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Ta3+ atoms. In the third S2- site, S2- is bonded to three equivalent Ta3+ and three equivalent Ni2+ atoms to form a mixture of distorted corner and edge-sharing STa3Ni3 pentagonal pyramids. In the fourth S2- site, S2- is bonded to three equivalent Ta3+ and three equivalent Ni2+ atoms to form a mixture of distorted corner and edge-sharing STa3Ni3 pentagonal pyramids. In each TaS2 sheet, Ta3+ is bonded to six equivalent S2- atoms to form distorted edge-sharing TaS6 pentagonal pyramids. All Ta–S bond lengths are 2.48 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Ta3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta2InS4 by Materials Project

Ta2InS4 crystallizes in the orthorhombic Imm2 space group. The structure is three-dimensional. Ta+3.50+ is bonded to six S2- atoms to form distorted edge-sharing TaS6 pentagonal pyramids. There are a spread of Ta–S bond distances ranging from 2.47–2.50 Å. In1+ is bonded in a 6-coordinate geometry to six S2- atoms. There are two shorter (3.09 Å) and four longer (3.15 Å) In–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to three equivalent Ta+3.50+ and two equivalent In1+ atoms. In the second S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three equivalent Ta+3.50+ and one In1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Ultrathin Magnesium-Based Coating as an Efficient Oxygen Barrier for Superconducting Circuit Materials

Scaling up superconducting quantum circuits based on transmon qubits necessitates substantial enhancements in qubit coherence time. Over recent years, tantalum (Ta) has emerged as a promising candidate for transmon qubits, surpassing conventional counterparts in terms of coherence time. However, amorphous surface Ta oxide layer may introduce dielectric loss, ultimately placing a limit on the coherence time. In this study, a novel approach for suppressing the formation of tantalum oxide using an ultrathin magnesium (Mg) capping layer is presented. Synchrotron-based X-ray photoelectron spectroscopy studies demonstrate that oxide is confined to an extremely thin region directly beneath the Mg/Ta interface. Additionally, it is demonstrated that the superconducting properties of thin Ta films are improved following the Mg capping, exhibiting sharper and higher-temperature transitions to superconductive and magnetically ordered states. Moreover, an atomic-scale mechanistic understanding of the role of the capping layer in protecting Ta from oxidation is established based on computational modeling. Further, this work provides valuable insights into the formation mechanism and functionality of surface tantalum oxide, as well as a new materials design principle with the potential to reduce dielectric loss in superconducting quantum materials. Ultimately, the findings pave the way for the realization of large-scale, high-performance quantum computing systems.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Revealing the Origin and Nature of the Buried Metal‐Substrate Interface Layer in Ta/Sapphire Superconducting Films

Abstract Despite constituting a smaller fraction of the qubit's electromagnetic mode, surfaces and interfaces can exert significant influence as sources of high‐loss tangents, which brings forward the need to reveal properties of these extended defects and identify routes to their control. Here, we examine the structure and composition of the metal‐substrate interfacial layer that exists in Ta/sapphire‐based superconducting films. Synchrotron‐based X‐ray reflectivity measurements of Ta films, commonly used in these qubits, reveal an unexplored interface layer at the metal‐substrate interface. Scanning transmission electron microscopy and core‐level electron energy loss spectroscopy identified an intermixing layer (≈0.65 ± 0.05 nm) at the metal‐substrate interface containing Al, O, and Ta atoms. Density functional theory modeling reveals that the structure and properties of the Ta/sapphire heterojunctions are determined by the oxygen content on the sapphire surface prior to Ta deposition for two atomic terminations of sapphire. Using a multimodal approach, we gained deeper insights into the interface layer between the metal and substrate, which suggests that the orientation of deposited Ta films depend on the surface termination of sapphire. The observed elemental intermixing at the metal‐substrate interface influences the thermodynamic stability and electronic behavior of the film, which may also affect qubit performance.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fe‐Triazolate Metal–Organic Frameworks as Water Oxidation Catalysts with Dual Photoanode Functionality

Artificial photosynthesis is an emerging technology that achieves renewable fuels, such as hydrogen, from sunlight. Its realization depends on finding highly active and stable catalysts of water splitting and photoactive materials for light absorption. To be scalable, these should contain only abundant elements. Here, for the first time, Fe-triazolate (Fe(ta) 2 ) and its metal substituted derivatives (Fe-Metal(ta) 2 ) Metal-organic frameworks (MOFs) are characterized as new dual-function materials for photo-absorption and water oxidation catalysis in acidic media. The materials were studied by a range of structural, spectroscopic, and computational density functional theory (DFT) techniques. Fe(ta) 2 and Fe-Mn(ta) 2 were found to be highly active and stable in chemical and photochemical water oxidation, and in addition function as photoanodes, with photo-electrocatalytic currents (∼2.00 x 10 −3 Acm −2 at + 1.4 V vs. Ag/AgCl) at pH = 1. The possibility of a unique catalytic mechanism where O─O bond formation is possible from the coupling of two adjacent Fe IV = O fragments was demonstrated by DFT analysis. Thus, Fe-triazolate MOF has been established as a new, stable, scalable, versatile, and efficient platform for sustainable energy conversion in the realm of artificial photosynthesis.

Artificial photosynthesis↗
DOE OSTI2021

Efficient Screening of Bi–Metallic Electrocatalysts for Glycerol Valorization

Glycerol is a byproduct of biodiesel production and, as such, it is of limited economic value. By means of electrooxidation, glycerol can be used as a feedstock for scalable hydrogen production, in addition to conversion to value-added products. The development of novel and efficient catalytic electrode materials for the anodic side of the reaction is a key towards a hydrogen-based energy economy. In the present study, a computational screening protocol combining DFT, scaling relations, and microkinetic modeling allows for a rational selection of novel catalysts that can deliver efficient glycerol electrooxidation, low cost of production, and environmental sustainability. Activity and chemical selectivity towards hydrogen production on pure metal catalysts is discussed in terms of volcano-shaped plots. We find that the selectivity in the glycerol oxidation reaction is influenced by a different energy landscape when in the presence of water and best classified by a comparison of O—H and C—H bond-breaking barriers. In addition, we screened 3570 bi-metallic catalysts in the AB (L1 0 ) and A 3 B (L1 2 ) ordered structures for activity, stability, price, and toxicity. By filtering based on the criteria for toxicity, resistance to oxidation, miscibility, and price, we have identified 5 L1 0 structured catalysts (AgPd, AuPd, PtSb, CuPt, and AgPt) and 20 L1 2 catalysts (Ga 3 Ta, In 3 Ta, Ir 3 W, Ir 3 Mo, Cu 3 Pt, Ir 3 Ta, Ir 3 Re, Pd 3 Bi, Pd 3 Cu, Pd 3 W, Pd 3 Co, Pd 3 Sn, Pd 3 Mo, Pd 3 Ag, Pd 3 Ga, Pd 3 Ta, Au 3 Ru, Pd 3 In, Au 3 Ir, and Pd 3 Au) that are all predicted to show high activity. We also identify an additional 37 L1 0 and 92 L1 2 structured electrocatalysts with an anticipated medium-high activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Solidification cracking of refractory alloys: a computational and machine learning study to investigate composition-dependence for improved weldability and additive manufacturability

Large-batch numerical, CALculation of PHAse Diagrams (CALPHAD)-based solidification cracking calculations are performed and then analyzed with machine learning methods to generate models that relate chemistry of refractory alloys to cracking susceptibility. Kou’s solidification cracking index is used to study the refractory alloys including O, N, C binary mixtures with Mo, Ta, Nb, and W, the molybdenum-based TZM, Niobium-based C103, and Tantalum-based T111 and Ta-10 W, as well as hypothetical refractory ternary alloys. Findings strongly validate Kou’s Crack Susceptibility Index (CSI) against Varestraint test data for Nb- and Ta-based alloys, establishing CSI thresholds where refractory alloys with CSI < 15,000 K are likely weldable, CSI > 15,000 K are prone to cracking, and CSI > 25,000 K are likely unweldable (or unprintable). Furthermore, interstitial elements C, N, and O significantly increase crack susceptibility, with some existing material specifications coinciding with peak cracking susceptibility concentrations. Finally, machine learning-derived elemental potency factors enable rapid prediction of CSI from alloy chemistry for C103, TZM, Ta-10 W, and T-111 alloys. These results provide practical guidance for feedstock selection, powder reuse limits, and alloy specification amendments for welding and additive manufacturing applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Single-Atom Doping at the Molecule–Metal Interface: How Rh Affects Surface Explosion Kinetics

Controlling chemical reactions at interfaces is central to many fields, including atmospheric, environmental, and biological chemistry as well as catalysis and corrosion. We performed a fundamental study of how catalytically active Rh atoms placed at and above a molecule-metal interface influence the surface reaction kinetics of tartaric acid (TA) decomposition. Specifically, TA decomposition on Cu(100) exhibits autocatalytic decomposition kinetics involving a slow initiation step followed by fast decomposition of the molecular layer. These so-called “surface explosions” are extremely sensitive to initial conditions, making it fundamentally interesting to study how the placement of reactive atoms affects the reaction rate. Temperature-programmed reaction (TPR) experiments reveal that Rh atoms embedded in the Cu(100) surface beneath TA (TA/Rh/Cu) or atop the TA layer (Rh/TA/Cu) reduce the decomposition temperature and modify the reaction rate constants. Isothermal TPR analysis reveals that Rh enhances both the initiation rate constant, k i , and the explosion rate constant, k e , facilitating explosive decomposition at lower temperatures. This result provides evidence that both the initiation and explosion steps occur at the metal-molecule interface and are accelerated by the presence of Rh at this interface. This study illustrates how small amounts of reactive elements may be used to control nonlinear kinetic processes at interfaces.

desorption↗
DOE OSTI2020

Tilted fluctuation electron microscopy

Fluctuation electron microscopy (FEM) is a scanning nanodiffraction-based method that offers a unique approach to characterizing nanometer-scale medium-range order (MRO) in disordered materials. In addition to determining the degree of MRO, careful analysis of scanning nanodiffraction data can also be used to determine strain in thin film amorphous samples. We applied FEM to characterize the strain and MRO of magnetron sputtered amorphous tantalum (a-Ta) thin films over a range of tilt angles from 0° to 45° in order to measure any deviations between the in-plane and out-of-plane strain and MRO. We validate our approach using electron diffraction simulations of FEM experiments for a-Ta. We measure anisotropic strain in the simulated a-Ta diffraction patterns and find that the experimental a-Ta is isotropically strained within the accuracy of our method. Our approach provides a workflow for acquiring tilted scanning nanodiffraction data, determining the relative strain and ordering as a function of in- A nd out-of-plane directions, and removing any artifacts induced in FEM data due to strain. We also describe some limitations of the tilted FEM method when applied to thin films with very low strains.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effects of irradiation damage on the hardness and elastic properties of quaternary and high entropy transition metal diborides

Multi-principal component transition metal (TM) diborides represent a class of high-entropy ceramics (HECs) that have received considerable interest in recent years owing to their promising properties for extreme environment applications that include thermal/ environmental barriers, hypersonic vehicles, turbine engines, and next-generation nuclear reactors. While the addition of chemical disorder through the random distribution of TM elements on the cation sublattice has offered opportunities to tailor elastic stiffness and hardness, the effects of irradiation-induced structural damage on the physical properties of these complex materials have remained largely unexplored. To this end, changes in the hardness and elastic moduli of a high-entropy TM diboride (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2 )B 2 and three of its quaternary subsets following irradiation with 10 MeV gold (Au) ions to fluences of up to 6 × 10 15 Au cm -2 are investigated at the micrometer and sub-micrometer length-scales via the dispersion of laser-generated surface acoustic waves (SAW) and nanoindentation, respectively. The nanoindentation measurements show that the TM diborides exhibit an initial increase in hardness following irradiation with energetic Au ions, with a subsequent decrease in hardness following further irradiation. One quaternary composition, (Hf 1/3 Ta 1/3 Ti 1/3 )B 2 , exhibits a notable exception to the trend and continues to exhibit an increase in hardness with ion irradiation fluence. Although differences in the absolute values of the effective elastic moduli obtained from the measured SAW dispersion and nanoindentation are observed (and attributed to microstructural variations at the measurement length-scale), both techniques yield similar trends in the form of an initial reduction and subsequent saturation in the elastic modulus with increasing ion irradiation fluence. The quaternary TM diboride (Hf 1/3 Ta 1/3 Ti 1/3 )B 2 again exhibits a departure from this trend. The high-entropy TM diboride (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2 )B 2 exhibits the greatest recovery in hardness and modulus when irradiated to high ion fluences following initial changes at low fluence, indicating superior resistance to radiation-induced damage over its quaternary counterparts. Opportunities for designing HECs with superior hardness and modulus for enhanced radiation resistance (compared to their single constituent counterparts) by tailoring chemical disorder and bond character in the lattice are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Heat metrics and thresholds reshape population exposure and inequality signals

Extreme heat is intensifying worldwide, yet estimates of heat hazard and exposure inequality depend on both the heat metric and how extreme days are defined. Using summer 2022 across the Mediterranean, we quantify population heat exposure with four metrics—land surface temperature (LST), air temperature (Ta), heat index (HI), and wet-bulb globe temperature (WBGT)—under absolute (fixed-value) and relative (anomaly-based) thresholds. Under absolute thresholds, total heat exposure differs by more than two orders of magnitude across metrics (31.3 billion person-days for Ta vs 0.3 billion for HI). Geographic hotspots also diverge: WBGT concentrates in humid coastal North Africa (e.g. the Nile Delta), whereas Ta and LST are more widespread. Under relative thresholds, exposure totals converge and cross-metric hotspot agreement increases (e.g. Ta–WBGT top-tercile overlap increases from 10.7% to 29.0%), shifting hotspots toward densely populated southern Europe. Crucially, the exposure–deprivation relationship also reverses across threshold frameworks: absolute thresholds concentrate exposure in more deprived North Africa and the Middle East, whereas relative thresholds shift the burden toward less-deprived European cities. This sensitivity is decision-relevant: city rankings based on WBGT exposure duration are almost completely reordered when switching threshold frameworks. Threshold choice therefore systematically reshapes hotspot patterns and inequality signals. Reporting both absolute and relative exposures can reveal hidden hotspots and support more targeted heat-risk monitoring and intervention planning.

Mediterranean↗
DOE OSTI2025

Structural stability, elemental ordering, and transport properties of layered ScTaN 2

Ternary transition metal (TM) nitrides have gained significant attention in thin film research due to their promising properties for a broad range of applications. Particularly, some of the ternary TM nitrides have been predicted to adopt layered structures that make them interesting for thermoelectric conversion and quantum materials applications. Unfortunately, synthesis of TM ternary nitride films by physical vapor deposition often favors disordered 3D structures rather than the predicted 2D-like layered structure. In this study, we investigate the structural interplay in the Sc-Ta-N ternary system using a combinatorial approach. Combinatorial libraries S⁢c 𝑥 ⁢T⁢a 1−𝑥 ⁢N are synthesized following a two-step method: First, deposit film precursors by cosputtering and then process the resulting 3D-structured samples with rapid thermal annealing. Synchrotron grazing-incidence wide-angle x-ray scattering on films annealed at 1200 ⁢°⁢C for 20 min leads to the nucleation of ScTaN 2 layered structure (𝑃⁢6 3 /𝑚⁢𝑚⁢𝑐) near stoichiometry. We find that the layered structure can accommodate large off-stoichiometry in the Ta-rich region (𝑥 < 0.5), facilitated by the alloying with quasi-isostructural Ta 5 ⁢N 6 compound that exists on a composition tie line at 𝑥 = 0. While focusing on ScTaN 2 , we estimate the long-range order parameter in near-stoichiometric films to be 0.86, corresponding to a fraction of Sc/Ta antisites of 7%. Transport measurements on ScTaN 2 reveal a nearly temperature-independent high carrier density (10 21 c⁢m −3 ), suggesting a heavily doped semiconductor or semimetallic character, consistent with a small positive Seebeck coefficient of +19 µV/K. The carrier mobility at 2 K is relatively small (9.5c⁢m 2 V −1 s −1 ) and the residual-resistivity ratio is minor, suggesting that electrical conduction is dominated by defects or disorder. Measured magnetoresistance suggests possible weak antilocalization at 2 K. This paper highlights the interplay between ScTaN 2 and Ta 5 ⁢N 6 crystal structures in stabilizing layered materials, emphasizes the importance of cation order/disorder for potential tunable alloys, and suggests that ScTaN 2 is a promising platform for exploring electronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Variation of sign and magnitude of the Dzyaloshinskii-Moriya interaction of a ferromagnet with an oxide interface

We demonstrate that both the magnitude and sign of the Dzyaloshinskii-Moriya interaction can be tuned by modifying the type and thickness of an oxide layer adjacent to a ferromagnet. In this work, we focus on Ti/Cu/Co 90 Fe 10 /Ta($d_{\text{Ta}}$)/Oxide/Ta structures, where the Ta interlayer thickness $d_{\text{Ta}}$ ranged from 0 nm to 3 nm, followed by an exposure to oxygen and “Oxide” can mean CoFeO x and/or TaO x . We used Brillouin light scattering spectroscopy to directly determine the volume-averaged Dzyaloshinskii-Moriya interaction from the nonreciprocity of the spin-wave frequency. The magnitude of the interfacial Dzyaloshinskii-Moriya interaction, $D_{\text{DMI}}$, ranges from – 0.17 to +0.09(±0.02) mJ/m 2 , clearly showing a change in both sign and magnitude, with an increase of Ta interlayer thickness. The modification of the oxide interface allows us to systematically change the hybridization of the 3$\textit{d}$–CoFe orbitals from 3$\textit{d}$–5$\textit{d}$ to 3$\textit{d}$–2$\textit{p}$ and analyze the influence on the Dzyaloshinskii-Moriya interaction. Importantly, we can vary the Dzyaloshinskii-Moriya interaction while maintaining a relatively small value of the damping parameter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗