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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Nonexcitonic mechanism for electronic and structural phase transitions in Ta 2 ⁢Ni⁢(Se,S) 5

Here, we present a first-principles study based on density functional theory (DFT) on the electronic and structural properties of Ta 2 NiSe 5 , a layered transition metal chalcogenide that has been considered as a possible candidate for an excitonic insulator. Our systematic DFT results however provide a nonexcitonic mechanism for the experimentally observed electronic and structural phase transitions in Ta 2 NiSe 5 , in particular explaining why sulfur substitution of selenium reduces the distortion angle in the low-temperature phase and potassium dosing closes the gap in the electronic structure. Moreover, the calculations show that these two effects couple to each other. Further, our first-principles calculations predict several changes in both the crystal structure and electronic structure under the effects of uniform charge dosing and uniaxial strain, which could be tested experimentally.

Tang, Weichen [University of California, Berkeley,↗
DOE OSTI2022

Thermoelectricity and electronic correlation enhancement in FeS by light Se doping

We report thermoelectric studies of FeS 1–x Se x (x = 0, 0.06) superconducting single crystals that feature high irreversibility fields and critical current density J c comparable to materials with much higher superconducting critical temperatures (T c 's). The ratio of T c to the Fermi temperature T F is very small, indicating weak electronic correlations. With a slight selenium substitution on sulfur site in FeS both T c /T F and the effective mass m* rise considerably, implying increase in electronic correlation of the bulk conducting states. The first-principle calculations show rise of the density of states at the Fermi level in FeS 0.94 Se 0.06 when compared to FeS, which is related not only to Fe but also to chalcogen-derived electronic states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Localized excitons in defective monolayer germanium selenide

Germanium selenide (GeSe) is a van der Waals–bonded layered material with promising optoelectronic properties, which has been experimentally synthesized for two-dimensional (2D) semiconductor applications. In the monolayer, due to reduced dimensionality and, thus, screening environment, perturbations such as the presence of defects have a significant impact on its properties. We apply density functional theory and many-body perturbation theory to understand the electronic and optical properties of GeSe containing a single selenium vacancy in the –2 charge state. We predict that the vacancy results in midgap “trap states” that strongly localize the electron and hole density and lead to sharp, low-energy optical absorption peaks below the predicted pristine optical gap. Analysis of the exciton wave function reveals that the 2D Wannier-Mott exciton of the pristine material monolayer is strongly modified by the presence of the defect. The lowest-energy exciton wave function is highly localized around the defect, with the Bohr radius reduced by a factor of 4 when compared to the pristine material and a dipole moment along the out-of-plane axis due to the defect-induced symmetry breaking. Altogether, these results suggest that the vacancy significantly modifies the excitonic properties of the system, demonstrating the importance of considering defects in the context of material design.

2-dimensional systems↗
DOE OSTI2022

Negative linear compressibility in Se at ultra-high pressure above 120 GPa

A series of in situ synchrotron X-ray diffraction (XRD) measurements were carried out, combined with first-principles calculations, to study structural phase transitions of selenium at high pressures and room temperature. Several phase transitions were observed, among which an isostructural phase transition was found at around 120 GPa for the first time. Evolved from the rhombohedral (space group R$\bar{3}$m) structure (Se-V), the new phase (Se-V') exhibited an interesting increase of lattice parameter a at pressures from 120 to 148 GPa, known as negative linear compressibility (NLC). The discovery of NLC behavior observed in this work is mainly attributed to the accuracy and fine steps controlled by the membrane system for in situ XRD data collected with an exposure time of 0.5 s. After 140 GPa, a body-centered cubic (b.c.c.) structure Se-VI (space group Im$\bar{3}$m) was formed, which remains stable up to 210 GPa, the highest pressure achieved in this study. The bulk moduli of phases Se-V, Se-V' and Se-VI were estimated to be 83 ± 2, 321 ± 2 and 266 ± 7 GPa, respectively, according to the P–V curve fit by the third-order Birch–Murnaghan equation of state. The Se-V' phase shows a bulk modulus almost 4 times larger than that of the Se-V phase, which is mainly due to the effect of its NLC. NLC in a higher pressure range is always more significant in terms of fundamental mechanism and new materials discovery, yet it has barely been reported at pressures above 100 GPa. This will hopefully inspire future studies on potential NLC behaviors in other materials at ultra-high pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Growth of Cd 0.9 Zn 0.1 Te 1-y Se y Single Crystals for Room Temperature Gamma-Ray Detection

Quaternary Cd 0.9 Zn 0.1 Te 1-y Sey (CZTS) single crystals, a novel room-temperature nuclear radiation detector semiconductor material, have been grown using a modified vertical Bridgman method (VBM) and a travelling heater method (THM). The percentage concentration of selenium in the VBM-grown crystal was 3% and that in the THM-grown crystal was 2%. While the THM Frisch collar detector (4.4 × 4.4 × 10.7 mm 3 ) produced a highly resolved pulse height spectra (PHS) with a resolution of ~1.06% for 662-keV gamma rays without any correction, the VBM-grown detector (10 × 10 × 2 mm 3 ) offered a high energy resolution of ~2% after application of a digital biparametric correction. The high-resolution performance of these detectors has been attributed to the addition of Se in the Cd 0.9 Zn 0.1 Te (CZT) matrix. Ab-initio calculations based on density functional theory (DFT) also confirmed that the addition of Se in the CZT matrix helps to reduce the formation of TeCd and the TeZn anti-sites. The VBM-grown crystals were characterized using powder x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS). While XRD results revealed sharp diffraction peaks confirming the crystalline nature of the grown crystal, the EDS results confirmed the targeted stoichiometry of the elemental composition. The bulk resistivity of the grown crystal was calculated to be ~3 × 10 10 Ω-cm from current-voltage characteristics recorded at room temperature in a planar configuration, ensuring that the grown CZTS crystals have low dark current as required for detector-grade crystals.

42 ENGINEERING↗
DOE OSTI2021

Self-assembled nanocolumns in Bi 2 Se 3 grown by molecular beam epitaxy

Layered van der Waals (vdW) materials grown by physical vapor deposition techniques are generally assumed to have a weak interaction with the substrate during growth. This leads to films with relatively small domains that are usually triangular and a terraced morphology. In this paper, we demonstrate that Bi 2 Se 3 , a prototypical vdW material, will form a nano-column morphology when grown on GaAs(001) substrates. This morphology is explained by a relatively strong film/substrate interaction, long adatom diffusion lengths, and a high reactive selenium flux. In conclusion, this discovery paves the way toward growth of self-assembled vdW structures even in the absence of strain.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Review of Direct Neutron Conversion and Detection Processes

Commercial and laboratory neutron detection systems use indirect neutron response of materials like pressurized helium-3 (via nuclear reaction 3He(n, p)3H) to measure and count neutrons emanating from a source. Recently a host of semiconductors, especially a ternary semiconductor of lithium indium diselenide (6LiInSe2) and a quaternary alloy of enriched lithium-6, indium, phosphorous, and selenium (6LiInP2Se6), have shown promising neutron counting possibilities by directly converting neutrons into charge-carrying elements within the body of the semiconductor. These semiconductors have high thermal neutron capture cross sections, suitable energy bandgaps (~2.0 electron volts) for room-temperature operations, and a favorable electronic band structure for efficient electron charge transport. The article examines the semiconductor properties of these compounds in terms of their neutron counting capabilities and possible ways to extract neutron energy information from them. Lithium-6 and boron-10 (with thermal neutron absorption cross sections of 938 ± 6 and 3855 ± 26 barns, respectively) produce charged particles to be measured via indirect neutron interactions. The efficiency of indirect conversion neutron detectors is limited because of the inefficiencies in conversion mechanism. In case of direct conversion, the neutrons create charged particles in a single material for neutron capture and charge collection, increasing detection efficiency. Unlike 3He proportional counters, which provide no neutron energy information, the semiconductors can be used as neutron energy spectrometer. Fully resolved neutron energy by 6LiInP2Se6 from a plutonium-beryllium source has been reported in the literature. We will discuss the influence of these multilayered semiconductors’ crystallographic structures and growth techniques on neutron energy determination.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2020

Covalent surface modifications and superconductivity of two-dimensional metal carbide MXenes

Versatile chemical transformations of surface functional groups in two-dimensional transition-metal carbides (MXenes) open up a previously unexplored design space for this broad class of functional materials. We introduce a general strategy to install and remove surface groups by performing substitution and elimination reactions in molten inorganic salts. Successful synthesis of MXenes with oxygen, imido, sulfur, chlorine, selenium, bromine, and tellurium surface terminations, as well as bare MXenes (no surface termination), was demonstrated. These MXenes show distinctive structural and electronic properties. For example, the surface groups control interatomic distances in the MXene lattice, and Ti n +1 C n ( n = 1, 2) MXenes terminated with telluride (Te 2− ) ligands show a giant (>18%) in-plane lattice expansion compared with the unstrained titanium carbide lattice. The surface groups also control superconductivity of niobium carbide MXenes.

Kamysbayev, Vladislav↗
DOE OSTI2022

Accelerator commissioning and rare isotope identification at the Facility for Rare Isotope Beams

In 2008, Michigan State University was selected to establish the Facility for Rare Isotope Beams (FRIB). Construction of the FRIB accelerator was completed in January 2022. Phased accelerator commissioning with heavy ion beams started in 2017 with the normal-conducting ion source and radio-frequency quadrupole. In April 2021, the full FRIB driver linear accelerator (linac) was commissioned, with heavy ion beams accelerated to energies above 200 MeV/nucleon by 324 superconducting radiofrequency (SRF) resonators operating at 2 K and 4 K with liquid-helium cooling. Further, in preparation for high-power operation, a liquid lithium charge stripper was commissioned with heavy ion beams up to uranium-238, followed by the simultaneous acceleration of multiple-charge-state heavy ion beams to energies above 200 MeV/nucleon. In December 2021, selenium-84 was produced with the FRIB target using a krypton-86 primary beam, demonstrating FRIB’s capability for scientific discovery.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Hemicellulose and starch citrate chitosan foam adsorbents for removal of arsenic and other heavy metals from contaminated water

Arsenic and other heavy metal contaminants in water are a significant global health threat. In this study, low-cost, sulfur-free, sustainable, water-insoluble materials with heavy metal remediation properties were produced from renewable resources such as starch, xylan, citric acid, and chitosan. Synthesized starch citrate-chitosan (SCC) foam and xylan citrate-chitosan (XCC) foam were flexible, porous, and elastic. The foams’ arsenic uptake in water was significantly greater than five different commercial metal remediating agents. The mercury and lead uptakes with the synthesized foams were similar to the performance of a commercial sulfur-based product, SorbaTech 450 (ST450). However, the cadmium and selenium uptakes were comparatively lower. The complexation of arsenic with oxygen and nitrogen of the SCC foam was shown with time-of-flight secondary ion mass spectrometry (TOF-SIMS). The XCC foam was also shown to adsorb potassium iodide (KI) at a similar rate to sodium chloride. This may be used to remediate water contaminated with radioactive materials, such as iodine 131.

Materials Science↗
DOE OSTI2020

Materials Data on Se by Materials Project

Se is alpha Selenium structured and crystallizes in the trigonal P3_121 space group. The structure is one-dimensional and consists of one Se ribbon oriented in the (0, 0, 1) direction. Se is bonded in a water-like geometry to two equivalent Se atoms. Both Se–Se bond lengths are 2.40 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Te by Materials Project

Te is alpha Selenium structured and crystallizes in the trigonal P3_121 space group. The structure is one-dimensional and consists of one Te ribbon oriented in the (0, 0, 1) direction. Te is bonded in a distorted water-like geometry to two equivalent Te atoms. Both Te–Te bond lengths are 2.89 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AsSe6IF6 by Materials Project

(Se)4AsSe2IF6 crystallizes in the monoclinic P2/c space group. The structure is one-dimensional and consists of eight selenium molecules and one AsSe2IF6 ribbon oriented in the (2, 0, 1) direction. In the AsSe2IF6 ribbon, As5+ is bonded in an octahedral geometry to six F1- atoms. There is two shorter (1.77 Å) and four longer (1.78 Å) As–F bond length. Se+0.33+ is bonded in a single-bond geometry to one I1- atom. The Se–I bond length is 2.76 Å. I1- is bonded in a 6-coordinate geometry to two equivalent Se+0.33+ and four F1- atoms. There are two shorter (3.56 Å) and two longer (3.68 Å) I–F bond lengths. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As5+ and one I1- atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As5+ and one I1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pd(SeCl3)2 by Materials Project

PdCl2(SeCl2)2 crystallizes in the monoclinic C2/c space group. The structure is zero-dimensional and consists of four palladium(ii) chloride molecules and eight selenium dichloride molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi2Se2Cl7 by Materials Project

Bi2Cl7(Se)2 crystallizes in the tetragonal P4/n space group. The structure is two-dimensional and consists of eight selenium molecules and one Bi2Cl7 sheet oriented in the (0, 0, 1) direction. In the Bi2Cl7 sheet, Bi+2.50+ is bonded in a 8-coordinate geometry to eight Cl1- atoms. There are a spread of Bi–Cl bond distances ranging from 2.63–3.37 Å. There are five inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Bi+2.50+ atom. In the second Cl1- site, Cl1- is bonded in a square co-planar geometry to four equivalent Bi+2.50+ atoms. In the third Cl1- site, Cl1- is bonded in a distorted tetrahedral geometry to four equivalent Bi+2.50+ atoms. In the fourth Cl1- site, Cl1- is bonded in a distorted water-like geometry to three equivalent Bi+2.50+ atoms. In the fifth Cl1- site, Cl1- is bonded in a water-like geometry to two equivalent Bi+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr(Se2Cl3)2 by Materials Project

Zr(SeCl3)2(Se)2 crystallizes in the orthorhombic Pccn space group. The structure is one-dimensional and consists of eight selenium molecules and two Zr(SeCl3)2 ribbons oriented in the (1, 1, 0) direction. In each Zr(SeCl3)2 ribbon, Zr2+ is bonded in an octahedral geometry to six Cl1- atoms. There are two shorter (2.45 Å) and four longer (2.52 Å) Zr–Cl bond lengths. Se1+ is bonded in a bent 120 degrees geometry to two Cl1- atoms. There are one shorter (2.97 Å) and one longer (2.99 Å) Se–Cl bond lengths. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Zr2+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Zr2+ and one Se1+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Zr2+ and one Se1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SeBr by Materials Project

SeBr crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four selenium bromide (se2br2) molecules. there are two inequivalent Se sites. In the first Se site, Se is bonded in a water-like geometry to one Se and one Br atom. The Se–Se bond length is 2.24 Å. The Se–Br bond length is 2.42 Å. In the second Se site, Se is bonded in a water-like geometry to one Se and one Br atom. The Se–Br bond length is 2.44 Å. There are two inequivalent Br sites. In the first Br site, Br is bonded in a single-bond geometry to one Se atom. In the second Br site, Br is bonded in a single-bond geometry to one Se atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge2C2(SeF2)3 by Materials Project

Ge2C2(SeF2)3 is diamond structured and crystallizes in the cubic Fd-3m space group. The structure is zero-dimensional and consists of eight selenium;trifluoromethylgermanium molecules. Ge4+ is bonded in a trigonal non-coplanar geometry to three equivalent Se2- atoms. All Ge–Se bond lengths are 2.38 Å. C2+ is bonded in a trigonal non-coplanar geometry to three equivalent F1- atoms. All C–F bond lengths are 1.36 Å. Se2- is bonded in a 2-coordinate geometry to two equivalent Ge4+ and two equivalent F1- atoms. Both Se–F bond lengths are 3.28 Å. F1- is bonded in a single-bond geometry to one C2+ and one Se2- atom.

36 MATERIALS SCIENCE↗