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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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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Emergent and robust ferromagnetic-insulating state in highly strained ferroelastic LaCoO 3 thin films

Transition metal oxides are promising candidates for the next generation of spintronic devices due to their fascinating properties that can be effectively engineered by strain, defects, and microstructure. An excellent example can be found in ferroelastic LaCoO 3 with paramagnetism in bulk. In contrast, unexpected ferromagnetism is observed in tensile-strained LaCoO 3 films, however, its origin remains controversial. Here we simultaneously reveal the formation of ordered oxygen vacancies and previously unreported long-range suppression of CoO 6 octahedral rotations throughout LaCoO 3 films. Supported by density functional theory calculations, we find that the strong modification of Co 3d-O 2p hybridization associated with the increase of both Co-O-Co bond angle and Co-O bond length weakens the crystal-field splitting and facilitates an ordered high-spin state of Co ions, inducing an emergent ferromagnetic-insulating state. Our work provides unique insights into underlying mechanisms driving the ferromagnetic-insulating state in tensile-strained ferroelastic LaCoO 3 films while suggesting potential applications toward low-power spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Unprecedented lattice volume expansion on doping stereochemically active Pb 2+ into uniaxially strained structure of CaBa 1- x Pb x Zn 2 Ga 2 O 7

Lone pair cations like Pb 2+ are extensively utilized to modify and tune physical properties, such as nonlinear optical property and ferroelectricity, of some specific structures owing to their preference to adopt a local distorted coordination environment. Here we report that the incorporation of Pb 2+ into the polar “114”-type structure of CaBaZn 2 Ga 2 O 7 leads to an unexpected cell volume expansion of CaBa 1- x Pb x Zn 2 Ga 2 O 7 (0 ≤ x ≤ 1), which is a unique structural phenomenon in solid state chemistry. Structure refinements against neutron diffraction and total scattering data and theoretical calculations demonstrate that the unusual evolution of the unit cell for CaBa 1- x Pb x Zn 2 Ga 2 O 7 is due to the combination of the high stereochemical activity of Pb 2+ with the extremely strained [Zn 2 Ga 2 O 7 ] 4- framework along the c -axis. The unprecedented cell volume expansion of the CaBa 1- x Pb x Zn 2 Ga 2 O 7 solid solution in fact is a macroscopic performance of the release of uniaxial strain along c -axis when Ba 2+ is replaced with smaller Pb 2+ .

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

Flame dynamics and kinetic coupling of ammonia and dimethyl-ether in non-premixed cool and warm flames at elevated pressure

Developing advanced low-temperature combustion engines with ammonia-biofuel blends requires a comprehensive understanding of low-temperature flame dynamics and kinetic interactions between ammonia and oxygenated fuels at elevated pressures. This work aims to study the dynamics and kinetics of non-premixed Dimethyl Ether (DME)/Ammonia (NH 3 ) cool and warm flames, and their reignition to hot flames. A counterflow burner is employed to establish DME/NH 3 cool/warm flames at pressures up to 5 atm. The extinction limits of cool flame and the reignition limits of warm flame to hot flame are measured by varying NH 3 concentrations and compared to simulations to quantitatively examine the effects on DME/NH 3 flames. It is found that NH 3 inhibits low-temperature DME oxidation and results in lower cool flame extinction limits. Warm flames in the presence of NH 3 are observed for the first time, revealing a non-monotonic effect of NH 3 addition: a small amount of NH 3 presence enhances warm flame chemistry and promotes reignition to hot flames, while a high NH 3 concentration weakens the warm flame. This trend is further explained by 0-D PSR kinetic simulations and 1-D S-curve flame dynamic calculations. Three flame transition regimes between cool flames (CF), warm flames (WF), and hot flames (HF) by different levels of NH 3 additions at a specific strain rate are identified, namely WFHF reignition, WF-CF transition, and WF extinction. Reaction sensitivity analyses of OH at low temperatures show that NH3 inhibits DME oxidation through OH consumption via H-abstraction and the kinetic couplings of RO 2 /NH 2 , RO 2 /NO x , R/NO x , and O 2 QOOH/NO x further suppress the low-temperature branching. At intermediate-temperatures, NH 2 /NO x /HO 2 coupling promotes warm flames via the pathway NH 2 → H 2 NO → HNO → NO by converting O 2 → HO 2 → OH. At even higher NH₃ concentrations, radical termination reactions of NH 2 + NO/NO 2 and excessive OH consumption via H-abstraction inhibit the flame. The insights into the kinetic coupling between NH 3 and low-temperature chemistry at elevated pressure and its impact on the dynamics of cool-warm-hot flame transitions will contribute to advancing combustion technologies with reduced emissions and improved energy-efficiency.

42 ENGINEERING↗
DOE OSTI2024

Zero-strain high entropy spinel oxide (FeNiCuCrMn) 3 O 4 @rGO as high-performance anode for sodium ion battery

High entropy spinel oxides (HEOs), as a new type of anode material with at least five transition metal elements and high theoretical specific capacity, have enormous promise in sodium ion batteries (SIBs). However, the influence of different transition metal elements on the structure and electrochemical performances of HEOs is not clear. Here, in this study, the addition of Mn to HEO can increase the surface oxygen vacancy (O v ) concentration, shorten the band gap, and enhance the electrochemical performance of (FeNiCuCrMn) 3 O 4 @rGO. XPS results show (FeNiCuCrMn)3O4@rGO has the highest surface O v concentration. Ab initio calculations demonstrate that the indirect band gap of (FeNiCuCrMn)3O4@rGO is 0.068 eV. In situ X-ray diffraction and synchrotron X-ray absorption spectroscopy reveal that (FeNiCuCrMn) 3 O 4 @rGO exhibits a zero-strain characteristic with an inconsequential unit cell volume change of 0.2 %. Specifically, (FeNiCuCrMn) 3 O 4 @rGO as anode materials for SIBs show good cyclic stability (with a capacity retention of 84 % at 500 mA g −1 after 3000 cycles). Overall, this work provides a new direction for optimizing transition metal elements in HEOs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Composition dependence of atomic order in strain-relaxed, metastable GeSn alloys

Extended x-ray absorption fine structure (EXAFS) measurements of single-crystal Ge/GeSn radial heterostructure nanowires are used to examine the effects of composition on both short-range order (SRO) and longer-range disorder in GeSn alloys. GeSn has prompted significant interest because it can achieve a direct band gap for sufficient Sn concentrations beyond the equilibrium solid solubility limit in an all-group IV system. Short-range order in this material is particularly interesting as it has been predicted to affect the band gap independent of average composition or strain effects. By independently controlling the Sn composition and GeSn thickness during chemical vapor deposition of misfitting GeSn shells around ultrathin, elastically compliant, Ge core nanowires, the elastic misfit strain in the GeSn is minimized for Sn compositions over the studied range ≈Ge 0.96 Sn 0.04 to Ge 0.88 Sn 0.12 . The degree of SRO was found to decrease with increasing Sn composition. Additionally, damping of the EXAFS signal was observed as the Sn content increased, particularly for increasingly distant atomic shells about the absorbing atom, even for scattering paths not involving Sn atoms. This result is quantified as an increase in the mean-squared relative displacement parameters of the shells. These measurements reveal the accommodation of local strain due to the presence of the highly size-mismatched Sn atoms in the Ge diamond cubic lattice (≈14%), which may have effects on the band structure of the material in addition to the influence of short-range atomic order. Comparison among the nanowire samples allows for calculation of the topological rigidity parameter, a ∗∗ , for the first-neighbor bond lengths. Furthermore, these exhibit chemically distinct values for Ge-Ge, Ge-Sn, and Sn-Sn, and they are consistent with the value a ∗∗ = 0.75 ± 0.07 confirming the general applicability of the model to alloys with both large amounts of natural misfit strain and the potential for short-range order.

Crystal structure Semiconductors Transmission elec↗
DOE OSTI2023

Eulerian finite element implementations of a dislocation density-based continuum model

In Eulerian finite element simulations, the mesh moves relative to the material. After every change of position between the mesh and the material, the state variables are interpolated to the new mesh position, which is referred to as advection. Large strain crystal plasticity models are based on the multiplicative decomposition of the total deformation gradient. Further, the stress is evaluated as a function of the thermoelastic strain, temperature, and other state variables. Advection of tensor quantities, such as the strain, is coupled with possibly significant advection errors. In an effort to reduce the advection errors, we develop two rate forms of an established dislocation density-based continuum model. To that end, we replace the multiplicative decomposition of the deformation gradient with the additive decomposition of the velocity gradient, and define the stress rate instead of the total stress. The Eulerian implementation is compared with Lagrangian calculations, and two numerical examples with severe deformation levels are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Site-Controlled Quantum Emitters in Monolayer MoSe 2

Atomically thin semiconductors provide a highly attractive platform for quantum emitters (QEs): They can be combined with arbitrary substrates, can be spatially aligned with photonic structures, and can be electrically driven. All QEs reported to date in these materials have, however, relied on nominally spin-forbidden transitions, with radiative rates falling substantially below those of other solid-state QE systems. In this work, we employ strain confinement in monolayer MoSe 2 to produce engineered QEs, as confirmed in photon antibunching measurements. We discuss spin-allowed versus spin-forbidden transitions based on magneto- and time-resolved photoluminescence measurements. We calculate a radiative rate for spin-allowed quantum emission greater than 1 ns –1 , which exceeds reported radiative rates of WSe 2 QEs by 2 orders of magnitude.

2D materials↗
DOE OSTI2025

Strained-Induced Morphological Reconstruction of RuO 2 (110) Thin-Film Electrocatalysts

Strain is a widely used strategy for electrocatalyst engineering. Overstraining, however, can lead to unintentional materials transformation. We investigate the impact of strain on the surface morphology of a rutile RuO 2 (110) film grown on a symmetry-matching rutile TiO 2 (110) substrate. When the film thickness exceeds 9 nm, the RuO 2 surface relaxes by forming step edges that expose the {011} plane. Density functional theory (DFT) calculation shows that the (011) facet is among the lower energy surfaces of rutile RuO 2 , suggesting that this formation incurs minimal energetic penalties. In situ atomic force microscopy (AFM) shows that the film maintains the (110) structure of the terrace during electrochemistry. Inductively coupled plasma–mass spectrometry (ICP-MS) further reveals the insensitivity of the Ru dissolution to strain. Here, our findings show a strain-relieving pathway via surface reconstruction in RuO 2 (110) and provide an example of a strain-relieving mechanism that does not affect dissolution.

Evolution reactions↗
DOE OSTI2020

Eigenfrequency constrained topology optimization of finite strain hyperelastic structures

This paper incorporates hyperelastic materials, nonlinear kinematics, and preloads in eigenfrequency constrained density–based topology optimization. The formulation allows for initial finite deformations and subsequent small harmonic oscillations. The optimization problem is solved by the method of moving asymptotes, and the gradients are calculated using the adjoint method. Both simple and degenerate eigenfrequencies are considered in the sensitivity analysis. A well-posed topology optimization problem is formulated by filtering the volume fraction field. Numerical issues associated with excessive distortion and spurious eigenmodes in void regions are reduced by removing low volume fraction elements. The optimization objective is to maximize stiffness subject to a lower bound on the fundamental eigenfrequency. Numerical examples show that the eigenfrequencies drastically change with the load magnitude, and that the optimization is able to produce designs with the desired fundamental eigenfrequency.

42 ENGINEERING↗
DOE OSTI2025

Intrinsic property of defective β-Ga 2 O 3 to self-heal under ionizing irradiation

Damage evolution and phase stability in defective β-Ga 2 O 3 and an irradiation-converted γ-Ga 2 O 3 layer have been studied under ionizing irradiation at 300 K. By exploring athermal nonequilibrium processes in β-Ga 2 O 3 , we succeed in identifying a self-healing mechanism that enables recovery pre-existing damage, characterized by a recovery cross-section of ~0.17 nm 2 . Remarkably, this study further demonstrates that the crystallinity of the irradiation-converted γ-Ga 2 O 3 layer improves under ionizing irradiation. More importantly, X-ray diffraction analysis reveals that the highly-strained 𝛾 -phase transforms into a highly-crystalline structure without film disintegration, contrasting to that reported for isochronal annealing at 1000 K. The inelastic thermal spike calculations provide insights into the important effects of energy transfer to electrons in reordering the local atomic arrangement of both defective β- Ga 2 O 3 and 𝛾-Ga 2 O 3 . This behavior suggests a pathway for low-temperature crystallization, offering a promising strategy for fabricating ultrahigh-speed non-volatile memory devices.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Dynamic compression and spallation behavior of NbTaTiVZr high-entropy alloy

High-entropy alloys are a new class of materials with promising properties for aerospace and defense applications. The unique behavior of these materials is driven by the complex interactions between dissimilar atoms in a crystal and requires combined theoretical and experimental efforts to unlock their full potential. Here, we evaluate the relationship between the microstructure and the dynamic response of the equiatomic NbTaTiVZr alloy. Specifically, the shock Hugoniot, or equation of state, was measured up to a particle velocity of 0.5 mm μs −1 using gas gun plate impacts. Shock wave profile and incipient spallation experiments were used to characterize wave propagation and damage formation with post-mortem recovery experiments. Molecular dynamics simulations confirm the experimental findings and extend them up to 2.1 mm μs −1 particle velocity. Computational thermodynamic calculation of phase diagram simulations explain details of the material microstructure, which explains the measured strength and experimental damage patterns. Overall, this work provides detailed high-strain-rate characterization of a refractory high-entropy alloy, and more importantly, a framework and demonstration of the utility and necessity of a combined theoretical and experimental approach, outlining the importance of considering processing and manufacturing conditions when evaluating the performance of new materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Experimental and theoretical investigation of FeCrVAl and related compounds

Abstract We have carried out a combined theoretical and experimental investigation of FeCrVAl, and the effect of Mn and Co doping on its structural, magnetic, and electronic band properties. Our first principles calculations indicate that FeCrVAl, FeCr 0.5 Mn 0.5 VAl, and FeCr 0.5 Co 0.5 VAl exhibit nearly perfect spin polarization, which may be further enhanced by mechanical strain. At the same time, FeCrV 0.5 Mn 0.5 Al and FeCrV 0.5 Co 0.5 Al exhibit a relatively small value of spin polarization, making them less attractive for practical applications. Using arc melting and high vacuum annealing, we synthesized three compounds FeCrVAl, FeCr 0.5 Mn 0.5 VAl, and FeCr 0.5 Co 0.5 VAl, which are predicted to exhibit high spin polarization. The room temperature x-ray diffraction patterns of all samples are fitted with full B2 type disorder with a small amount of FeO 2 secondary phase. All samples show very small saturation magnetizations at room temperature. The thermomagnetic curves M(T) of FeCrVAl and FeCr 0.5 Co 0.5 VAl are similar to that of a paramagnetic material, whereas that of FeCr 0.5 Mn 0.5 VAl indicates ferrimagnetic behavior with the Curie temperature of 135 K. Our findings may be of interest for researchers working on Heusler compounds for spin-based electronic applications.

Physics↗
DOE OSTI2024

Rapid Design of Cost-Effective Refractory High Entropy Alloys Strengthened by Precipitation

Funded by the ARPA-E ULTIMATE program, this project aims to develop cost-effective refractory high entropy alloys (RHEAs) for gas turbine blades applications at 1300 degree Celsius and above. The alloy design focuses on carbides precipitation strengthening in a strong and ductile solid solution BCC matrix. The goal is to achieve balanced mechanical properties including room temperature ductility & fracture toughness and high temperature strength and creep resistance, while maintaining comparable oxidation resistance and densities to Ni-base superalloys. To accelerate alloy design, multiscale modeling including CALPHAD and first-principles density functional theory (DFT) calculations and machine learning are performed. Specifically, high throughput phase diagram calculations and screening are carried out using CALPHAD; DFT calculations are performed to predict intrinsic ductility, grain boundary strengthening potential, coefficient of thermal expansion (CTE) and temperature-dependent elastic constants. Temperature dependent yield stress, creep strain and CTE are also predicted using machine learning. Down-selected alloys are synthesized in small buttons of about 250g using arc melting for rapid evaluation on microstructure and mechanical properties before employing plasma arc melting and additive manufacturing for producing large ingots. Preliminary computational and experimental results of this project will be presented and future direction in RHEA development will be discussed.

high temperature materials↗
DOE OSTI2021

First-principles study of electron transport in ScN

We investigate the conduction-band structure and electron mobility in rocksalt ScN based on density functional theory. The first-principles band structure allows us to obtain band velocities and effective masses as a function of energy. Electron-phonon scattering is assessed by explicitly computing the q-dependent electron-phonon matrix elements, with the inclusion of the long-range electrostatic interaction. The influence of free-carrier screening on the electron transport is assessed using the random phase approximation. We find a notable enhancement of electron mobility when the carrier concentration exceeds 10 20 cm -3 . We calculate the room-temperature electron mobility in ScN to be 587 cm2 /Vs at low carrier concentrations. When the carrier concentration is increased, the electron mobility starts to decrease significantly around n = 10 19 cm -3 , and drops to 240 cm 2 /Vs at n = 10 21 cm -3 . We also explore the influence of strain in (111)- and (100)-oriented ScN films. For (111) films, we find that a 1.0% compressive epitaxial strain increases the in-plane mobility by 72 cm 2 /Vs and the out-of-plane mobility by 50 cm 2 /Vs. For (100) films, a 1.0% compressive epitaxial strain increases the out-of-plane mobility by as much as 172 cm2 /Vs, but has a weak impact on the in-plane mobility. Our study sheds light on electron transport in ScN at different electron concentrations and shows how strain engineering could increase the electron mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unveiling Structural Heterogeneity and Imbalance of Gold Decahedral Nanoparticles using Four-dimensional Scanning Transmission Electron Microscopy

Multi-twinned structures have been observed in technologically important crystal systems, for example diamond cubic and face-centered cubic (FCC) lattices, that include materials such as diamond, silicon, a wide range of noble metals, and their nanoscale counterparts. Beyond atomic building blocks, the special arrangements also occur in the self-assembly of nanoparticles (NP) and μm-sized colloidal particles and occupy parts of their phase diagrams. Spanning a wide range of length scales, the universality of the structures arises when the systems attempt to achieve multitwinned structures by overcoming geometric misfits during minimizing surface energies with entirely {111} or close-packing facets. While it is fundamental to understand how strain is sustained upon twinned structures and symmetry breaking, the knowledge will be paramount in practical aspects such as guiding and controlling the thin film growth, anisotropic NP growth, and self-assembly of NPs. Au decahedral (Dh) NP, as the most prevalent multi-twinned model system, fits five tetrahedral motifs into a circle by sharing an axis resulting in a geometric misfit angle of 7.35°, or a disclination with power of -7.35°. Postulating how Au FCC lattice adopts the misfit, theoretical models have been developed to address the underlying lattice symmetry and inhomogeneous strain distribution separately. Yet, experimental reports regarding the former have been limited due to the relatively large X-ray beam sizes that do not fit the sizes of NPs. On the other hand, though the latter has been widely adapted in the thermodynamics of small (<10 nm) multi-twinned nanoparticles, previous literature has shown that, at edge length of 17 nm, the theory’s is invalidated by shear strain that is observed in a defect-free Au Dh NP by high-resolution transmission electron microscopy (HR-TEM) imaging. Though the advancement of aberrationcorrected scanning transmission electron microscopy (AC-STEM) imaging and ab initio calculation techniques brings new opportunities, along with challenges in complicated image analysis and limitation in particle size (usually below 10 nm), the gap between nanoscale and mesoscale has never been extended to gain insight from atomic system with straightforward interaction potentials.

4D-STEM↗
DOE OSTI2020

Tuning Fermi Levels in Intrinsic Antiferromagnetic Topological Insulators MnBi 2 Te 4 and MnBi 4 Te 7 by Defect Engineering and Chemical Doping

MnBi 2 Te 4 and MnBi 4 Te 7 are intrinsic antiferromagnetic topological insulators, offering a promising materials platform for realizing exotic topological quantum states. However, high densities of intrinsic defects in these materials not only cause bulk metallic conductivity, preventing the measurement of quantum transport in surface states, but may also affect magnetism and topological properties. In this paper, systematic density functional theory calculations reveal specific material chemistry and growth conditions that determine the defect formation and dopant incorporation in MnBi 2 Te 4 and MnBi 4 Te 7 . The large strain induced by the internal heterostructure promotes the formation of large-size-mismatched antisite defects and substitutional dopants. The results here show that the abundance of antisite defects is responsible for the observed n-type metallic conductivity. Additionally, a Te-rich growth condition is predicted to reduce the bulk free electron density, which is confirmed by experimental synthesis and transport measurements in MnBi 2 Te 4 . Furthermore, Na doping is proposed to be an effective acceptor dopant to pin the Fermi level within the bulk band gap to enable the observation of surface quantum transport. The defect engineering and doping strategies proposed here should stimulate further studies for improving synthesis and for manipulating magnetic and topological properties in MnBi 2 Te 4 , MnBi 4 Te 7 , and related magnetic topological insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2022

An Eulerian crystal plasticity framework for modeling large anisotropic deformations in energetic materials under shocks

Here, this paper demonstrates a novel Eulerian computational framework for modeling anisotropic elastoplastic deformations of organic crystalline energetic materials (EM) under shocks. While Eulerian formulations are advantageous for handling large deformations, constitutive laws in such formulations have been limited to isotropic elastoplastic models, which may not fully capture the shock response of crystalline EM. The present Eulerian framework for high-strain rates, large deformation material dynamics of EM incorporates anisotropic isochoric elasticity via a hypo-elastic constitutive law and visco-plastic single-crystal models. The calculations are validated against atomistic calculations and experimental data and benchmarked against Lagrangian (finite element) crystal plasticity computations for shock-propagation in a monoclinic organic crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7 tetrazocine (β-HMX). The Cauchy stress components and the resolved shear stresses calculated using the present Eulerian approach are shown to be in good agreement with the Lagrangian computations for different crystal orientations. The Eulerian framework is then used for computations of shock-induced inert void collapse in β-HMX to study the effects of crystal orientations on hotspot formation under different loading intensities. The computations show that the hotspot temperature distributions and the collapse profiles are sensitive to the crystal orientations at lower impact velocities (viz., 500 m/s); when the impact velocity is increased to 1000 m/s, the collapse is predominantly hydrodynamic and the role of anisotropy is modest. The present methodology will be useful to simulate energy localization in shocked porous energetic material microstructures and other situations where large deformations of single and polycrystals govern the thermomechanical response.

42 ENGINEERING↗