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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Dy4CdSe7 by Materials Project

Dy4CdSe7 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are four inequivalent Dy3+ sites. In the first Dy3+ site, Dy3+ is bonded to seven Se2- atoms to form distorted DySe7 pentagonal bipyramids that share corners with four DySe6 octahedra, corners with four equivalent CdSe6 octahedra, an edgeedge with one CdSe6 octahedra, edges with three equivalent DySe6 octahedra, edges with two equivalent DySe7 pentagonal bipyramids, and faces with two equivalent DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 22–70°. There are a spread of Dy–Se bond distances ranging from 2.85–3.19 Å. In the second Dy3+ site, Dy3+ is bonded to seven Se2- atoms to form distorted DySe7 pentagonal bipyramids that share corners with two equivalent CdSe6 octahedra, corners with six DySe6 octahedra, edges with four DySe6 octahedra, edges with two equivalent DySe7 pentagonal bipyramids, and faces with two equivalent DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 22–68°. There are a spread of Dy–Se bond distances ranging from 2.84–3.13 Å. In the third Dy3+ site, Dy3+ is bonded to six Se2- atoms to form DySe6 octahedra that share a cornercorner with one DySe6 octahedra, a cornercorner with one CdSe6 octahedra, corners with four DySe7 pentagonal bipyramids, edges with two equivalent DySe6 octahedra, and edges with six DySe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 54–55°. There are a spread of Dy–Se bond distances ranging from 2.80–2.88 Å. In the fourth Dy3+ site, Dy3+ is bonded to six Se2- atoms to form DySe6 octahedra that share a cornercorner with one DySe6 octahedra, corners with two equivalent CdSe6 octahedra, corners with six DySe7 pentagonal bipyramids, edges with two equivalent DySe6 octahedra, edges with three equivalent CdSe6 octahedra, and an edgeedge with one DySe7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–54°. There are a spread of Dy–Se bond distances ranging from 2.78–2.92 Å. Cd2+ is bonded to six Se2- atoms to form CdSe6 octahedra that share corners with three DySe6 octahedra, corners with six DySe7 pentagonal bipyramids, edges with two equivalent CdSe6 octahedra, edges with three equivalent DySe6 octahedra, and an edgeedge with one DySe7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–55°. There are a spread of Cd–Se bond distances ranging from 2.77–2.90 Å. There are seven inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to four Dy3+ and one Cd2+ atom to form distorted SeDy4Cd trigonal bipyramids that share corners with five SeDy3Cd tetrahedra, corners with four SeDy5 trigonal bipyramids, an edgeedge with one SeDy4 tetrahedra, and edges with five SeDy4Cd trigonal bipyramids. In the second Se2- site, Se2- is bonded to three Dy3+ and two equivalent Cd2+ atoms to form distorted SeDy3Cd2 trigonal bipyramids that share corners with five SeDy3Cd tetrahedra, corners with four SeDy5 trigonal bipyramids, an edgeedge with one SeDy3Cd tetrahedra, and edges with five SeDy4Cd trigonal bipyramids. In the third Se2- site, Se2- is bonded to five Dy3+ atoms to form distorted SeDy5 trigonal bipyramids that share corners with four equivalent SeDy3Cd tetrahedra, corners with six SeDy4Cd trigonal bipyramids, edges with three SeDy3Cd tetrahedra, and edges with six SeDy3Cd2 trigonal bipyramids. In the fourth Se2- site, Se2- is bonded to five Dy3+ atoms to form distorted SeDy5 trigonal bipyramids that share corners with four equivalent SeDy4 tetrahedra, corners with six SeDy4Cd trigonal bipyramids, edges with three SeDy3Cd tetrahedra, and edges with six SeDy4Cd trigonal bipyramids. In the fifth Se2- site, Se2- is bonded to three Dy3+ and one Cd2+ atom to form distorted SeDy3Cd tetrahedra that share corners with three SeDy3Cd tetrahedra, corners with nine SeDy4Cd trigonal bipyramids, and edges with four SeDy3Cd2 trigonal bipyramids. In the sixth Se2- site, Se2- is bonded to four Dy3+ atoms to form distorted SeDy4 tetrahedra that share corners with three SeDy3Cd tetrahedra, corners with nine SeDy4Cd trigonal bipyramids, and edges with four SeDy4Cd trigonal bipyramids. In the seventh Se2- site, Se2- is bonded in a square co-planar geometry to two equivalent Dy3+ and two equivalent Cd2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(GaSe2)2 by Materials Project

EuGa2Se4 crystallizes in the orthorhombic Fddd space group. The structure is three-dimensional. there are three inequivalent Eu2+ sites. In the first Eu2+ site, Eu2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Eu–Se bond distances ranging from 3.23–3.28 Å. In the second Eu2+ site, Eu2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are four shorter (3.23 Å) and four longer (3.25 Å) Eu–Se bond lengths. In the third Eu2+ site, Eu2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are four shorter (3.22 Å) and four longer (3.27 Å) Eu–Se bond lengths. There are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to four Se2- atoms to form a mixture of corner and edge-sharing GaSe4 tetrahedra. There are a spread of Ga–Se bond distances ranging from 2.41–2.46 Å. In the second Ga3+ site, Ga3+ is bonded to four Se2- atoms to form a mixture of corner and edge-sharing GaSe4 tetrahedra. There are a spread of Ga–Se bond distances ranging from 2.42–2.46 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to two Eu2+ and two Ga3+ atoms. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to two Eu2+ and two Ga3+ atoms. In the third Se2- site, Se2- is bonded in a 4-coordinate geometry to two Eu2+ and two equivalent Ga3+ atoms. In the fourth Se2- site, Se2- is bonded in a 4-coordinate geometry to two Eu2+ and two equivalent Ga3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba5(GaSe4)2 by Materials Project

Ba5Ga2Se8 crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are three inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Ba–Se bond distances ranging from 3.15–3.81 Å. In the second Ba2+ site, Ba2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Ba–Se bond distances ranging from 3.24–3.75 Å. In the third Ba2+ site, Ba2+ is bonded in a distorted q6 geometry to ten Se2- atoms. There are a spread of Ba–Se bond distances ranging from 3.63–3.77 Å. There are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded in a tetrahedral geometry to four Se2- atoms. There are a spread of Ga–Se bond distances ranging from 2.40–2.53 Å. In the second Ga3+ site, Ga3+ is bonded in a tetrahedral geometry to four Se2- atoms. There are two shorter (2.42 Å) and two longer (2.43 Å) Ga–Se bond lengths. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to five Ba2+ and one Ga3+ atom. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to five Ba2+ and one Ga3+ atom. In the third Se2- site, Se2- is bonded in a 1-coordinate geometry to six Ba2+ and one Ga3+ atom. In the fourth Se2- site, Se2- is bonded in a 1-coordinate geometry to six Ba2+ and one Ga3+ atom. In the fifth Se2- site, Se2- is bonded in a 6-coordinate geometry to five Ba2+ and one Ga3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Visualizing Tailored Spin Phenomena in a Reduced‐Dimensional Topological Superlattice

Abstract Emergent topological insulators (TIs) and their design are in high demand for manipulating and transmitting spin information toward ultralow‐power‐consumption spintronic applications. Here, distinct topological states with tailored spin properties can be achieved in a single reduced‐dimensional TI‐superlattice, (Bi 2 /Bi 2 Se 3 )‐(Bi 2 /Bi 2 Se 3 ) N or (□/Bi 2 Se 3 )‐(Bi 2 /Bi 2 Se 3 ) N ( N is the repeating unit, □ represents an empty layer) by controlling the termination via molecular beam epitaxy. The Bi 2 ‐terminated superlattice exhibits a single Dirac cone with a spin momentum splitting ≈0.5 Å −1 , producing a pronounced inverse Edelstein effect with a coherence length up to 1.26 nm. In contrast, the Bi 2 Se 3 ‐terminated superlattice is identified as a dual TI protected by coexisting time reversal and mirror symmetries, showing an unexpectedly long spin lifetime up to 1 ns. The work elucidates the key role of dimensionality and dual topological phases in selecting desired spin properties, suggesting a promise route for engineering topological superlattices for high‐performance TI‐spintronic devices.

Sun, Rui↗
DOE OSTI2023

Synthesis of Pyrimidine Modified Seleno–DNA as a Novel Approach to Antisense Candidate

Chemically modified antisense oligonucleotides (ASO) currently in pre–clinical and clinical experiments mainly focus on the 2’–position derivatizations to enhance stability and targeting affinity. Considering the possible incompatibility of 2’–modifications with RNase H stimulation and activity, we have hypothesized that the atom specific modifications on nucleobases can retain the complex structure and RNase H activity, while enhancing ASO's binding affinity, specificity, and stability against nucleases. Herein we report a novel strategy to explore our hypothesis by synthesizing the deoxynucleoside phosphoramidite building block with the seleno–modification at 5–position of thymidine, as well as its Se–oligonucleotides. Via X–ray crystal structural study, we found that the Se–modification was located in the major groove of nucleic acid duplex and didn't cause the thermal and structural perturbations. Surprisingly, our nucleobase–modified Se–DNAs were exceptionally resistant to nuclease digestion, while compatible with RNase H activity. In conclusion, this affords a novel avenue for potential anti–sense modification in the form of Se–antisense oligonucleotides (Se–ASO).

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

Contrasting roles of rice root iron plaque in retention and plant uptake of silicon, phosphorus, arsenic, and selenium in diverse paddy soils

Abstract Background and aims Iron (Fe) plaque on rice roots is a mixture of Fe oxide and oxyhydroxide minerals thought to protect rice from high levels of arsenic (As) in flooded paddy soils. Silicon (Si), phosphorus (P), and selenium (Se) also exist as oxyanions in rice paddies, but the impacts of Fe plaque on uptake of these nutrients are unknown. Methods We used natural variation in paddy soil chemistry to test how Si, P, As, and Se move from porewater to plaque to plant via multiple techniques. In a pot study, we monitored Fe plaque deposition and porewater chemistry in 5 different soils over time and measured plaque/plant chemistry and Fe plaque mineralogy at harvest. We normalized oxyanion concentrations by Fe to determine the preferential retention on plaque or plant uptake. Results Low phosphorus availability increased root Fe-oxidizing activity, while Fe, Si, P, As, and Se concentrations in plaque were strongly correlated with porewater. Plaque did not appreciably retain Si and Se, and the oxyanions did not compete for adsorption sites on the Fe plaque. Conclusion Root Fe plaque seems to protect rice from As uptake, does not interfere with Si and Se uptake, and roots adapt to maintain P nutrition even with retention of porewater P on plaque.

Agriculture↗
DOE OSTI2024

Chalcogen effect on the photovoltaic performance of nonfused-ring small molecular electron acceptors for efficient organic solar cells

Fused-ring electron acceptors (FREAs) are the current working horse for the top performing organic solar cells (OSCs). Nevertheless, these FREAs surfer from high synthetic complexity, production costs and poor scalability, hindering their industrialization. Developing nonfused-ring electron acceptors (NFREAs) is a more feasible alternative solution towards future photovoltaic applications. Here, in this work, a series of NFREAs have been designed and synthesized by introducing chalcogen atoms on the side chains for OSCs. The introduced chalcogen atoms (O, S, and Se) not only modulated the energy levels but also finely tuned the intermolecular interactions. Especially, the formed S···S and Se···Se intermolecular interactions in TTS-4F and TTSe-4F resulted in higher molecular crystallinity than TTO-4F. Unexpectedly, the strong Se···Se interactions also led the aggregation of TTSe-4F and formation of large domains in the PM6:TTSe-4F blend. The moderate S···S interactions in TTS-4F enabled an optimal phase separation with more ideal nano fibrils distributed in the PM6:TTS-4F blend, facilitating the charge separation and transport. As a result, TTS-4F based devices achieved a champion power conversion efficiency (PCE) of 14.74%, higher than the TTO-4F (8.76%) and TTSe-4F (11.56%) based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Regulated lithium ionic flux through well-aligned channels for lithium dendrite inhibition in solid-state batteries

The utilization of solid electrolyte (SE) to suppress lithium (Li) dendrites is promising but still far from satisfactory due to the inhomogeneous Li plating/stripping. In this paper, we demonstrated a novel strategy to inhibit Li dendrites via regulating Li-ion flux in SE by using vertically aligned channels. The ion-insulating walls facilitated uniform distribution of Li-ion flux through the channels, leading to a homogeneous Li deposition, thus alleviating Li dendrite formation. As a result, symmetric cells with this SE exhibited excellent long-term stability (1000 h) against Li metal. In addition, Li4Ti5O12 (LTO)/Li cell with the developed SE achieved good battery performance over 100 cycles. The mechanism for dendrite suppression was further investigated by phase-field simulation. This work provides a novel strategy by manipulating uniform Li-ion flux to fabricate SE to inhibit Li dendrites and facilitates the development of high-performance rechargeable Li batteries.

25 ENERGY STORAGE↗
DOE OSTI2023

The CeBrA demonstrator for particle-γ coincidence experiments at the FSU Super-Enge Split-Pole Spectrograph

We report on a highly selective experimental setup for particle-γ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr scintillators for γ-ray detection. Specifically, we report on the results of characterization tests for the first five CeBr 3 scintillation detectors of the CeBr 3 Array (CeBrA) with respect to energy resolution and timing characteristics. We also present results from the first particle-γ coincidence experiments successfully performed with the CeBrA demonstrator and the FSU SE-SPS. We show that with the new setup, γ-decay branching ratios and particle-γ angular correlations can be measured very selectively using narrow excitation energy gates, which are possible thanks to the excellent particle energy resolution of the SE-SPS. In addition, we highlight that nuclear level lifetimes in the nanoseconds regime can be determined by measuring the time difference between particle detection with the SE-SPS focal-plane scintillator and γ-ray detection with the fast CeBrA detectors. As a result, selective excitation energy gates with the SE-SPS exclude any feeding contributions to these lifetimes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Unleashing the Potential of Fast Charging Batteries: Leveraging Anion Redox Chemistry in Ni- and Co-Free Cathodes

Designing Li-ion battery cathodes free from critical raw materials such as Co and Ni has a huge technological and societal impact. Though anion redox-based Li-rich oxide cathodes allow designing Co and Ni free cathode compositions, the Li-rich oxides witnessed voltage fade, voltage hysteresis, and irreversible oxygen release despite their high capacity. Conversely, anion redox through highly covalent chalcogenides (S/Se) is emerging due to the improved covalency between metal d and ligand p bands. Here, we investigate the tuning of multi-chalcogen (S/Se) p-band and redox-active metal d-band in a model Li-rich chalcogen composition Li 1.13 Ti 0.57 Fe 0.3 S 2-y Se y (y = 0 - 1) through in-depth electrochemical, X-ray spectroscopy, and DFT-based electronic structure investigations. Introducing the appropriate amount of Se p band character in anion redox sulfides increases interlayer distance and metal - ligand covalency without modifying the original crystal structure, promoting significant electrochemical reversibility through mixed anionic (Se 2- /Se n- , S 2- /S n- , wherein n<2) and cationic (Fe 2+ /Fe 3+ ) redox reactions. Here we show the detailed Fe, S, and Se redox contributions during Li insertion/extraction through X-ray Absorption (XAS) and Hard X-ray Photoemission Spectroscopy (HAXPES) measurements. The orbital tuning approach improves rate capability for more than 10 C charge-discharge rate, exhibiting more than 50% of its original capacity obtained at C/20 rate. The buffer cation in the lattice (Ti 4+ ) remains electrochemically inactive even after significant Se p-band introduction in the sulfide framework. Overall, this work takes advantage of multi-anion redox chemistry to uncover practically demanding fast charging-discharging characteristics in intercalation cathodes. The obtained knowledge of this design can be extended to other oxide and chalcogen cathodes for high performance Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Strong Correlation Between Superconductivity and Ferromagnetism in an Fe-Chalcogenide Superconductor

The interplay among topology, superconductivity, and magnetism promises to bring a plethora of exotic and unintuitive behaviors in emergent quantum materials. The family of Fe-chalcogenide superconductors FeTe x Se 1–x are directly relevant in this context due to their intrinsic topological band structure, high-temperature superconductivity, and unconventional pairing symmetry. Despite enormous promise and expectation, the local magnetic properties of FeTe x Se 1–x remain largely unexplored, which prevents a comprehensive understanding of their underlying material properties. Exploiting nitrogen vacancy (NV) centers in diamond, here we report nanoscale quantum sensing and imaging of magnetic flux generated by exfoliated FeTe x Se 1–x flakes, demonstrating strong correlation between superconductivity and ferromagnetism in FeTe x Se 1–x . The coexistence of superconductivity and ferromagnetism in an established topological superconductor opens up new opportunities for exploring exotic spin and charge transport phenomena in quantum materials. The demonstrated coupling between NV centers and FeTe x Se 1–x may also find applications in developing hybrid architectures for next-generation, solid-state-based quantum information technologies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Size-Dependent Chemomechanical Failure of Sulfide Solid Electrolyte Particles during Electrochemical Reaction with Lithium

The very high ionic conductivity of Li 10 GeP 2 S 12 (LGPS) solid electrolyte (SE) makes it a promising candidate SE for solid-state batteries in electrical vehicles. However, chemomechanical failure, whose mechanism remains unclear, has plagued its widespread applications. Here, we report in situ imaging lithiation-induced failure of LGPS SE. In this work, we revealed a strong size effect in the chemomechanical failure of LGPS particles: namely, when the particle size is greater than 3 μm, fracture/pulverization occurred; when the particle size is between 1 and 3 μm, microcracks emerged; when the particle size is less than 1 μm, no chemomechanical failure was observed. This strong size effect is interpreted by the interplay between elastic energy storage and dissipation. Our finding has important implications for the design of high-performance LGPS SE, for example, by reducing the particle size to less than 1 μm the chemomechanical failure of LGPS SE can be mitigated.

25 ENERGY STORAGE↗
DOE OSTI2025

Alkaline Earth-Based Ternary Chalcogenide Nanocrystals: Cadmium- and Lead-Free Optical Materials

As some of the most abundant elements on the Earth’s crust, alkaline earths bear great potential in Cd- and Pb-free catalytic, energy conversion, and light-emitting devices. Further, because large electropositive alkaline earths (Ae) can adopt high coordination numbers, they offer structural complexity beyond the tetrahedral (c-Si, II–VI, III–V) or octahedral (IV–VI) atomic sites that─with the notable exception of halide perovskites─are ubiquitous among nanocrystalline semiconductors. Here, in this work, we present a general route to photoluminescent 6–125 nm nanocrystals of ternary AeIn 2 Ch 4 semiconductors (Ae = Sr, Ba; Ch = S, Se) featuring eight- (Ae) as well as four-coordinate (In and Ch) atomic sites. Powder X-ray diffraction, electron microscopy, optical absorption, photoluminescence, and solid-state (ss)NMR spectroscopies attest to the ternary composition and phase purity of the nanocrystals. Continuous shape measures pinpoint the degree of distortion of individual crystallographic sites from ideal coordination polyhedra, allowing us to identify two very distinct types of Se coordination environments. Based on their higher order, pseudo-3-fold rotational symmetry, we assign 77 Se ssNMR peaks with negligible chemical shift anisotropy (CSA) to pyramidalized Se sites with vacant-trigonal bipyramid-like geometries and those with larger CSA to lower symmetry Se sites with seesaw-distorted geometries. Calculations help to better understand the electronic band structure of these materials. The nanocrystals are stable at room temperature in open air for several weeks, and some compositions up to 1000 °C under Ar, making them strong candidates for practical applications.

alkaline earth↗
DOE OSTI2023

Near Quantitative Removal of Selenate and Sulfate Anions from Wastewaters by Cocrystallization with Chelating Hydrogen-Bonding Guanidinium Ligands

Selenium (Se) has become an environmental contaminant of aquatic ecosystems as a result of human activities, particularly mining, fossil fuel combustion, and agricultural activities. By leveraging the high sulfate concentrations relative to Se oxyanions (i.e., SeO n 2– , n = 3, 4) present in some wastewaters, we have developed an efficient approach to Se-oxyanion removal by cocrystallization with bisiminoguanidinium (BIG) ligands that form crystalline sulfate/selenate solid solutions. The crystallization of the sulfate, selenate and selenite, oxyanions and of sulfate/selenate mixtures with five candidate BIG ligands are reported along with the thermodynamics of crystallization and aqueous solubilities. Oxyanion removal experiments with the top two performing candidate ligands show a near quantitative removal (>99%) of sulfate or selenate from solution. When both sulfate and selenate are present, there is near quantitative removal (>99%) of selenate, down to sub-ppb Se levels, with no discrimination between the two oxyanions during cocrystallization. Reducing the selenate concentrations by 3 orders of magnitude or more relative to sulfate, as found in many wastewaters, led to no measurable loss in Se removal efficiencies. This work offers a simple and effective alternative to selective separation of trace amounts of highly toxic selenate oxyanions from wastewaters, to meet stringent regulatory discharge limits.

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

Decoupling first-cycle capacity loss mechanisms in sulfide solid-state batteries

Solid-state batteries (SSBs) promise more energy-dense storage than liquid electrolyte lithium-ion batteries (LIBs). However, first-cycle capacity loss is higher in SSBs than in LIBs due to interfacial reactions. The chemical evolution of key interfaces in SSBs has been extensively characterized. Electrochemically, however, we lack a versatile strategy for quantifying the reversibility of solid electrolyte (SE) redox for established and next-generation SSB electrolytes. In this work, we perform tailored electrochemical tests and operando X-ray diffraction to disentangle reversible and irreversible sources of capacity loss in positive electrodes composed of Li 6 PS 5 Cl SE, Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 (NMC), and carbon conductive additives. We leverage an atypically low voltage cutoff (2.0 V vs. Li/Li + ) to quantify the reversibility of SE redox. Using slow (5.5 mA g NMC −1 ) cycling paired with >100 h low-voltage holds, our cells achieve a surprising 96.2% first-cycle coulombic efficiency, which is higher than previously reported (mean: 72%, maximum: 91.6% across surveyed literature). We clarify that sluggish NMC relithiation kinetics have been historically mistaken for permanently irreversible capacity loss. In conclusion, through systematic decoupling of loss mechanisms, we uncover the unexpected reversibility of SE redox and isolate the major contributors to capacity loss, outlining a strategy for accurate assessment of next-generation SE materials and interface modifications.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Comparison of multi-stage air treatment process divided by the same temperature and enthalpy difference

The multi-stage air treatment system has been proposed recently, and lower grade chilled/hot water could be used and energy efficiency could be improved. However, it has not been studied which division method of air treatment processes has higher energy efficiency. In this study, the model to calculate the energy consumption of multi-stage air treatment process is introduced, and the effects of two division methods, i.e. multi-stage air treatment process divided by the same temperature difference (ST method) or same enthalpy difference (SE method) between inlet and outlet at each stage, under 9 different air inlet parameters in the 2-stage and 3-stage air treatment processes are analysed and compared. The results show that (1) the system energy consumption of the SE method is generally lower than that of the ST method; (2) there is generally a larger energy consumption reduction rate of SE method when the air relative humidity is 70% compared to relative humidity of 50% and 90%; (3) the difference between ST method and SE method is not great, so both methods can be used for the design of multi-stage treatment system although SE method is normally recommended.

Wang, Wentao↗
DOE OSTI2022

Epitaxial growth and magnetic characterization of EuSe thin films with various crystalline orientations

Here, we report different growth modes and corresponding magnetic properties of thin EuSe films grown by molecular beam epitaxy on BaF 2 , Pb 1-x Eu x Se, GaAs, and Bi 2 Se 3 substrates. We show that EuSe grows predominantly in the (001) orientation on GaAs(111) and Bi 2 Se 3 , but along the (111) crystallographic direction on BaF 2 (111) and Pb 1-x Eu x Se (111). High resolution transmission electron microscopy measurements reveal a sharp and highly crystalline interface for both (001) and (111) EuSe films. In agreement with previous studies, ordered magnetic phases include antiferromagnetic, ferrimagnetic, and ferromagnetic phases. In contrast to previous studies, we found a strong hysteresis of the antiferromagnetic–ferrimagnetic transition. The ability to grow epitaxial films of EuSe on Bi 2 Se3 and of Bi 2 Se 3 on EuSe enables further investigation of interfacial exchange interactions between various phases of an insulating metamagnetic material and a topological insulator.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Electronic structure, magnetic properties, spin orientation, and doping effect in Mn 3 Si 2 Te 6

The layered material Mn 3 Si 2 Te 6 , with alternating stacking honeycomb and triangular layers, is attracting considerable attention due to its rich physical properties. Here, in this study, using density functional theory and classical Monte Carlo (MC) methods, we systematically study this system with the 3d 5 electronic configuration. Near the Fermi level, the states are mainly contributed by Te 5p orbitals hybridized with Mn 3d orbitals, resembling a charge-transfer system. Furthermore, the spin orientations of the ferrimagnetic (FiM) ground state display different conductive behaviors when along the ab plane or out-of-plane directions: insulating vs metallic states. The energy difference between the FiM [110] insulating and FiM [001] metallic phases is very small (~0.71 meV/Mn) . Changing the angle θ of spin orientation from in-plane to out-of-plane directions, the band gaps of this system are gradually reduced, leading to an insulator-metal transition, resulting in an enhanced electrical conductivity, related to the colossal angular magnetoresistance (MR) effect. Although the three main magnetic couplings were found to be antiferromagnetic, overall the ground state is FiM. In addition, we also constructed the magnetic phase diagram using the classical XY spin model studied with the MC method. Three magnetic phases were obtained, including antiferromagnetic order, noncollinear spin patterns, and FiM order. Moreover, we also investigated the Se and Ge doping into the Mn 3 Si 2 Te 6 system: the FiM state has the lowest energy among the magnetic candidates for both Se- and Ge-doped cases. The magnetic anisotropy energy (MAE) decreases in the Se-doped case because the Mn orbital moment is reduced as the doping x increases. Due to the small spin-orbit-coupling effect of Se, the insulator-metal transition caused by the spin orientation disappears in the Se-doped case, resulting in an insulating phase in the FiM [001] phase. This causes a reduced colossal angular MR. However, both the MAE and the band gap of the Ge-doped case do not change much with increasing doping x . Our results for Mn 3 Si 2 Te 6 could provide guidance to experimentalists and theorists working on this system or related materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗