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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Portable Distortion Free Large Solid Angle Coverage Detector

Neutron single crystal diffractometers require large solid angle coverage for optimum performance. This can be achieved by tiling flat detectors in a cylindrical or spherical geometry, but results in large gaps in detector coverage and parallax distortion. The detector edges exhibit degraded resolution, distortion, and gamma rejection. Since the detector edge regions are a significant fraction of the detector active area, they must be removed from the experimental data set, requiring extra beam time to collect enough analysis data. A spherical detector with a continuous surface would effectively address this issue while eliminating most boundary ‘dead’ areas. Here we report on the development of a novel hemispherical shaped neutron detector using seamlessly tiled readout modules to form the desired shape. The heart of the detector is a specially developed curved neutron scintillator coupled to high resolution silicon photomultiplier (SiPM) Anger cameras via custom made fiber optic tapers (FOTs). The detector has been assembled and initial tests have been conducted at the High Flux Isotope Reactor (HFIR) beamlines at Oak Ridge National Laboratory (ORNL). Here, in this work, we describe details of the scintillator design, fabrication and characterization, evaluation of individual detector modules, the details of the detector design implementation, and evaluation of the assembled detector at ORNL beamlines.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Precipitation of α' in neutron irradiated commercial FeCrAl alloys

In this paper, Alkrothal 720 and Kanthal APMT™, two commercial FeCrAl alloys, were neutron irradiated up to damage doses of 7.0 displacements per atom (dpa) in the temperature range of 320 to 382 °C to characterize the α' precipitation in these alloys using small-angle neutron scattering. Both alloys exhibited α' precipitation. Kanthal APMT™ exhibited higher number densities and volume fraction, a result attributed to its higher Cr content compared with Alkrothal 720. Finally, trends observed as a function of damage dose (dpa) are consistent with literature trends for both FeCr and FeCrAl alloys

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tuning color through sulfur and fluorine substitutions in the defect tin(II, IV) niobate pyrochlores

In this study, sulfur and fluorine substituted Sn 2 Nb 2 O 7 pyrochlore compounds were synthesized to produce brilliant orange/red colors as an environmentally friendly alternative to other toxic inorganic pigments. Neutron structure refinements indicate that the studied compositions crystallize in the pyrochlore structure with a large number of cation and/or anion vacancies and significant local structural disorder. The cubic unit cell decreases with increasing sulfur and fluorine content. The Sn 2+ cation is off-center by 0.39–0.48 Å from the ideal site, and the oxygen O' is strongly displaced to the 32e position by an extraordinarily large distance that has never been reported for a pyrochlore type phase. The unprecedented displacive disorder and unusual lattice evolution upon sulfur substitution are presumably driven by the strong lone pair stereoactivity associated with Sn 2+ . Chemical analysis confirmed the existence of sulfur and fluorine, and 119 Sn Mössbauer spectroscopy quantified the presence of both Sn 2+ and Sn 4+ in all compositions. The general formula representative of sulfur-containing pigments is nonstoichiometric Sn$2+\atop{2-z}$ (Nb 2-y Sn$4+\atop{y}$)O 7-z-y/2-x S x with the color varying according to x. The fluorine compound is refined to be Sn$2+\atop{2}$(Nb 0·958 Ti 0.984 Sn$4+\atop{0.058}$)O 6·376 F 0.206 with exclusively anion vacancies. Optical characterization was performed through diffuse reflectance and color meter measurements. The band gap is determined to be in the range of 2.35 to 2.05 eV as sample color changes from yellow to orange/red. Finally, all powder samples show 60–95% reflectance in the near-infrared (NIR) region, adding new functionality to the application of these compounds as “cool” pigments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Liquid-like solid-state diffusion of lithium ions in super-halide-rich argyrodite

The development of solid electrolytes with high ionic conductivity is essential for advancing safer, high-energy-density solid-state batteries, where lithium site distribution in the sublattice strongly affects ion transport. Here, we report a super-halide-rich argyrodite, Li 5.3 PS 4.3 Cl 1.7 , with remarkable room-temperature ionic conductivity (11.4 ± 0.7 mS cm -1 ) due to population of two additional interstitial lithium sites induced by vacancy redistribution. Prominent lithium density between lithium sites and elevated atomic displacement parameters indicate liquid-like diffusive behavior resembling sublattice melting. Combining electrochemical impedance spectroscopy, pulsed-field gradient NMR, and T 1 relaxation methods, we demonstrate that the augmented conductivity partly arises from a low energy barrier (0.08 eV) at the local scale, attributed to a three-site lithium distribution that drives correlated lithium dynamics. This work advances our understanding of the structure-dynamics interplay in super-halide-rich argyrodites, and highlighting their potential as solid-state battery electrolytes in cells with a coated single-crystal NMC82 cathode that achieve 170 mAh/g capacity at a 0.2 C rate .

25 ENERGY STORAGE↗
DOE OSTI2021

Thermal Evolution of Internal Strain in Doped PbTe

Recent improvements in the efficiency of heat-to-electricity energy conversion in lead chalcogenide thermoelectrics involve reducing the thermal conductivity by incorporating large amounts of internal strain. The extent to which typical lead chalcogenide processing techniques (such as doping, ball milling, and densification) increase internal strain and dislocation density must be quantified to improve materials design. In this study, neutron powder diffraction is leveraged to evaluate the internal strain introduced by ball milling in doped and undoped powders. Doping with Na and/or Eu increases internal strain beyond ball milling alone, with the greatest increase from combining the two dopants. Strain recovery occurs in each powder above 400 K but can be suppressed by co-doping, indicating a strong dopant–dislocation interaction in this system. Therefore, high-temperature processing of PbTe powders should be avoided if high internal strain is desired. Low-temperature densification and/or rapid pressing techniques may be key to maintaining internal strain in the final pressed pellet. The diffraction peak asymmetry and correlated elastic softening measured in pressed PbTe pellets in past studies were not observed in the precursor powders measured here, suggesting that measurements of the Debye temperature on final pressed pellets are required to examine the influence of defect-induced elastic softening on thermal conductivity. This work provides key guidance for defect engineering to maximize internal strain and thermoelectric performance in PbTe thermoelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The Impact of Structural Distortions on the Magnetism of Double Perovskites Containing 5d 1 Transition-Metal Ions

Five double perovskites, each containing a transition-metal ion with a 5d 1 configuration, have been studied to better understand the surprising diversity of magnetic ground states seen in these isoelectronic compounds. Ba 2 ZnReO 6 adopts the cubic double perovskite structure and magnetically orders below 16 K, with a canted ferromagnetic structure and a saturated magnetization of ~0.24 μ B /Re. X-ray magnetic circular dichroism indicates a substantial orbital moment of approximately 0.4 μ B /Re that opposes the spin moment. The structures of Ba 2 NaOsO 6 (canted ferromagnet, T C = 7 K) and Ba 2 LiOsO 6 (antiferromagnet, T N = 8 K) are reinvestigated using time-of-flight neutron powder diffraction and found to crystallize with the cubic double perovskite structure. No evidence for a structural distortion can be found in either compound down to 10 K. Ba 2 CdReO 6 is also cubic at room temperature but undergoes a structural transition upon cooling below ~180 K to a tetragonal structure with I4/m symmetry that involves compression of the Re–O bonds that are parallel to the c-axis. Sr 2 LiOsO 6 shows a similar tetragonal distortion at room temperature and maintains that structure down to 10 K. Surprisingly, the Os-centered octahedron in Sr 2 LiOsO 6 is distorted in the opposite direction, exhibiting an elongation of the Os–O bonds along the c-axis. Differences in the distortions of the octahedra lead to different magnetic ground states, antiferromagnetic (T N = 4 K) for Ba 2 CdReO 6 and spin glass (T g = 30 K) for Sr 2 LiOsO 6 . Theoretical modeling shows that the varied magnetic behaviors of double perovskites containing 5d 1 ions are closely tied to crystallographic distortions. Furthermore, these distortions remove the degeneracy of the 5d t 2g orbitals, leading to changes in orbital occupation that ultimately determine which of the several competing magnetic ground states is favored.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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 OSTI2016

Toward Molecule-Specific Geochemistry of Heavy Ends: Application to the Upstream Oil Industry

Detailed molecular analysis of the composition of petroleum is typically performed on only the light (volatile) fraction, using analyses involving gas chromatography (GC). Heavier (nonvolatile) components such as kerogen, bitumen, and asphaltenes, which are relevant to conventional reservoirs and particularly to unconventional gas shale and tight oil formations, are not amenable to analysis by GC and instead are typically studied by more phenomenological techniques. This report describes a suite of analytical techniques that can provide sufficient average molecular information on the heavy ends (defined as the nonvolatile fraction) to be useful for a variety of industrial applications, expanding the discipline of molecule-specific geochemistry into the non-GC amenable fractions of petroleum materials. Heavy ends are composed of the elements C, H, N, S, and O, and the bonding environments of each can be measured by various solid state spectroscopies: nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies for C, H, and O; X-ray absorption near-edge structure (XANES) spectroscopy for S and N. Additionally, advances in mass spectrometry, including techniques such as laser desorption laser ionization mass spectrometry (L2MS), can be used to measure the molecular weight and dominant molecular architecture of asphaltenes. Moreover, higher-order structures can be measured: samples of kerogen with representative pore geometry can be prepared, and those pore systems are analyzed with techniques such as X-ray diffraction and neutron scattering. Colloidal structures of asphaltenes can be measured with a variety of techniques, which reveal a hierarchical aggregation structure. These analyses provide sufficient structural data to enable structure–property and structure–function relationships to be determined, which can be applied to the characterization of conventional and unconventional resources. In gas shale and tight oil formations, which contain abundant inorganic minerals as well as kerogen, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is used for simultaneous analysis of mineralogy, kerogen content, and maturity, typically performed at the wellsite. In conventional reservoirs, spatial variations in the asphaltene concentration measured by downhole fluid analysis logging tools are being interpreted with a recently developed equation of state to address upstream issues such as reservoir connectivity, tar mat formation, and fault block migration. Furthermore, as more heavy end analyses are developed, further scientific knowledge and industrial applications of heavy end geochemistry are anticipated.

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

Effect of Local Structural Distortions on Antiferroelectric–Ferroelectric Phase Transition in Dilute Solid Solutions of K x Na 1– x NbO 3

The fundamental principles that govern antiferroelectric (AFE)–ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as K x Na 1– x NbO 3 ( x ≤ 0.02). Here, based on detailed structural analysis from neutron total scattering experiments, we provide insights about how the relative local distortions around the A- and B-sites of the ABO 3 perovskite structure affect the AFE/FE order of the average crystallographic phases in K x Na 1– x NbO 3 . Specifically, we show that a higher (lower) ratio of B-site-centered distortions over A-site-centered distortions drives transition toward a long-range FE (AFE) phase, which is based on a competition between the long-range polarizing field of the Nb–O dipoles and the disordering effect of local distortions around the A-site. Our study provides a predictive tool for designing complex solid-solution perovskites with tunable (anti)ferroelectric polarization properties, which can be of interest for various energy-related applications such as high-density energy storage and solid-state cooling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structural, Magnetic, and Optical Properties of A 3 V 4 (PO 4 ) 6 (A = Mg, Mn, Fe, Co, Ni)

Combined synchrotron and neutron powder diffraction indicates that A 3 V 4 (PO 4 ) 6 (A = Mg, Mn, Fe, Co, Ni) compounds crystallize with triclinic $P\bar{1}$ symmetry. Lattice parameters expand as expected with successive increases in the ionic radius of the A 2+ ion. Cation disorder on the octahedral sites increases as the ionic radii of A 2+ ion decreases. Direct-current magnetic susceptibility measurements indicate that all compounds with magnetic A 2+ ions order anti-ferromagnetically with transition temperatures ranging from 12 to 15 K. Effective magnetic moments for A 3 V 4 (PO 4 ) 6 (A = Mg, Mn, Fe, Co, Ni) are 5.16, 11.04, 10.08, 9.76, and 7.96 μ B per formula unit, respectively, in line with calculated values for high-spin transition metal ions. With the exception of Co 3 V 4 (PO 4 ) 6 the ultraviolet–visible spectra are dominated by d–d transitions of the V 3+ ions. Here, the striking emerald green color of Co 3 V 4 (PO 4 ) 6 arises from the combined effects of d–d transitions involving both V 3+ and Co 2+ .

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

CoSn-type NiIn1–xSbx (0 ≤ x ≤ 0.17): Site-Selective Substitution, Electronic Structure, Chemical Bonding, and Structural Transformation

CoSn-type intermetallic compounds have emerged as a model platform for Kagome-derived flat-band physics, where subtle chemical perturbations can strongly influence electronic structure and phase stability. Here, we present a combined experimental and theoretical study of Sb-substitution in CoSn-type NiIn1–xSbx (0 ≤ x ≤ 0.17) to elucidate the interplay between site selectivity, solubility limit, chemical bonding, and electronic structure. Rietveld refinements on Neutron powder diffraction data confirmed the selective Sb-substitution at the electron-rich In2 (2d) site forming the honeycomb substructure, while the In1 (1a) site within the Kagome layer remains exclusively occupied by In. Density functional theory (DFT) calculations revealed that pristine CoSn-type NiIn hosts Ni 3d-dominated flat bands near the Fermi level (EF), originating from the Kagome-like Ni substructure. Partial replacement of In by Sb within the honeycomb layer alters these flat-band features below EF, reducing the density of states and suppressing the flat-band topology near the Fermi level. Orbital-resolved electronic structure and chemical-bonding analyses show that Sb-substitution enhances Ni-p-block (In/Sb) covalency and optimizes charge compensation, stabilizing the CoSn-type structure up to the solubility limit x ≈ 0.17. Beyond the limit, the higher-Sb compositions show satellite reflections consistent with an incommensurately modulated phase. These results establish a link between site-selective chemical substitution, bonding optimization, and flat-band electronic structure evolution, providing fundamental insights into how chemical substitution influences the electronic properties of Kagome-based intermetallic compounds.

Roy, Nilanjan [National Institute of Technology Si↗
DOE OSTI2018

The Crystal Structure and Magnetic Behavior of Quinary Osmate and Ruthenate Double Perovskites La ABB 'O 6 ( A = Ca, Sr; B = Co, Ni; B ' = Ru, Os)

In this work, six LaABB'O 6 (A = Ca, Sr; B = Co, Ni; B' = Ru, Os) double perovskites were synthesized, several for the first time, and their crystal structures and magnetic behavior were characterized with neutron powder diffraction and direct-current and alternating-current magnetometry. All six compounds crystallize with P2 1 /n space group symmetry, resulting from a – a – c + octahedral tilting and complete rock salt ordering of transition-metal ions. Despite the electronic configurations of the transition-metal ions, either d 8 –d 3 or d 7 –d 3 , not one of the six compounds shows ferromagnetism as predicted by the Goodenough–Kanamori rules. LaSrNiOsO 6 , LaSrNiRuO 6 , and LaCaNiRuO 6 display long-range antiferromagnetic order, while LaCaNiOsO 6 , LaCaCoOsO 6 , and LaSrCoOsO 6 exhibit spin-glass behavior. These compounds are compared to the previously studied LaCaCoRuO 6 and LaSrCoRuO 6 , both of which order antiferromagnetically. Lastly, the observed variations in magnetic properties can be attributed largely to the response of competing superexchange pathways due to changes in B–O–B' bond angles, differences in the radial extent of the 4d (B' = Ru) and 5d (B' = Os) orbitals, and filling of the t 2g orbitals of the 3d ion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Magnetic Ground State Crossover in a Series of Glaserite Systems with Triangular Magnetic Lattices

The magnetic properties are reported for three members of the glaserite series of compounds, Na 2 BaM(VO 4 ) 2 , M = Mn, Mn 0.6 Co 0.4 , and Co. Large single crystals are grown using a high-temperature hydrothermal synthesis method. This structure type exhibits a triangular magnetic lattice in which M 2+ O 6 octahedra are interconnected with nonmagnetic (VO 4 ) 3– groups. All the structures crystallize at room temperature with rigid trigonal symmetry (space group $P\bar{3m}1$); however, at lower temperatures both Na 2 BaMn(VO 4 ) 2 and Na 2 BaMn 0.6 Co 0.4 (VO 4 ) 2 undergo a structural transition to lower symmetry (monoclinic, C2/c). The bulk magnetic measurements indicate that Mn- and Co-structures are antiferromagnetic and ferromagnetic, respectively. Na 2 BaMn 0.6 Co 0.4 (VO 4 ) 2 does not show any long-range ordering down to 0.5 K, although a broad heat capacity anomaly near 1.2 K suggests short-range magnetic order or freezing into a spin-glass-like state related to the chemical disorder and resulting competing magnetic interactions. The magnetic structures of Na 2 BaMn(VO 4 ) 2 and Na 2 BaCo(VO 4 ) 2 were determined using neutron powder diffraction. At zero magnetic field, Na 2 BaMn(VO 4 ) 2 possesses an antiferromagnetic structure with the moments ordered in a Néel-type arrangement and aligned along the C 4 axis of the octahedra. Under applied magnetic field at 0.3 K, the evolution of the magnetic structure toward a fully polarized state is observed. Na 2 BaCo(VO 4 ) 2 represents a ferromagnetic (FM) magnetic structure with Co moments aligned parallel to the c-axis direction. Finally, the relationships between these structures and magnetic properties are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Role of f Electrons in the Optical and Photoelectrochemical Behavior of Ca(La 1– x Ce x ) 2 S 4 (0 ≤ x ≤ 1)

This study focuses on a solid solution series, Ca(La 1– x Ce x ) 2 S 4 (0 ≤ x ≤ 1), where the f electron density is absent in CaLa 2 S 4 and is progressively increased until it is maximized in CaCe 2 S 4 . Correspondingly, these samples, synthesized by a sealed ampule method, showed progressive variations in color ranging from gray for CaLa 2 S 4 to orange-red for CaCe 2 S 4 . The crystal structural nuances of both the end members and three solid solutions with $x$ = 0.25, 0.50, and 0.75 were established with the complementary use of synchrotron X-ray diffraction and neutron scattering. Interestingly, these data were consistent with a two-phase composition centered around each nominal solid solution stoichiometry. Optical characterization via diffuse reflectance spectroscopy and Tauc analyses showed a shrinking of the energy band gap (from the UV to vis range) when Ce was progressively introduced into the host CaLa 2 S 4 structure. Overall, these data were in concert with electronic band structure calculations, using density functional theory, which showed the progressive formation of an intermediate f band when Ce was introduced intro the structure. Photoelectrochemical measurements in an aqueous redox electrolyte, as well as surface photovoltage and Kelvin probe measurements, revealed all samples to be n-type semiconductors. The valence and conduction band edge positions of the end members and the three solid solutions could be mapped, on both the redox and vacuum reference energy scales, by combining these measurements with the optical data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗