Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Ti”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Suppressed electric quadrupole collectivity in 49 Ti

Single-step Coulomb excitation of 46,48,49,50 Ti is presented. A complete set of E2 matrix elements for the quintuplet of states in 49 Ti, centred on the core excitation, was measured for the first time. A total of nine E2 matrix elements are reported, four of which were previously unknown. $^{49}_{22}$Ti 27 shows a 20% quenching in electric quadrupole transition strength as compared to its semi-magic $^{50}_{22}$Ti 28 neighbour. This 20% quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connection to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the 49 Ti- 50 Ti pair (i.e., approximate single-j 0 7/2 valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Intricate Magnetic Landscape in Antiferromagnetic Kagome Metal TbTi 3 Bi 4 and Interplay with Ln 2– x Ti 6+ x Bi 9 (Ln: Tb···Lu) Shurikagome Metals

Here we present the discovery and characterization of the kagome metal TbTi 3 Bi 4 in tandem with a new series of compounds, the Ln 2–x Ti 6+x Bi 9 (Ln: Tb–Lu) shurikagome metals. We previously reported on the growth of the LnTi 3 Bi 4 (Ln: La–Gd 3+ , Eu 2+ , Yb 2+ ) family, a chemically diverse and exfoliable series of kagome metals with complex and highly anisotropic magnetism. However, unlike the La–Gd analogs, TbTi 3 Bi 4 cannot be synthesized by our previous methodology due to phase competition with crystals of Ln 2–x Ti 6+x Bi 9 (x ~ 1.7–1.2). Here we discuss the phase competition between the LnTi 3 Bi 4 and Ln 2–x Ti 6+x Bi 9 families, helping to frame the difficulty in synthesizing LnTi 3 Bi 4 compounds with small Ln species and providing a strategy to circumvent the formation of Ln 2–x Ti 6+x Bi 9 . Detailed characterization of the magnetic and electronic transport properties on single crystals of TbTi 3 Bi 4 reveals a highly complex landscape of magnetic phases arising from an antiferromagnetic ground state. A series of metamagnetic transitions creates at least 5 unique magnetic phase pockets, including a 1/3 and 2/3 magnetization plateau. Further, the system exhibits an intimate connection between the magnetism and magnetotransport, exhibiting sharp switching from positive (+40%) to negative magnetoresistance (–50%). Like the LnTi 3 Bi 4 kagome metals, the Ln 2–x Ti 6+x Bi 9 family exhibits quasi-2D networks of titanium and chains of rare earth. Finally, we present the structures and some basic magnetic properties of the Ln 2–x Ti 6+x Bi 9 family alongside our characterization of the newly discovered TbTi 3 Bi 4 .

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

Plasmonic Hot-Carrier Generation and Catalysis in Ti 3 C 2 O 2 from Real-Time TDDFT Simulations

Photoinduced hot electrons are central to plasmon-driven catalysis. Atomically thin Ti 3 C 2 O 2 , with high carrier density and broad optical absorption, offers a promising platform for plasmon-driven reactions. However, comprehensive investigations of its plasmon resonance, hot-carrier generation, and plasmonic catalytic performance remain limited. In this work, real-time time-dependent density functional theory (rt-TDDFT) was employed to study Ti 3 C 2 O 2 ’s plasmon excitation and hot-carrier generation from nonradiative plasmon damping. The temporal evolution of the dipole moment reveals plasmon resonance in Ti 3 C 2 O 2 , followed by strong plasmon damping that redistributes the stored energy to generate hot carriers. Ti 3 C 2 O 2 with low oxygen vacancy concentration (O v -Ti 3 C 2 O 2 ) exhibits plasmonic behavior resembling the pristine surface, and the plasmon-generated hot electrons can markedly reduce the dissociation barrier of CO 2 at the oxygen vacancy. These findings provide fundamental insights into the plasmonic properties of Ti 3 C 2 O 2 and how they drive its catalytic performance in surface reactions, which is valuable for advancing plasmon-driven catalysis.

CO2 reduction↗
DOE OSTI2020

Porous Ti-MOF-74 Framework as a Strong-Binding Nitric Oxide Scavenger

Combining synthesis, infrared spectroscopy, and ab initio modeling we show that the titanium-based porous framework Ti-MOF-74 has potential as an environmental nitric oxide (NO) scavenger, exhibiting an extraordinarily strong binding affinity and selectivity over other flue-gas components. The robustness upon exposure to water vapor and high flue-gas stack temperatures suggests that this material can perform well in an industrial environment. In-depth analysis of the Ti-NO bond indicates that the NO forms a strong covalent bond with the Ti. The process of this NO bond formation involves a reaction with the OH- capping groups of the Ti to form NO x groups, after which the excess NO binds to the open Ti metal sites. Ti-MOF-74 thus becomes, to the best of our knowledge, the first known porous framework that binds NO significantly stronger than water, providing novel avenues for environmental and physiological scavenging applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Facilitating Hydrogen Dissociation over Dilute Nanoporous Ti–Cu Catalysts

The dissociation of H 2 is an essential elementary step in many industrial chemical transformations, typically requiring precious metals. Here, we report a hierarchical nanoporous Cu catalyst doped with small amounts of Ti (npTiCu) that increases the rate of H 2 –D 2 exchange by approximately one order of magnitude compared to the undoped nanoporous Cu (npCu) catalyst. The promotional effect of Ti was measured via steady-state H 2 –D 2 exchange reaction experiments under atmospheric pressure flow conditions in the temperature range of 300–573 K. Pretreatment with flowing H 2 is required for stable catalytic performance, and two temperatures, 523 and 673 K, were investigated. The experimentally determined H 2 –D 2 exchange rate is 5–7 times greater for npTiCu vs the undoped Cu material under optimized pretreatment and reaction temperatures. The H 2 pretreatment leads to full reduction of Cu oxide and partial reduction of surface Ti oxide species present in the as-prepared catalyst as demonstrated using in situ ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The apparent activation energies and pre-exponential factors measured for H 2 –D 2 exchange are substantially different for Ti-doped vs undoped npCu catalysts. Density functional theory calculations suggest that isolated, metallic Ti atoms on the surface of the Cu host can act as the active surface sites for hydrogen recombination. Furthermore, the increase in the rate of exchange above that of pure Cu is caused primarily by a shift in the rate-determining step from dissociative adsorption on Cu to H/D atom recombination on Ti-doped Cu, with the corresponding decrease in activation entropy that it produces.

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

Proton, Electron, and Hydrogen-Atom Transfer Thermodynamics of the Metal–Organic Framework, Ti-MIL-125, Are Intrinsically Correlated to the Structural Disorder

Interfacial charge transfer reactions involving protons and/or electrons are fundamental to heterogeneous catalysis and many other reactions relevant to energy, chemical, and biological sectors. Metal–organic frameworks (MOFs) with redox-active metal-oxo nodes have emerged as candidate materials to examine these reactions with near-atomic-level precision, given their crystalline nature. Here, we employed a colloidally stable, Ti-based MOF, Ti-MIL-125, with different crystal sizes to examine catalytically relevant charge transfer thermodynamics. The Ti 8 (μ 2 -O) 8 (μ 2 -OH) 4 nodes structurally mimic TiO 2 , which has shown some PCET reactivity toward reactions of H 2 , O 2 , and others. In this report, we have demonstrated that a change in crystal size induces different amounts of structural disorder to the Ti-oxo node, further changing the thermodynamics of proton/electron/hydrogen-atom transfer reactions. Using electrochemical open-circuit potential (E OCP ) measurements, we have determined that all crystallites undergo a 1H + /1e – redox reaction, which, given the stoichiometry, can be considered as a net H atom transfer (HAT) reaction. The thermodynamics of this HAT reaction, the Ti 3+ O–H bond dissociation free energy (BDFE), was dependent on the crystal size of the MOF, as the decrease in crystal size induced more structural disorder. Our computational calculations have indicated that this difference in BDFE is due to a local change in the geometry of Ti cations, rather than the commonly invoked defects, such as the “missing-linker” defect sites. Individual proton/electron transfer (PT/ET) thermodynamics were also highly dependent on the crystal sizes. These were probed using pK a or band gaps (E g ), respectively. These findings suggest that, particularly when MOFs are nanosized with a large amount of structural disorder, they should no longer be considered “true” single-site catalysts; this is an implicit, but widespread assumption within the MOF-based catalysis field. Implications of these findings will be contrasted with structurally similar metal oxides like TiO 2 and other redox-active MOFs.

Bond dissociation free energy↗
DOE OSTI2022

A theoretical investigation of the effect of Ga alloying on thermodynamic stability, electronic-structure, and oxidation resistance of Ti 2 AlC MAX phase

We present a systematic investigation of thermodynamic stability, phase-reaction, and chemical activity of Al containing disordered Ti 2 (Al-Ga)C MAX phases using machine-learning driven high-throughput framework to understand the oxidation resistance behavior with increasing temperature and exposure to static oxygen. The A-site (at Al) disordering of Ti 2 AlC with Ga shows significant change in the chemical activity of Al with increasing temperature and exposure to static oxygen, which is expected to enable surface segregation of Al, thereby, the formation of Al 2 O 3 and improved oxidation resistance. We performed in-depth convex hull analysis of ternary Ti-Al-C, Ti-Ga-C, and Ti-Al-Ga-C based MAX phase, and provide detailed contribution arising from electronic, chemical and vibrational entropies. The thermodynamic analysis shows change in the Gibbs formation enthalpy (ΔG form ) at higher temperatures, which implies an interplay of temperature-dependent enthalpy and entropic contributions in oxidation resistance Ga doped Ti 2 AlC MAX phases. A detailed electronic structure and chemical bonding analysis using crystal orbital Hamilton population method reveal the origin of change in phases stability and in oxidation resistance in disorder Ti2(Al 1-x Ga x )C MAX phases. Our electronic structure analysis correlate well with the change in oxidation resistance of Ga doped MAX phases. We believe our study provides a useful guideline to understand to role of alloying on electronic, thermodynamic, and oxidation related mechanisms of bulk MAX phases, which can work as a precursor to understand oxidation behavior of twodimensional MAX phases, i.e., MXenes (transition metal carbides, carbonitrides and nitrides).

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tuning the temperature range of superelastic Ni-Ti alloys for elastocaloric cooling via thermal processing

Abstract Caloric cooling enlisting solid-state refrigerants is potentially a promising eco-friendly alternative to conventional cooling based on vapor compression. The most common refrigerant materials for elastocaloric cooling to date are Ni-Ti based superelastic shape memory alloys. Here, we have explored tuning the operation temperature range of Ni 50.8 Ti 49.2 for elastocaloric cooling. In particular, we have studied the effect of thermal treatments (a.k.a. aging) on the transformation temperature, superelasticity, and elastocaloric effects of Ni 50.8 Ti 49.2 shape memory alloy tubes. The isothermal compressive test revealed that the residual strain of thermally-treated Ni-Ti tubes at room temperature approaches zero as aging time is increased. Short-time aging treatment at 400 °C resulted in good superelasticity and elastocaloric cooling performance with a large tunable austenite finish ( A f ) temperature range of 24.7 °C, as determined from the A f temperature of the samples that were aged 5–120 min. The main reason of the property change is the formation of a different amount of Ni 4 Ti 3 precipitates in the NiTi matrix. Our findings show that it is possible to tailor the A f temperature range for development of cascade elastocaloric cooling systems by thermally treating a starting single composition Ni-Ti alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Superconducting phase of Ti x O y thin films grown by molecular beam epitaxy

Here we investigate the complex relationship between the growth conditions and the structural and transport properties of Ti x O y thin films grown by molecular beam epitaxy. Transport properties ranging from metallicity to superconductivity and insulating states are stabilized by effectively tuning the O/Ti ratio via the Ti flux rate and the O partial pressure P Ox for films grown on (0001)-Al 2 O 3 substrates at 850° C. A cubic c-TiO 1±δ buffer layer is formed for low O/Ti ratios, while a corundum cr-Ti 2 O 3 layer is formed under higher-oxidizing conditions. Metallicity is observed for c-TiO 1-δ buffer layers. The superconducting γ -Ti 3 O 5 Magnéli phase is found to nucleate on a c-TiO 1-δ buffer for intermediate POx conditions, and an insulator-superconducting transition is observed at 4.5 K (T$^{onset}_{C}$ = 6K) for 85 nm thick films. Strain relaxation of γ -Ti 3 O 5 occurs with increasing film thickness and correlates with a thickness-dependent increase in T C observed for Ti x O y thin films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Materials Data on Ti(FeO2)3 by Materials Project

Ti(FeO2)3 is beta indium sulfide-derived structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one TiO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.80–2.29 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one TiO6 octahedra, and edges with three FeO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.79–2.21 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six FeO4 tetrahedra, edges with two equivalent TiO6 octahedra, and edges with two FeO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.86–2.10 Å. In the fourth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six FeO4 tetrahedra, edges with two equivalent TiO6 octahedra, and edges with two FeO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.88–2.08 Å. There are twelve inequivalent Fe+2.67+ sites. In the first Fe+2.67+ site, Fe+2.67+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with two TiO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 53–60°. There are a spread of Fe–O bond distances ranging from 1.89–1.99 Å. In the second Fe+2.67+ site, Fe+2.67+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with five TiO6 octahedra and corners with five FeO6 octahedra. The corner-sharing octahedra tilt angles range from 48–66°. There are a spread of Fe–O bond distances ranging from 1.96–2.10 Å. In the third Fe+2.67+ site, Fe+2.67+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with four FeO6 octahedra and corners with five TiO6 octahedra. The corner-sharing octahedra tilt angles range from 48–63°. There are a spread of Fe–O bond distances ranging from 1.86–2.01 Å. In the fourth Fe+2.67+ site, Fe+2.67+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with four TiO6 octahedra and corners with seven FeO6 octahedra. The corner-sharing octahedra tilt angles range from 47–63°. There are a spread of Fe–O bond distances ranging from 1.86–1.99 Å. In the fifth Fe+2.67+ site, Fe+2.67+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with four TiO6 octahedra and corners with five FeO6 octahedra. The corner-sharing octahedra tilt angles range from 50–62°. There are a spread of Fe–O bond distances ranging from 1.93–2.13 Å. In the sixth Fe+2.67+ site, Fe+2.67+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with four TiO6 octahedra and corners with six FeO6 octahedra. The corner-sharing octahedra tilt angles range from 53–60°. There are a spread of Fe–O bond distances ranging from 1.89–2.01 Å. In the seventh Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one FeO6 octahedra, and edges with three TiO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.99–2.24 Å. In the eighth Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, edges with two TiO6 octahedra, and edges with three FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.96–2.16 Å. In the ninth Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one TiO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.12 Å. In the tenth Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one TiO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.11–2.18 Å. In the eleventh Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one FeO6 octahedra, and edges with three TiO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.91–2.10 Å. In the twelfth Fe+2.67+ site, Fe+2.67+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six FeO4 tetrahedra, an edgeedge with one TiO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.99–2.11 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Fe+2.67+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ti4+ and one Fe+2.67+ atom. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.67+ atoms. In the fifth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Ti4+ and two Fe+2.67+ atoms. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Ti4+ and two Fe+2.67+ atoms. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.67+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms. In the tenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.67+ atoms. In the eleventh O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ti4+ and one Fe+2.67+ atom. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to one Ti4+ and two Fe+2.67+ atoms. In the thirteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe+2.67+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms. In the fifteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ti4+ and one Fe+2.67+ atom. In the sixteenth O2- site, O2- is bonded in a distorted trigonal pyramidal geometry to one Ti4+ and three Fe+2.67+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Ti4+ and three Fe+2.67+ atoms. In the eighteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Ti4+ and two Fe+2.67+ atoms. In the nineteenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Ti4+ and three Fe+2.67+ atoms. In the twentieth O2- site, O2- is bonded in a trigonal planar geometry to three Fe+2.67+ atoms. In the twenty-first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms. In the twenty-second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Ti4+ and three Fe+2.67+ atoms. In the twenty-third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms. In the twenty-fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ti4+ and two Fe+2.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Comparative study of helium bubbles in a Ti-Ta alloy and a Ti/Ta nanocomposite

Here, we investigated the size, density, and distribution of helium (He) bubbles in a Ti-Ta single-phase alloy and a Ti/Ta dual-phase nanocomposite using transmission electron microscopy. The Ti/Ta nanocomposite was fabricated via phase separation during high-temperature annealing of the single-phase Ti-Ta alloy. He ion implantation in the Ti-Ta single-phase alloy leads to the formation of nano-scale He bubbles (~1.7 nm in size, ~2.6×10 5 /μm 3 in volumetric density). He bubbles were found to segregate to grain boundaries. Under identical implantation conditions, numerous He bubbles also formed in the Ti/Ta nanocomposite. Closer inspection revealed that He bubbles in the Ti-rich phase are smaller and of higher volumetric density (~1.2 nm, ~8.4×10 5 /μm 3 ) than those in the Tarich phase (~3 nm, ~1.8×10 5 /μm 3 ) and the single-phase alloy. He bubbles were also observed to decorate phase boundaries, but they were generally smaller than those on grain boundaries. These results suggest that Ti/Ta phase boundaries are less conducive to the growth of large He bubbles than grain boundaries in the Ti-Ta single phase alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti by Materials Project

Ti is Magnesium structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ti is bonded to twelve equivalent Ti atoms to form a mixture of corner, edge, and face-sharing TiTi12 cuboctahedra. There are six shorter (2.88 Å) and six longer (2.93 Å) Ti–Ti bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti by Materials Project

Ti is Copper structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ti is bonded to twelve equivalent Ti atoms to form a mixture of corner, edge, and face-sharing TiTi12 cuboctahedra. All Ti–Ti bond lengths are 2.91 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti by Materials Project

Ti is Tungsten structured and crystallizes in the cubic Im-3m space group. The structure is three-dimensional. Ti is bonded in a distorted body-centered cubic geometry to eight equivalent Ti atoms. All Ti–Ti bond lengths are 2.82 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Compositional Modifications to Alter and Suppress Laves Phases in Al x CrMoTa y Ti Alloys

The development of refractory complex concentrated alloys in the Al–Cr–Mo–Ta–Ti alloy system is reported. Alloys with modified Al and Ta concentrations are designed using CALPHAD tools and produced via arc melting and characterized in both as-cast and annealed forms. Properties of the alloys, nature of the microstructures, and phase transformation behavior are described via X-ray diffraction, microstructural characterization, microhardness, and differential scanning calorimetry. Two alloys, namely, Al 0.25 CrMoTa 0.8 Ti and Al 0.75 CrMoTa 0.8 Ti, are represented by a body-centered-cubic matrix phase after annealing, along with a secondary Cr–Ta Laves phase of the C15 and C14 polytypes, respectively. In as-cast and annealed forms, the Al 0.75 CrMoTa 0.45 Ti alloy comprises a single-bcc phase. Microhardness of the Laves phase containing alloys demonstrates susceptibility to cracking, whereas the Al 0.75 CrMoTa 0.45 Ti alloy displays high specific hardness, signs of ductility as evidenced by slip traces near indentations, and minimal scatter of hardness values.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhancing Charge Storage of Mo 2 Ti 2 C 3 MXene by Partial Oxidation

Abstract Driving the pseudocapacitive redox intercalation in 2DMXenes with neutral electrolytes is important for safer, more sustainable, and improved electrochemical charge storage. Single transition metal MXenes, such as Ti 3 C 2 , have shown great promise for energy storage, owing to their high conductivity and redox activity. Mixed metallic MXenes, such as out‐of‐plane ordered Mo 2 Ti 2 C 3 , have remained underexplored in energy storage because of the absence of redox activity in most of the electrolytes. Simultaneous structural modifications and instigating intercalation pseudocapacitance in neutral electrolytes could be a viable strategy for enhancing their electrochemical properties. Herein, a facile synthesis of partially oxidized Mo 2 Ti 2 C 3 MXene (PO‐Mo 2 Ti 2 C 3 ) exhibiting improved charge storage capability is demonstrated. Optical, structural, and spectroscopic analyses indicate the formation of oxide nanostructures upon thermal oxidation of Mo 2 Ti 2 C 3 . This leads to an enhanced energy storage capability with remarkably improved cyclability as well as a high Coulombic efficiency in a neutral LiCl electrolyte. This work highlights the importance of structural modifications of MXenes to enhance their charge storage and shows the promise of less explored double transition metal MXenes in energy storage.

Chemistry↗
DOE OSTI2021

A high-pressure Raman study of FeTiO 3 ilmenite: Fermi resonance as a manifestation of Fe-Ti charge transfer

In this work, we investigated the 300 K high-pressure behavior of ilmenite using Raman spectroscopy to 54 GPa. Upon compression, we observe a Fermi resonance between the lowest frequency A g symmetry peaks (ν 4 and ν 5 ) between ~ 10 and ~ 30 GPa: bands that involve major components of Ti–O and Fe–O-related displacements, respectively. The peaks’ relative intensities switch at ~ 18 GPa and they also reach their minimum separation at ~ 20 GPa, indicating that their maximum resonance occurs between 18 and 20 GPa. The negative shift of the Ti–O-associated ν 4 vibration under compression is fully consistent with a shift in valence of Ti from 4 + to 3 + under compression. Anomalously small mode shifts of other, more localized vibrations are also consistent with a charge transfer from Fe to Ti under compression. At higher pressures, we have not found definitive evidence for a transition to the perovskite-structure at 300 K, which has been well characterized at high pressures and temperatures. At 40 GPa, we observe an apparent reversible disordering that persists up to our highest pressure. The 300 K mode shifts of the Raman active modes in FeTiO 3 under pressure are notably different from those of other ABO 3 compounds (where A = Mg, Mn and B = Ti, Si); in other ilmenite-structured compounds, the peaks shift at a faster rate and there has not been any observation of Fermi resonance. Thus, iron’s complex electronic structure, and its charge transfer with titanium, appears to play a primary role in the behavior of phonons in FeTiO 3 ilmenite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Variation of the Passive Film on Compositionally Concentrated Dual-Phase Al 0.3 Cr 0.5 Fe 2 Mn 0.25 Mo 0.15 Ni 1.5 Ti 0.3 and Implications for Corrosion

The passive film on a dual-phase Al 0.3 Cr 0.5 Fe 2 Mn 0.25 Mo 0.15 Ni 1.5 Ti 0.3 FCC + Heusler (L2 1 ) compositionally concentrated alloy formed during extended exposure to an applied potential in the passive range in dilute chloride solution was characterized. Each phase, with its own distinct composition of passivating elements, formed unique passive films separated by a heterophase interface. High-resolution, surface sensitive characterization enabled chemical analysis of the passive film formed over individual phases. The film formed over the L2 1 phase had a higher concentration of Al, Ni, and Ti, while the film formed over FCC phase was of similar thickness but contained comparatively higher Cr, Fe, and Mo concentrations, consistent with the differences in bulk microstructure composition. The passive film was continuous across phase boundaries and the distribution of passivating elements (Al, Cr, and Ti) indicated both phases were independently passivated. Spatially resolved analysis of the surface chemistry of the dual-phase CCA revealed that the cation with the highest composition in passive film formed on the FCC phase was Cr (52.4 at. pct) and for the L2 1 phase was Ti (53.1 at. pct) despite the bulk concentration of each element being below 20 at. pct in their respective phases. Al, Cr, and Ti were enriched in both phases within the passive film relative to their respective bulk compositions. In parallel studies, single-phase alloys with compositions representative of the FCC and L2 1 phases were synthesized to evaluate the corrosion behavior of each phase in isolation. The corrosion behavior of the dual-phase alloy showed passivity evidenced by a pitting potential of 0.615 V SCE in 0.01 M NaCl. The pitting potential and other electrochemical parameters suggested a combination of behaviors of both single-phase samples, suggesting that the global corrosion behavior may be represented by a composite theory applied to phases, their area fractions, and interphase length. However, the interphase in the dual-phase CCA was a local corrosion initiation site and may limit localized corrosion protectiveness. The alloy design implications for optimization of second phase structure and morphology are discussed.

36 MATERIALS SCIENCE↗