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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A disordered rock salt anode for fast-charging lithium-ion batteries

Rechargeable lithium-ion batteries with high energy density that can be safely charged and discharged at high rates are desirable for electrified transportation and other applications. However, the sub-optimal intercalation potentials of current anodes result in a trade-off between energy density, power and safety. In this paper we report that disordered rock salt Li 3+ x V 2 O 5 can be used as a fast-charging anode that can reversibly cycle two lithium ions at an average voltage of about 0.6 volts versus a Li/Li + reference electrode. The increased potential compared to graphite reduces the likelihood of lithium metal plating if proper charging controls are used, alleviating a major safety concern (short-circuiting related to Li dendrite growth). In addition, a lithium-ion battery with a disordered rock salt Li 3 V 2 O 5 anode yields a cell voltage much higher than does a battery using a commercial fast-charging lithium titanate anode or other intercalation anode candidates (Li 3 VO 4 and LiV 0.5 Ti 0.5 S 2 ). Further, disordered rock salt Li 3 V 2 O 5 can perform over 1,000 charge–discharge cycles with negligible capacity decay and exhibits exceptional rate capability, delivering over 40 per cent of its capacity in 20 seconds. We attribute the low voltage and high rate capability of disordered rock salt Li 3 V 2 O 5 to a redistributive lithium intercalation mechanism with low energy barriers revealed via ab initio calculations. This low-potential, high-rate intercalation reaction can be used to identify other metal oxide anodes for fast-charging, long-life lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2019

Lattice disorder effect on magnetic ordering of iron arsenides

This study investigates magnetic ordering temperature in nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to potential local lattice variations that calculations may not account for. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Néel temperature (T N ) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe 2 As 2 crystal, which is a ‘122’ parent of iron arsenide superconductors, is found through synthesis to have ordering below T N = 195 K (for the locally disordered crystal) or T N = 175 K (for the ordered crystal). In the higher T N crystals, there are shorter planar Fe-Fe bonds [2.7692(2) Å vs. 2.7745(3) Å], a randomized in-plane defect structure, and diffuse scattering along the [00 L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower T N crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger T N and a higher superconducting temperature (T c ) upon the application of pressure. First-principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Direct observation of magnetic ordering induced via systematic lattice disorder in artificial rhombus spin ices

It is critical to understand the effect of lattice geometry on the order parameter of a condensed matter system, as it controls phase transitions in such systems. Artificial spin ices (ASIs) are two-dimensional lattices of Ising-like nanomagnets that provide an opportunity to explore such phenomena by lithographically controlling the lattice geometry to observe its influence on magnetic ordering and frustration effects. Here we report a systematic approach to studying the effects of disorder in rhombus ASIs generated from combinations of five vertex motifs. We investigate four geometries characterized by a geometric order parameter, with symmetries ranging from periodic to quasiperiodic to random. Lorentz transmission electron microscopy data indicates magnetic domain behavior depends on chains of strongly-coupled islands in the periodic and sixfold-twinned lattices, while the behavior of the disordered lattice is dominated by vertex motifs with large configurational degeneracy. Utilizing micromagnetic simulations, a quantitative analysis of the lattice energetics showed that the experimental rotationally-demagnetized state of the disordered ASI was closer in energy to the idealized ground state compared to other periodic and twinned ASIs. Finally, our work provides a unique pathway for using degeneracy, magnetic frustration, and order to control the magnetization behavior of designer disordered systems.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spin susceptibility, upper critical field, and disorder effect in $j = \frac{3}{2}$ superconductors with singlet–quintet mixing

Recently, a new pairing state with the mixing between the s-wave singlet channel and the isotropic d-wave quintet channel induced by centrosymmetric spin–orbit coupling has been theoretically proposed in the superconducting materials with $j = \frac{3}{2}$ electrons [J. Yu and C.-X. Liu, Phys. Rev. B 98, 104514 (2018)]. In this article, we derive the expressions of the zero-temperature spin susceptibility, the upper critical field close to the zero-field critical temperature T c , and the critical temperature with weak random non-magnetic disorders for the singlet–quintet mixed state based on the Luttinger model. Our study reveals the following features of the singlet–quintet mixing. (1) The zero-temperature spin susceptibility remains zero for the singlet–quintet mixed state if only the centrosymmetric spin–orbit coupling is taken into account and deviates from zero when the non-centrosymmetric spin–orbit coupling is introduced. (2) The singlet–quintet mixing can help enhance the upper critical field roughly because it can increase T c . (3) Although the quintet channel is generally suppressed by the non-magnetic disorder scattering, we find the strong mixing between singlet and quintet channels can help to stabilize the quintet channel. As a result, we still find a sizable quintet component mixed into the singlet channel in the presence of weak random non-magnetic disorders. Our work provides the guidance for future experiments on spin susceptibility and upper critical field of the singlet–quintet mixed superconducting states and illustrates the stability of the singlet–quintet mixing against the weak random non-magnetic disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Ice, glass, and solid phases in artificial spin systems with quenched disorder

We present a numerical study on a disordered artificial spin-ice system, which interpolates between the long-range ordered square ice and the fully degenerate shakti ice. Starting from the square-ice geometry, disorder is implemented by adding vertical/horizontal magnetic islands to the center of some randomly chosen square plaquettes of the array at different densities. When no island is added, we have ordered square ice. When all square plaquettes have been modified, we obtain shakti ice, which is disordered yet in a topological phase corresponding to the Rys F-model. In between, geometrical frustration due to these additional center spins disrupts the long-range Ising order of square ice, giving rise to a spin-glass regime at low temperatures. The artificial spin system proposed in our work provides an experimental platform to study the interplay between quenched disorder and geometrical frustration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Embracing disorder in quantum materials design

Many of the most exciting materials discoveries in fundamental condensed matter physics are made in systems hosting some degree of intrinsic disorder. While disorder has historically been regarded as something to be avoided in materials design, it is often of central importance to correlated and quantum materials. This is largely driven by the conceptual and theoretical ease to handle, predict, and understand highly uniform systems that exhibit complex interactions, symmetries, and band structures. In this Perspective, we highlight how flipping this paradigm has enabled exciting possibilities in the emerging field of high entropy materials, focusing primarily on high entropy oxide and chalcogenide quantum materials. These materials host high levels of cation or anion compositional disorder while maintaining unexpectedly uniform single crystal lattices. The diversity of atomic scale interactions of spin, charge, orbital, and lattice degrees of freedom are found to emerge into coherent properties on much larger length scales. Thus, altering the variance and magnitudes of the atomic scale properties through elemental selection can open new routes to tune global correlated phases, such as magnetism, metal–insulator transitions, ferroelectricity, and even emergent topological responses. The strategy of embracing disorder in this way provides a much broader pallet from which functional states can be designed for next-generation microelectronic and quantum information systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

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

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

fuel-cell catalysts↗
DOE OSTI2025

The Frequency Shift and $Q$ of Disordered Superconducting RF Cavities

Niobium superconducting radio-frequency (SRF) cavities for high-energy accelerator applications have been greatly improved in terms of the quality factor $Q$ by techniques such as Nitrogen doping. However, the mechanisms leading to improvement in $Q$ are still not fully understood. Quite recently the SRF group at Fermilab measured anomalies in the frequency shift of N-doped SRF Niobium cavities near the transition temperature. Here we report our theoretical analysis of these results based on the microscopic theory of superconductivity that incorporates anisotropy of the superconducting gap and inhomogeneous disorder in the screening region of the SRF cavities. We are able to account for frequency shift anomalies very close to $T_c$ on the order of fractions of 1 kHz. Our results for the frequency shift and Q are in good agreement with the experimental data reported for all four N-doped Nb SRF cavities by Bafia et al. We also compare our theory with an earlier report on a Nb sample measured at 60 GHz. In addition, we show that the quality factor calculated theoretically has a peak of upper convexity with the largest $Q$ at intermediate levels of disorder. For strong disorder, i.e. the dirty limit, pair breaking in the presence of disorder and screening currents limits the $Q$.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Effects of chemical disorder and spin-orbit coupling on the electronic-structure and Fermi-surface topology of YbSb-based monopnictides

Here, in this work, we study the influence of disorder on the electronic structure of YbSb—a rare-earth monopnictide featuring a simple rocksalt (B1) crystal structure and a well-defined Fermi-surface topology—by employing first-principles density-functional theory. We focus on chemical disorder introduced through Te and Al doping, selected based on their thermodynamic stability in alloyed configurations, to understand how such perturbations modify the electronic states of YbSb. Our results indicate that Te doping predominantly introduces electronlike states at the 𝑋 and 𝐿 points, while Al doping leads to a suppression of holelike states at Γ, effectively driving the system from a semimetallic state to one characterized by very narrow-gap behavior at Γ. This modulation of the Fermi surface, particularly the reduction of central hole pockets at Γ, plays a central role in altering interpocket scattering—a mechanism critical for tuning quantum transport properties, including superconductivity. This disorder-driven modulation of the Fermi surface, particularly the suppression of central hole pockets at Γ, controls interpocket scattering, which is essential for optimizing quantum transport properties, including superconductivity. Our results show that disorder can be effectively used for engineering band topology, thereby tuning quantum related response through a tailored electronic structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Response of a quantum disordered spin system to a local periodic drive

We consider a one-dimensional spin chain system with quenched disorder and in the presence of a local periodic drive. We study the time evolution of the system in the Floquet basis and evaluate the fidelity susceptibility, which is a measure of how a given state changes under a small perturbation, of states to a weak periodic drive. In this work, we demonstrate that the statistical properties of the fidelity susceptibility over different disorder realizations can be used to identify two phases of the system: (1) the many-body localized phase, in which the susceptibility exhibits long tails while its average value decreases rapidly as disorder increases, and (2) the ergodic phase, in which the susceptibility distribution is narrow and its average value weakly depends on disorder. This distinction in the average value of the susceptibility between the two phases develops readily for systems with ten or more spins. Therefore, recently built networks of qubits subject to a local drive can simulate dynamics of a system in the many-body localization regime. We also show that the spin accumulation speed is correlated with the fidelity susceptibility and can also be used to distinguish the two phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Success and breakdown of the T-matrix approximation for phonon-disorder scattering

Here, we examine the validity of the widely used T-matrix approximation for treating phonon-disorder scattering by implementing an unfolding algorithm that allows simulation of disorder up to tens of millions of atoms. The T-matrix approximation breaks down for low-energy flexure phonons that play an important role in thermal transport in two-dimensional materials. Furthermore, insights are developed into the success of the T-matrix approximation in describing maximally mass disordered systems. To achieve this, the phonon unfolding formalism is generalized to describe mass disorder and strongly nonperturbative features of the spectrum are connected to the Boltzmann quasiparticle picture.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Magnetic order and disorder in a quasi-two-dimensional quantum Heisenberg antiferromagnet with randomized exchange

In this work, we present an investigation of the effect of randomizing exchange coupling strengths in the S = 1 / 2 square lattice quasi-two-dimensional quantum Heisenberg antiferromagnet (QHAF) ( QuinH ) 2 Cu ( Cl x Br 1 - x ) 4 · 2 H 2 O (QuinH = Quinolinium, C 9 H 8 N + ), with 0 ≤ x ≤ 1 . Pulsed-field magnetization measurements allow us to estimate an effective in-plane exchange strength J in a regime where exchange fosters short-range order, while the temperature T N at which long-range order (LRO) occurs is found using muon-spin relaxation, allowing us to construct a phase diagram for the series. We evaluate the effectiveness of disorder in suppressing T N and the ordered moment size, and we find an extended disordered phase in the region 0.4 ≲ x ≲ 0.8 where no magnetic order occurs. The observed critical substitution levels are accounted for by an energetics-based competition between different local magnetic orders. Furthermore, we demonstrate experimentally that the ground-state disorder is driven by quantum effects of the exchange randomness, which is a feature that has been predicted theoretically and has implications for other disordered quasi-two-dimensional QHAFs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Extended nonergodic regime and spin subdiffusion in disordered SU(2)-symmetric Floquet systems

In this work, we explore thermalization and quantum dynamics in a one-dimensional disordered SU(2)-symmetric Floquet model, where a many-body localized phase is prohibited by the non-Abelian symmetry. Despite the absence of localization, we find an extended nonergodic regime at strong disorder where the system exhibits nonthermal behaviors. In the strong disorder regime, the level spacing statistics exhibit neither a Wigner-Dyson nor a Poisson distribution, and the spectral form factor does not show a linear-in-time growth at early times characteristic of random matrix theory. The average entanglement entropy of the Floquet eigenstates is subthermal, although violating an area-law scaling with system sizes. We further compute the expectation value of local observables and find strong deviations from the eigenstate thermalization hypothesis. The infinite-temperature spin autocorrelation function decays at long times as $t^{–β}$ with $\textit{β}$ < 0.5, indicating subdiffusive transport at strong disorders.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural disorder-driven topological phase transition in noncentrosymmetric BiTeI

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

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Disorder-robust $\textit{p}$-wave pairing with odd-frequency dependence in normal metal–conventional superconductor junctions [plus supplemental information]

We investigate the induced superconducting pair correlations in junctions between a conventional spin-singlet s-wave superconductor and a disordered normal metal. Decomposing the pair amplitude based on its symmetries in the time domain, we demonstrate that the odd-time, or equivalently odd-frequency, spin-singlet p-wave correlations are both significant in size and entirely robust against random nonmagnetic disorder. We find that these odd-frequency correlations can even be generated by disorder. Our results show that anisotropic odd-frequency pairing represent an important fraction of the proximity-induced correlations in disordered superconducting hybrid structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl

We report half-metallic ferromagnets (HMFs) are one of the most promising materials in the field of spintronics due to their unique band structure, consisting of one spin subband having metallic characteristics along with another subband with semiconductor-like behavior. In this work, we report the synthesis of a novel quaternary Heusler alloy—FeMnVAl—and we have studied the structural, magnetic, transport, and electronic properties complemented with first-principles calculations. Among different possible structurally ordered arrangements, the optimal structure is identified by theoretical energy minimization. The corresponding spin-polarized band-structure calculations indicate the presence of a half-metallic ferromagnetic ground state. A detailed and careful investigation of the x-ray diffraction data, Mössbauer spectra, and nuclear magnetic resonance spectra suggests the presence of site disorder between the Fe and Mn atoms in the stable ordered structure of the system. The magnetic susceptibility measurement clearly establishes a ferromagnetic-like transition below ~213 K. The Fe Mössbauer spectrometry measurements suggest that only the Mn spins could be responsible for the magnetic order, which is consistent with our theoretical calculation. Surprisingly, the density-functional-theory calculations reveal that the spin-polarization value is almost immunized (92.4% → 90.4%) from the Mn-Fe structural disorder, even when nonmagnetic Fe and moment-carrying Mn sites are entangled inseparably. The robustness of spin polarization and half-metallicity in the studied FeMnVAl compound comprising structural disorder is thus quite interesting and could provide a new direction to investigate and understand the exact role of disorders on spin polarization in this class of materials, beyond the available knowledge.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Experimental observation of spin glass state in the highly disordered quaternary Heusler alloy FeRuMnGa

The realization of the spin-glass (SG) state in Heusler alloys is very rare despite the presence of inherent structural and elemental disorder in those compounds. Although a few half- and full-Heusler alloys are known to exhibit the SG state, there is hardly any manifestation of the same in cases of quaternary Heusler compounds. Here we report the observation of a SG state in a highly disordered equiatomic quaternary Heusler compound: FeRuMnGa where the SG state is in between the canonical SG and the cluster glass. Different intricate features of the SG state including nonequilibrium magnetic dynamics at low temperatures in the compound are unveiled through our comprehensive magnetic, heat capacity, and neutron-diffraction studies. Further the structural disorder in the sample is neither conventional A2 - nor B2 -type whereas those two types are commonly observed for Heusler compounds. The presence of disorder also plays a significant role in electron transport properties of the alloy, which is reflected in its exhibition of semimetallic behavior and anomalous Hall effect at low temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

High spin polarization in the disordered quaternary Heusler alloy FeMnVGa

Here in this paper, we report the successful synthesis of a Fe-based highly spin-polarized quaternary Heusler alloy FeMnVGa and its structural, magnetic, and transport properties probed through different experimental methods and theoretical techniques. Density functional theory (DFT) calculations performed on different types of structures reveal that the structure with Ga at 4a, V at 4b, Mn at 4c, and Fe at 4d (space group F$\bar{4}$3m) possess minimum energy among all the ordered variants. Ab initio simulations in the most stable ordered structure show that the compound is a ferromagnet having a large spin-polarization (89.9%). Neutron diffraction reveals that the compound crystallizes in disordered type-2 structure (space group Fm$\bar{3}$m) in which Ga occupies at 4a, V 4b and Fe/Mn occupy 4c/4d sites with 50:50 proportions. The structural disorder is further confirmed by x-ray diffraction, extended x-ray absorption fine structure, 57 Fe Mössbauer spectrometry results, and DFT calculations. Magnetization studies suggest that the compound orders ferromagnetically below T C ~ 293 K and the saturation magnetization follows the Slater-Pauling rule. Mössbauer spectrometry, along with neutron diffraction, suggest that Mn is the major contributor to the total magnetism in the compound, consistent with the theoretical calculations, which also indicates that spin polarization remains high (81.3%), even in the presence of such large atomic disorder. The robustness of the half-metallic ferromagnetic (HMF) property in the presence of disorder is a quite unique characteristic over other reported HMF in literature and makes this compound quite promising for spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗