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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

The NanoSIMS-HR: The Next Generation of High Spatial Resolution Dynamic SIMS

The high lateral resolution and sensitivity of the NanoSIMS 50 and 50L series of dynamic SIMS instruments have enabled numerous scientific advances over the past 25 years. Here, in this study, we report on the NanoSIMS-HR, the first major upgrade to the series, and analytical tests in a suite of sample types, including an aluminum sample containing silicon crystals, microalgae, and plant roots colonized with a symbiotic fungus. Significant improvements have been made in the Cs + ion source, high voltage (HV) control, stage reproducibility, and other aspects of the instrument that affect performance. The modified design of the NanoSIMS-HR thermal-ionization Cs + source enables a 5 pA primary ion beam to be focused into a 100 nm spot, a ~2.5-fold increase compared to Cs + sources on previous instruments (~2 pA at 100 nm). The brightness of the new Cs + source enables an ultimate lateral resolution as high as 30 nm and improved detection limits for a given analysis area. Sample stage movement accuracy is higher than 500 nm, enabling many-fold higher throughput automated analyses. With the new HV control, the primary ion beam impact energy can be reduced from 16 to 2 keV, which enables higher depth resolution during depth profiling (a 2-fold improvement), albeit with a 5-fold decrease in lateral resolution. In the NanoSIMS-HR, the secondary ion column and detection system are identical to those used in the previous series, and the isotopic analysis performance is as precise as in previous NanoSIMS instruments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Open Specy 1.0: Automated (Hyper)spectroscopy for Microplastics

Microplastic spectral analysis is one of the most time-consuming processes in studying microplastic pollution, often requiring days per sample. Researchers are transitioning to automated batch and hyperspectral image analysis techniques to enhance efficiency. Open Specy, initially aimed at manual single-spectrum analysis, has now integrated automated methods. This updated version, Open Specy 1.0, introduces several new features, including two algorithms for automated processing (smoothing and particle compression), an extensive library containing over 40,000 open-source Raman and FTIR spectra, and two machine learning classifiers (logistic regression and k medoids) developed from this library. Furthermore, it includes a revamped user interface, an R package, and a benchmark data set for testing future advancements in automated techniques. Researchers evaluated various configurations for hyperspectral smoothing, particle identification, compression, and splitting, to achieve combined recovery rates between 50 and 150% particle counts, identities, and sizes with a coefficient of variation (CV) of less than 40% (the accredited standard). Mean absorbance times the standard deviation provided a consistent particle identification. Hyperspectral smoothing led to a 96% combined recovery rate and reduced variability (CV = 38%) compared to the 86% recovery (CV = 83%) of nonsmoothed controls. Additionally, compressing spectra for particles was significantly faster (>3x) and showed similar accuracy but with reduced variability than processing each pixel individually. Key challenges persist in automating spectral analysis, particularly in refining particle splitting algorithms, and improving identification routines to minimize false positives and negatives. In conclusion, new methods in sample preparation for better stabilization and dispersion of particles could overcome some of these issues.

13 HYDRO ENERGY↗
DOE OSTI2026

Thermal Gradient Effects on Redox Evolution and Volatility-Driven Fractionation in Ternary U/Ce/Cs Condensates

Understanding how thermal history influences redox evolution and chemical fractionation is essential for characterizing high-temperature condensation in complex materials, including nuclear debris. Here, we tested the hypothesis that distinct thermal regimes in a plasma flow reactor influence redox pathways and elemental partitioning in ternary U/Ce/Cs systems. A configurable plasma flow reactor was modified with an external tube furnace to impose two distinct thermal gradients: continuous ambient cooling and a furnace-assisted thermal hold-up near 1400 K followed by rapid cooling. Transmission electron microscopy characterized phase identity, morphology, and nanoscale element distributions, while inductively coupled plasma-mass spectrometry quantified bulk elemental ratios. Across both thermal regimes, uranium and cerium condensed as UO 2 and CeO 2 as dominant refractory oxide products. Uranium partially oxidized to α-UO 3 during extended ambient cooling, while furnace-assisted hold-up preserved UO 2 and produced partial reduction of cerium to Ce 2 O 3 . Cesium remained volatile upstream and condensed later in the reactor, forming Cs 2 O and Cs-uranate phases with the highest incorporation after thermal hold-up. Bulk ICP-MS measurements supported these observations. U/Ce ratios remained comparatively stable and Cs displayed delayed and apparent transient enrichment that matched the nanoscale measurements. This integrated approach provides a quantitative method for linking thermal gradients to redox evolution and volatility-driven fractionation. These results show how the plasma flow reactor can identify where equilibrium descriptions remain adequate and where kinetic effects from residence time and temperature history must be considered when interpreting condensation behavior in multicomponent systems.

and nuclear chemistry↗
DOE OSTI2026

Position-Specific Carbon Isotope Fingerprinting of Fluorinated Organics and Degradation Products

Fluorinated organic compounds are of growing environmental and forensic relevance due to their widespread use in pharmaceuticals, agrochemicals, and consumer products, their environmental persistence, and potential ecological and human health impacts. Elucidating their sources and transformation pathways is therefore a major focus of current research. Stable carbon isotope analysis provides a powerful approach for tracing molecular origins and linking parent compounds to degradation products. Recent isotope measurements have largely relied on mass-spectrometry techniques, which provide only an average isotope ratio across a compound. In this work, we employ a novel nuclear magnetic resonance (NMR) spectroscopy tool to determine position-specific carbon isotope ratios ( 13 C/ 12 C) in organofluorine compounds and their degradation products. This approach enables isotope measurements without combustion or extensive purification and, crucially, resolves ratios at individual carbon positions rather than bulk averages. The resulting intramolecular isotope fingerprints are unique to a molecule’s source. Applied to selected pharmaceuticals and pesticides, these fingerprints allow discrimination of chemically identical compounds. Moreover, we show that the 13 C/ 12 C signature at the fluorinated carbon persists through degradation, demonstrated for lansoprazole and fipronil. The 19 F NMR data produced for the 13 C/ 12 C analyses are also well suited for impurity profiling, providing an additional dimension for fingerprinting fluorinated organics. These findings suggest that position-specific isotope analysis can serve as part of a broader suite of tools for source characterization of organofluorine compounds and their breakdown derivatives, with potential applications in product validation, forensics, and linking these compounds to their breakdown products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Comparison of the Forward and Reverse Photocycle Dynamics of Two Highly Similar Canonical Red/Green Cyanobacteriochromes Reveals Unexpected Differences

Cyanobacteriochromes (CBCRs) are cyanobacterial photoreceptors that exhibit photochromism between two states: a thermally stable dark-adapted state and a metastable light-adapted state with bound linear tetrapyrrole (bilin) chromophores possessing 15Z and 15E configurations, respectively. The photodynamics of canonical red/green CBCRs have been extensively studied; however, the time scales of their excited-state lifetimes and subsequent ground-state evolution rates widely differ and, at present, remain difficult to predict. Here, we compare the photodynamics of two closely related red/green CBCRs that have substantial sequence identity (~68%) and similar chromophore environments: AnPixJg2 from Anabaena sp. PCC 7120 and NpR6012g4 from Nostoc punctiforme. Using broadband transient absorption spectroscopy on the primary (125 fs to 7 ns) and secondary (7 ns to 10 ms) time scales together with global analysis modeling, our studies revealed that AnPixJg2 and NpR6012g4 have comparable quantum yields for initiating the forward ( 15Z P r → 15E P g ) and reverse ( 15E P g → 15Z P r ) reactions, which proceed through monotonic and nonmonotonic mechanisms, respectively. In addition to small discrepancies in the kinetics, the secondary reverse dynamics resolved unique features for each domain: intermediate shunts in NpR6012g4 and a Meta-Gf intermediate red-shifted from the 15Z P r photoproduct in AnPixJg2. Altogether, this study supports the conclusion that sequence similarity is a useful criterion for predicting pathways of the light-induced evolution and quantum yield of generating primary intermediate Φ p within subfamilies of CBCRs, but more studies are still needed to develop a comprehensive molecular level understanding of these processes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Cofactor Complexes of DesD, a Model Enzyme in the Virulence-related NIS Synthetase Family

The understudied nonribosomal-peptide-synthetase-independent siderophore (NIS) synthetase family has been increasingly associated with virulence in bacterial species due to its key role in the synthesis of hydroxamate and carboxylate "stealth" siderophores. We have identified a model family member, DesD, from Streptomyces coelicolor , to structurally characterize using a combination of a wild-type and a Arg306Gln variant in apo , cofactor product AMP-bound, and cofactor reactant ATP-bound complexes. The kinetics in the family has been limited by solubility and reporter assays, so we have developed a label-free kinetics assay utilizing a single-injection isothermal-titration-calorimetry-based method. We report second-order rate constants that are 50 times higher than the previous estimations for DesD. Our Arg306Gln DesD variant was also tested under identical buffer and substrate conditions, and its undetectable activity was confirmed. These are the first reported structures for DesD, and they describe the critical cofactor coordination. This is also the first label-free assay to unambiguously determine the kinetics for an NIS synthetase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Lithium thiostannate spinels: air-stable cubic semiconductors.

Lithium chalcogenide materials have been studied less than other alkali metal analogs and are of interest as ion conductors and semiconductors capable of thermal neutron detection. Herein, we describe the structural, thermal, magnetic, electronic, and ionic properties of a new family of cubic lithium thiospinels Li2MSn3S8 (M = Mg, Fe, Mn, Ni, Co) and Li1.66CuSn3.33S8. All compounds crystallize in the Fd (3) over barm space group and exhibit site occupancy disorder with Sn and M on the octahedral site for M = Mg, Fe, Mn, Ni, Co. The Li1.66CuSn3.33S8 compound also exhibits occupancy disorder on the tetrahedral sites between Li and Cu, as well as on the octahedral sites between Li and Sn. We demonstrate the ability to tune the physical properties of the compounds by changing their composition. By tuning the identity of the transition metal in the structure, the optical band gaps can vary between 0.91(2) and 2.19(2) eV, and electrical resistivities between 2.8 x 10(3) Omega-cm and 2.2 x 10(7)Omega-cm can be achieved. Density functional theory calculations for Li2MgSn3S8 and Li1.66CuSn3.33S8 suggest that both materials have indirect band gaps and significantly dispersive conduction bands. A bandwidth dispersion of 0.75 and 0.70 eV along the Gamma -> M direction in the conduction band are predicted for Li2MgSn3S8 and Li1.66CuSn3.33S8, respectively, with an electron effective mass of 0.49 and 0.55 m(e) at the Gamma point. The hole effective mass in the valence band is calculated to be 1.25 me at the M point and 0.75 me at the L point for Li2MgSn3S8 and Li1.66CuSn3.33S8, respectively. The ionic/electronic conductivity of each compound was determined using AC electrochemical impedance spectroscopy.

Quintero, Michael A.↗
DOE OSTI2021

Lowering the Activation Barriers for Lithium-Ion Conductivity through Orientational Disorder in the Cyanide Argyrodite Li6PS5CN

Rapid advancements in safe and high-energy-density energy storage are predicated on identifying new solid-state ion conductors with low activation energies and high ionic conductivities for all-solid-state battery technologies. Halide argyrodites are among some of the top candidates for solid-state electrolytes, as they can achieve ionic conductivities that approach liquid electrolytes. Incorporating dynamic pseudohalide species in argyrodite solid electrolytes presents an exciting opportunity to exploit lattice dynamics as a design principle to modulate the ion conduction properties of solid-state ion conductors. In the present study, we have prepared the new argyrodite Li 6 PS 5 CN containing orientationally disordered cyanide ions. The new cyanide argyrodite Li 6 PS 5 CN exhibits an activation barrier to Li-ion transport of 471 ± 25 meV and a room-temperature ionic conductivity of 6(2) × 10 –5 S cm –1 in comparison to the activation barrier of 502 ± 16 meV and an ionic conductivity of 2.3(1) × 10 –4 S cm –1 measured for the bromide analogue Li 6 PS 5 Br. Structural studies of both compounds by high-resolution X-ray diffraction indicate that Li 6 PS 5 CN and Li 6 PS 5 Br adopt nearly identical crystal structures with similar lattice parameters, which indicates that lower activation barriers in Li 6 PS 5 CN arise due to the cyanide ion itself rather than due to changes in the geometry of conduction pathways in the local lithium environment. The orientational disorder of the quadrupolar cyanide ion in Li 6 PS 5 CN points to a complex interplay of lattice polarizability and molecular dynamics that lower the activation barrier for lithium-ion conductivity in the cyanide argyrodite.

25 ENERGY STORAGE↗
DOE OSTI2022

Delineating the Roles of Mn, Al, and Co by Comparing Three Layered Oxide Cathodes with the Same Nickel Content of 70% for Lithium-Ion Batteries

High-nickel layered oxides continue to prevail in the energy storage market as the frontmost cathode candidates for next-generation lithium-ion batteries. Demand and development of LiNi 1–x–y Mn x Co y O 2 (NMC) and LiNi 1–x–y Co x Al y O 2 (NCA) cathodes are rampantly increasing, particularly for the electric vehicle (EV) industry. However, the continued presence of cobalt in NMC and NCA cathodes raises global concerns due to geopolitical and ethical issues attributed to Co sourcing. We herein introduce a novel cobalt-free, high-nickel cathode LiNi 0.7 Mn 0.25 Al 0.05 O 2 (NMA70) and benchmark it against Co-containing LiNi 0.7 Mn 0.15 Co 0.15 O 2 (NMC70) as well as Co- and Al-free LiNi 0.7 Mn 0.3 O 2 (NM70) cathodes with equivalent 70% Ni contents that are all synthesized in-house. NMA70 displays a high initial C/10 capacity of 210 mA h g –1 , matching that of NMC70 in half cells with a cutoff voltage of 4.5 V. NMA70 also exhibits an impressive high-voltage full cell cycling performance with a cutoff voltage of 4.4 V with a nearly identical capacity retention of 83% compared to that of 82% for NMC70 after 300 cycles. Postmortem X-ray photoelectron spectroscopy (XPS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and electron energy loss spectroscopy (EELS) analyses indicate a thinner cathode–electrolyte interface (CEI) developed in NMA70 compared to that in NM70 and unveil a more robust solid-electrolyte interface (SEI) passivation on the graphite anode among all samples. The benefits of Al doping are additionally highlighted with enhanced high-voltage CEI and thermal stabilities in NMA70. Furthermore, this work assesses the roles of Mn, Al, and Co to demonstrate both the practicality and feasibility of synthesizing cobalt-free, high-nickel cathodes that are promising alternatives to current NMC- and NCA-based cathodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Tuning Magnetic Symmetry and Properties in the Olivine Series Li 1–x Fe x Mn 1–x PO 4 through Selective Delithiation

In this work, we present the first in-depth study of the nuclear and magnetic structures of the fully lithiated LiFe x Mn 1–x PO 4 solid solutions as well as the partially delithiated Li 1– xFe x Mn 1–x PO 4 series using neutron powder diffraction. By using a weak oxidizing solution that only oxidizes Fe 2+ , we find that lithium can be removed from these olivines in a stepwise manner. Representational analysis was performed on the observed magnetic reflections and found that the lithiated solid solutions order in the magnetic space group Pnma', which is identical to triphylite (LiFePO 4 ). We report that, even when removing 20% of the lithium from the hcp lattice, the magnetic structure changes and multiple magnetic contributions are needed to fully encompass the observed magnetic order. We find that the partially delithiated x = 0.2 and 0.3 have a magnetic structure P2 1 '/n11, and when x surpasses 0.3, the magnetic structure changes to P2 1 2 1 2 1 . We give a detailed report on the effect of delithiation on magnetic order, bond distances/angles, and the super- and supersuperexchange interactions in the material. The symmetries of the magnetic order of these solid solutions are then discussed with regard to their potential as ferrotoroidic candidates.

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

Toward Ideal Metal–Organic Framework Thin-Film Growth via Automated Layer-by-Layer Deposition: Examples Based on Perylene Diimide Linkers

Photoactive metal-organic framework (MOF) thin films offer an opportunity for translating the advantages of periodic, crystalline, and tailorable light-harvesting materials directly into devices such as those for photoelectrochemical solar energy conversion. In this study, we report the fabrication of light-absorbing perylene-diimide-containing pillared-paddlewheel MOF thin films using an automated layer-by-layer (LbL) deposition technique. Our focus here is on optimizing the growth of representative chromophoric MOFs as oriented films of uniform and predefined thickness. Growth was examined as a function of metal identity, pillaring ligand composition, and supporting-surface chemical functionality. Further, application of atomic force microscopy (AFM) and complementary techniques revealed that the surface-supported MOFs initially display island-type film growth (Volmer-Weber growth), resulting in comparatively rough films. Further growth is accompanied by the merging of islands, resulting in films that, depending on experimental details, can be remarkably smooth (i.e., roughness on the order of ±1 nm (one structural repeat unit in the pillaring direction)). These details include the use of 1,4-diazabicyclo[2.2.2]octane (DABCO) as a MOF pillar and ALD-grown zinc oxide as a film support (ALD = atomic layer deposition). Also helpful for mitigating island-type growth, at least in part, is the replacement of Zn 2+ by Cu 2+ as the metal component of the MOF. Notably, each of these adjustments entails replacing weaker chemical bonds with stronger ones.

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

Probing of the Noninnocent Role of P in Transition-Metal Phosphide Hydrogen Evolution Reaction Electrocatalysts via Replacement with Electropositive Si

Transition-metal phosphides (TMP) have been identified as promising electrocatalysts for the hydrogen evolution reaction (HER). Despite recent computational investigations identifying P sites as being crucial for hydrogen adsorption, the main mode of optimization for TMPs has been focused on changing the metal sites. Here, to experimentally verify computational hypotheses and provide a route for HER electrocatalyst optimization via ternary compounds, we performed systematic experimental studies of structurally related NiSi 1–x P x phases, namely, Ni 2 SiP, Ni 5 Si 2 P 3 , Ni 3 SiP 2 , and Ni 7 Si 2 P 5 , which are ordered derivatives of the NiSi structure (Pnma, oP-8, MnP structure type). We found that P played a significant role in modulating HER activity in an acidic electrolyte because the incorporation of P in NiSi reduced the overpotential at current density j = 10 mA/cm 2 from η 10 = 529 mV (NiSi) to η 10 = 97 mV (Ni 2 SiP). Ni 2 SiP outperformed the current state-of-the-art Ni5P4 electrocatalyst prepared and studied in identical conditions both in terms of activity and stability, which is attributed to the presence of covalent Ni–Si bonding in the structure. Within the family of ternary Ni–Si–P compounds, electrocatalytic activity correlates with the number of Ni-3d states at the Fermi energy.

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

Toggling Stereochemical Activity through Interstitial Positioning of Cations between 2D V 2 O 5 Double Layers

The 5/6s 2 lone-pair electrons of p-block cations in their lower oxidation states are a versatile electronic and geometric structure motif that can underpin lattice anharmonicity and often engender electronic and structural instabilities that underpin the function of active elements in nonlinear optics, thermochromics, thermoelectrics, neuromorphic computing, and photocatalysis. In contrast to periodic solids where lone-pair-bearing cations are part of the structural framework, installing lone-pair-bearing cations in the interstitial sites of intercalation hosts provides a means of a systematically modulating electronic structure through the choice of the group and the period of the inserted cation while preserving the overall framework connectivity. The extent of stereochemical activity and the energy positioning of lone-pair-derived mid-gap states depend on the cation identity, stoichiometry, and strength of anion hybridization. V 2 O 5 polymorphs are versatile insertion hosts that can accommodate a broad range of s-, p-, and d-block cations. However, the insertion of lone-pair-bearing cations remains largely underexplored. In this article, we examine the implications of varying the 6s 2 cations situated in interlayer sites between condensed [V 4 O 10 ] n double layers. Systematic modulations of lattice distortions, electronic structure, and magnetic ordering are observed with increasing strength of stereochemical activity from group 12 to group 14 cations. We compare and contrast p-block-layered M x V 2 O 5 (M = Hg, Tl, and Pb) compounds and map the significance of local off-centering arising from the stereochemical activity of lone-pair cations to the emergence of filled antibonding lone-pair 6s 2 –O 2p-hybridized mid-gap states mediated by second-order Jahn–Teller distortions. Crystallographic studies of cation coordination environments and the resulting modulation of V–V interactions have been used in conjunction with variable-energy hard X-ray photoelectron spectroscopy measurements, first-principles electronic structure calculations, and crystal orbital Hamilton population analyses to decipher the origins of stereochemical activity. Magnetic susceptibility measurements reveal antiferromagnetic signatures for all the three compounds. However, the differences in V–V interactions significantly affect the energy balance of the superexchange interactions, resulting in an ordering temperature of 160 and 260 K for Hg 0.5 V 2 O 5 and δ-Tl 0.5 V 2 O 5 , respectively, as compared to 7 K for δ-Pb 0.5 V 2 O 5 . In δ-Pb 0.5 V 2 O 5 , the strong stereochemical activity of electron lone pairs and the resulting electrostatic repulsions enforce superlattice ordering, which strongly modifies the electronic localization patterns along the [V 4 O 10 ] slabs, resulting in disrupted magnetic ordering and an anomalously low ordering temperature. The results demonstrate a versatile strategy for toggling the stereochemical activity of electron lone pairs to modify the electronic structure near the Fermi level and to mediate superexchange interactions.

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

Competing Intermolecular and Molecule–Surface Interactions: Dipole–Dipole-Driven Patterns in Mixed Carborane Self-Assembled Monolayers

Carboranedithiol isomers adsorbing with opposite orientations of their dipoles on surfaces are self-assembled together to form mixed monolayers where both lateral dipole–dipole and lateral thiol–thiolate (S–H···S) interactions provide enhanced stability over single-component monolayers. Here, we demonstrate the first instance of the ability to map individual isomers in a mixed monolayer using the model system carboranedithiols on Au{111}. The addition of methyl groups to one isomer provides both an enhanced dipole moment and extra apparent height for differentiation via scanning tunneling microscopy (STM). Associated computational investigations rationalize favorable interactions of mixed pairs and the associated stability changes that arise from these interactions. Both STM images and Monte Carlo simulations yield similarly structured mixed monolayers, where approximately 10% of the molecules have reversed dipole moment orientations but no direct chemical attachment to the surface, leading to homogeneous monolayers with no apparent phase separation. Deprotonating the thiols by depositing the molecules under basic conditions eliminates the lateral S–H···S interactions while accentuating the dipole–dipole forces. The molecular system investigated is composed of isomeric molecules with opposite orientations of dipoles and identical surface packing, which enables the mapping of individual molecules within the mixed monolayers and enables analyses of the contributions of the relatively weak lateral interactions to the overall stability of the assemblies.

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

Effect of H + Exchange and Surface Impurities on Bulk and Interfacial Electrochemistry of Garnet Solid Electrolytes

Contact loss and current constriction pose significant challenges at the Li metal interface of solid-state batteries. For garnet-structured Li 7 La 3 Zr 2 O 12 (LLZO), these effects are amplified by Li + /H + exchange and surface contamination reactions, which lead to conductivity losses and poor Li wetting. In this study, we utilize a variety of surface treatment processes across 37 cells to selectively induce proton exchange and contamination reactions in LLZO. The resulting bulk and surface chemistry is systematically characterized and correlated to changes in electrochemical properties. Additionally, we combine impedance analysis and finite element method modeling to deconvolute sources of impedance contributions at the Li metal interface. Specifically, we show that constriction impedance at the Li metal interface arises not solely from voids, but also from ionically-resistive surface contaminants. Further, these findings emphasize the connection between ionic conductivity and constriction, demonstrating that micron-scale ionically-resistive components increase constriction even with identical contact geometries. Finally, we leverage our comprehensive dataset to highlight unstable overpotential growth as a failure mechanism, additionally showing that the phase of a cell’s impedance is a sensitive indicator for the onset of interfacial instability. Overall, this study clarifies the impacts of proton exchange and surface contamination on electrochemical properties at the Li|solid electrolyte interface and elucidates insights that are generalizable to other solid-state battery systems.

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

Site Disorder Drives Cyanide Dynamics and Fast Ion Transport in Li 6 PS 5 CN

Halide argyrodite solid-state electrolytes of the general formula Li 6 PS 5 X exhibit complex static and dynamic disorder that plays a crucial role in ion transport processes. Here, we unravel the rich interplay between site disorder and dynamics in the plastic crystal argyrodite Li 6 PS 5 CN and the impact on ion diffusion processes through a suite of experimental and computational methodologies, including temperature-dependent synchrotron powder X-ray diffraction, AC electrochemical impedance spectroscopy, 7 Li solid-state NMR, and machine learning-assisted molecular dynamics simulations. Sulfide and (pseudo)halide site disorder between the two anion sublattices unilaterally improves long-range lithium diffusion irrespective of the (pseudo)halide identity, which demonstrates the importance of site disorder in dictating bulk ionic conductivity in the argyrodite family. Furthermore, we find that anion site disorder modulates the presence and time scales of cyanide rotational dynamics. Ordered configurations of anions enable fast, quasi-free rotations of cyanides that occur on time scales of 10 11 Hz at T = 300 K. In contrast, we find that cyanide dynamics are slow or frozen in Li 6 PS 5 CN when site disorder between the cyanide and sulfide sublattices is present at T = 300 K. We rationalize the observed differences in cyanide dynamics in the context of elastic dipole interactions between neighboring cyanide anions and local strain induced by the configurations of site disorder that may impact the energetic landscape for cyanide rotational dynamics. Through this study, we find that anion disorder plays a decisive role in dictating the extent and time scales of both lithium ion and cyanide dynamics in Li 6 PS 5 CN.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Smaller Is Better: The Case for Lower-Order Iodoplumbate Species Dominating MAPbI 3 /Dimethylformamide Solutions

Here, using complementary experimental measurements and computational predictions of spectroscopic measurements (EXAFS, XANES, and UV–vis), we have determined the identity of the most stable iodoplumbate species in dilute lead halide perovskite precursor solutions. We have determined which species are most likely to be thermodynamically stable compared to others that are unstable or metastable. Condensed phase ab initio models were constructed, and the resulting ensembles were used to directly compare the computed signals to the experimental results of the EXAFS, XANES, and UV–vis spectra of PbI 2 :MAI in DMF. The results of this study suggest that only Pb 2+ , PbI + , and PbI 2 are dominant in the dilute lead perovskite precursor solutions as thermodynamically stable entities. Our interpretation of the relative stability of iodoplumbate species in solution, based on an analysis of EXAFS and XANES spectra, provides critically important new insight into the species most likely to be responsible for crystal nucleation and growth in these materials. This insight will have a significant consequence on the broad scientific community and will necessitate the reinterpretation of peaks in the UV–vis spectra of lead halide perovskite precursor solutions.

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

Role of Short-Range Order on Diffusion Coefficients in the Li–Mg Alloy

Li–Mg alloys are important because of their beneficial role in fostering uniform plating and stripping of lithium in all-solid-state batteries. The alloy Li x Mg 1–x forms a solid solution on the BCC crystal structure when the lithium content is greater than x ≈ 0.3. The activation barriers of lithium and magnesium exchanges with a vacancy, crucial for substitutional diffusion, are predicted to be exceptionally low and almost identical, with negligible dependence on the alloy composition. The equilibrium vacancy concentration at room temperature is predicted to be very low, and it also remains almost constant with no dependence on Mg content in the alloy (for x Li ≥ 0.5). Nevertheless, both experiments and kinetic Monte Carlo simulations indicate that the tracer diffusion coefficients decrease by almost an order of magnitude with the addition of Mg to the alloy. In this contribution, the crucial role that chemical short-range order plays in affecting the diffusion coefficients is studied. Chemical short-range order is found to increase the effective activation barrier for lithium and magnesium diffusion by making successive atomic hops with vacancies correlated.

36 MATERIALS SCIENCE↗