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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ho4NiB13 by Materials Project

Ho4NiB13 crystallizes in the tetragonal P4/mnc space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to fifteen B+1.15- atoms. There are a spread of Ho–B bond distances ranging from 2.55–2.89 Å. Ni3+ is bonded in a 8-coordinate geometry to eight equivalent B+1.15- atoms. All Ni–B bond lengths are 2.18 Å. There are three inequivalent B+1.15- sites. In the first B+1.15- site, B+1.15- is bonded in a cuboctahedral geometry to four equivalent Ho3+ and eight equivalent B+1.15- atoms. All B–B bond lengths are 2.10 Å. In the second B+1.15- site, B+1.15- is bonded in a 3-coordinate geometry to six equivalent Ho3+ and three B+1.15- atoms. There is two shorter (1.77 Å) and one longer (1.91 Å) B–B bond length. In the third B+1.15- site, B+1.15- is bonded in a 9-coordinate geometry to four equivalent Ho3+, one Ni3+, and four B+1.15- atoms. Both B–B bond lengths are 1.81 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Hydration structure and energetics of iron-exchanged montmorillonite

The interaction between iron released from corroded steel canisters and bentonite is a key process influencing the long-term performance of nuclear waste repositories. In particular, the migration of Fe²⁺ into montmorillonite (Mnt) interlayers may alter its hydration, swelling, and ion-transport properties. In the present study, molecular dynamics simulations were performed to investigate the hydration behavior, structural response, and transport properties of Fe-exchanged montmorillonite (Fe-Mnt) under varying hydration states. The simulations focus on short- to intermediate-time-scale Fe 2+ and Fe 3+ interlayer exchange and hydration effects, and do not consider long-term structural substitution, Fe-bearing clay phase stabilization, or secondary iron mineral precipitation. Systems containing Na + -, Fe 2+ -, and Fe 3+ -Mnt were examined using both periodic and edge-exposed configurations to evaluate interlayer structure, ion exchange, and free energy of Fe intercalation. The results show that Fe ions influence the interlayer spacing primarily at low water contents (<1 bilayer), where Fe-Mnt exhibits a d-spacing 1–2 Å larger than Na-Mnt due to stronger hydration. The calculated hydration energies follow the order Fe 2+ $<$Fe 3+ $<$Na + . Both water and ion diffusion coefficients decrease upon Fe ion intercalation, with Fe 2+ ions diffusing an order of magnitude more slowly than those of Na + . Free energy profiles further confirm that Fe 2+ and Fe 3+ ions are thermodynamically favored in the interlayer, with Fe 3+ being the most stable. In conclusion, these findings provide molecular-scale insights into the mechanisms of Fe–Na exchange and their implications for bentonite alteration in repository environments.

clay↗
DOE OSTI2022

Anisotropic magnon damping by zero-temperature quantum fluctuations in ferromagnetic CrGeTe 3

Spin and lattice are two fundamental degrees of freedom in a solid, and their fluctuations about the equilibrium values in a magnetic ordered crystalline lattice form quasiparticles termed magnons (spin waves) and phonons (lattice waves), respectively. In most materials with strong spin-lattice coupling (SLC), the interaction of spin and lattice induces energy gaps in the spin wave dispersion at the nominal intersections of magnon and phonon modes. Here we use neutron scattering to show that in the two-dimensional (2D) van der Waals honeycomb lattice ferromagnetic CrGeTe 3 , spin waves propagating within the 2D plane exhibit an anomalous dispersion, damping, and breakdown of quasiparticle conservation, while magnons along the c axis behave as expected for a local moment ferromagnet. These results indicate the presence of dynamical SLC arising from the zero-temperature quantum fluctuations in CrGeTe 3 , suggesting that the observed in-plane spin waves are mixed spin and lattice quasiparticles fundamentally different from pure magnons and phonons.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multipacting analysis of the SNS drift tube linac (DTL) RF vacuum window using Spark3d

An ongoing study at the Spallation Neutron Source (SNS) seeks to better understand and address potential multipacting issues associated with the Drift Tube Linac (DTL) RF vacuum windows. An analysis of several failed operational windows showed indications of excessive RF heating on the TiN-coated alumina ceramics. Coupled with vacuum bursts and arcing during conditioning and/or operational periods, these problems have been attributed to electron activity likely caused by multipacting. The status of the study, 3-D electromagnetic simulation results, mitigating techniques and a future experimental plan for studying multipacting in the SNS DTL vacuum windows are presented.

Toby, George↗
DOE OSTI2022

Gen 3 Particle Pilot Plant (G3P3) Life Cycle Management Plan (SAND report)

The National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories New Mexico (SNL/NM) developed this Life Cycle Management Plan (LCMP) to document its process for executing, monitoring, controlling and closing-out Phase 3 of the Gen 3 Particle Pilot Plant (G3P3). This plan serves as a resource for stakeholders who wish to be knowledgeable of project objectives and how they will be accomplished.

14 SOLAR ENERGY↗
DOE OSTI2020

Materials Data on Ho4CoB13 by Materials Project

Ho4CoB13 crystallizes in the tetragonal P4/mnc space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to fifteen B+1.15- atoms. There are a spread of Ho–B bond distances ranging from 2.56–2.89 Å. Co3+ is bonded in a 8-coordinate geometry to eight equivalent B+1.15- atoms. All Co–B bond lengths are 2.16 Å. There are three inequivalent B+1.15- sites. In the first B+1.15- site, B+1.15- is bonded in a cuboctahedral geometry to four equivalent Ho3+ and eight equivalent B+1.15- atoms. All B–B bond lengths are 2.11 Å. In the second B+1.15- site, B+1.15- is bonded in a 3-coordinate geometry to six equivalent Ho3+ and three B+1.15- atoms. There is two shorter (1.78 Å) and one longer (1.87 Å) B–B bond length. In the third B+1.15- site, B+1.15- is bonded in a 9-coordinate geometry to four equivalent Ho3+, one Co3+, and four B+1.15- atoms. Both B–B bond lengths are 1.80 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Te(HO)6 by Materials Project

Te(OH)6 crystallizes in the orthorhombic Fmm2 space group. The structure is two-dimensional and consists of two Te(OH)6 sheets oriented in the (0, 0, 1) direction. there are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.70 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.52 Å) H–O bond length. Te6+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Te–O bond distances ranging from 1.84–2.12 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to two equivalent H1+ and one Te6+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one H1+ and one Te6+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two H1+ and one Te6+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to two equivalent H1+ and one Te6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Ge2O7 by Materials Project

Ho2Ge2O7 crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with five equivalent GeO4 tetrahedra, edges with five equivalent HoO7 pentagonal bipyramids, and an edgeedge with one GeO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.23–2.56 Å. Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with five equivalent HoO7 pentagonal bipyramids, a cornercorner with one GeO4 tetrahedra, and an edgeedge with one HoO7 pentagonal bipyramid. There are a spread of Ge–O bond distances ranging from 1.76–1.80 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Ge4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Ge4+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three equivalent Ho3+ and one Ge4+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Syntheses and Crystal Structures of Rare-Earth Oxyapatites Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm)

Four different rare-earth oxyapatites of Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying, calcination, and high-temperature sintering in air. X-ray powder diffraction and Raman spectroscopy were performed on the synthesized oxyapatites. Here, the RE oxyapatites crystallize in the hexagonal space group P6 3 /m with similar unit cell parameters, increasing linearly with larger RE cations. The unit cell volumes increase linearly whereas the densities decrease nonlinearly with larger RE cations. Raman spectra showed intense bands of the symmetric bending and stretching modes of SiO 4 at ~ 400 and 860 cm -1 regions, respectively. The bands generally shifted to higher frequencies with smaller RE cations in the structures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Acousto-optic modulators of high-power laser radiation on the basis of KGW and KYW crystals

Different modifications of acousto-optic modulators (AOMs) based on KG(WO{sub 4}){sub 2} (KGW) and KY(WO{sub 4}){sub 2} (KYW) crystals, designed for Q switching of high-power pulsed lasers, is developed and investigated. It is shown that AOMs based on these crystals are universal, can be combined with different lasers in the wavelength range of 1 – 3 μm, and have a high radiation resistance in the absence of antireflection coatings and light input at Brewster’s angle. The operation efficiency of KGW-based AOMs is experimentally demonstrated. Solid-state lasers based on Cr : Er : YSGG (λ = 2.78 μm), Cr : Yb : Ho : YSGG (λ = 2.87 μm), Cr : Tm : Ho : YSGG (λ = 2.09 μm), and Nd : YAG (λ = 1.064 μm) crystals with active acousto-optic Q switching, operating in the repetitively pulsed regime with a high beam quality and without surface destruction, are investigated. Lasing pulses (30 – 60)-ns long with energy up to 32 mJ at a repetition rate from 1 to 1000 Hz are obtained. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Thermodynamic Understanding of Impurity Phase Segregation in a PdCrO 2 /CuCrO 2 Heterostructure

Abstract PdCrO 2 films are synthesized on CuCrO 2 buffer layers on Al 2 O 3 substrates. This synthesis is accompanied by impurity phase segregation, which hampers the synthesis of high quality PdCrO 2 films. Potential causes ofth impurity phase segregation are studied by using a combination of experiments and ab initio calculations. X‐ray diffraction and scanning transmission electron microscopy experiments reveal impurity phases of Cu x Pd 1 − x alloy and chromium oxides, Cr 2 O 3 and Cr 3 O 4 , in PdCrO 2 . Calculations determine that oxygen deficiency can cause the impurity phase segregation. Therefore, preventing oxygen release from delafossites can suppress the impurity phase segregation. The amounts of Cr 2 O 3 and Cr 3 O 4 depend on temperature and oxygen partial pressure. A reasonable theory‐based explanation for this experimental observation is provided.

2D metal↗
DOE OSTI2020

Materials Data on HoAgTe2 by Materials Project

HoAgTe2 crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. Ho3+ is bonded to six Te2- atoms to form HoTe6 octahedra that share corners with six equivalent AgTe4 tetrahedra, edges with six equivalent HoTe6 octahedra, and edges with three equivalent AgTe4 tetrahedra. There are three shorter (3.06 Å) and three longer (3.16 Å) Ho–Te bond lengths. Ag1+ is bonded to four Te2- atoms to form AgTe4 tetrahedra that share corners with six equivalent HoTe6 octahedra, corners with six equivalent AgTe4 tetrahedra, and edges with three equivalent HoTe6 octahedra. The corner-sharing octahedra tilt angles range from 11–58°. There are one shorter (2.79 Å) and three longer (2.83 Å) Ag–Te bond lengths. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to three equivalent Ho3+ and one Ag1+ atom to form distorted TeHo3Ag trigonal pyramids that share corners with six equivalent TeHo3Ag3 octahedra, corners with six equivalent TeHo3Ag trigonal pyramids, and edges with three equivalent TeHo3Ag3 octahedra. The corner-sharing octahedra tilt angles range from 3–67°. In the second Te2- site, Te2- is bonded to three equivalent Ho3+ and three equivalent Ag1+ atoms to form TeHo3Ag3 octahedra that share corners with six equivalent TeHo3Ag trigonal pyramids, edges with six equivalent TeHo3Ag3 octahedra, and edges with three equivalent TeHo3Ag trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KHo2Cl7 by Materials Project

KHo2Cl7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. K1+ is bonded in a 2-coordinate geometry to eight Cl1- atoms. There are a spread of K–Cl bond distances ranging from 3.16–3.78 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to seven Cl1- atoms to form a mixture of distorted face and edge-sharing HoCl7 pentagonal bipyramids. There are a spread of Ho–Cl bond distances ranging from 2.69–2.78 Å. In the second Ho3+ site, Ho3+ is bonded to seven Cl1- atoms to form a mixture of distorted face and edge-sharing HoCl7 pentagonal bipyramids. There are a spread of Ho–Cl bond distances ranging from 2.68–2.73 Å. There are seven inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 2-coordinate geometry to one K1+ and two Ho3+ atoms. In the second Cl1- site, Cl1- is bonded in a distorted trigonal non-coplanar geometry to one K1+ and two Ho3+ atoms. In the third Cl1- site, Cl1- is bonded in a 3-coordinate geometry to one K1+ and two Ho3+ atoms. In the fourth Cl1- site, Cl1- is bonded in a 2-coordinate geometry to two equivalent K1+ and two Ho3+ atoms. In the fifth Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to one K1+ and two Ho3+ atoms. In the sixth Cl1- site, Cl1- is bonded in a distorted water-like geometry to one K1+ and two Ho3+ atoms. In the seventh Cl1- site, Cl1- is bonded in a distorted trigonal non-coplanar geometry to one K1+ and two Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho3Si11Pt23 by Materials Project

Ho3Pt23Si11 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ho3+ is bonded to eight equivalent Pt+1.26- atoms to form distorted corner-sharing HoPt8 cuboctahedra. All Ho–Pt bond lengths are 3.16 Å. There are four inequivalent Pt+1.26- sites. In the first Pt+1.26- site, Pt+1.26- is bonded in a distorted square co-planar geometry to four equivalent Si+1.82+ atoms. All Pt–Si bond lengths are 2.58 Å. In the second Pt+1.26- site, Pt+1.26- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and three Si+1.82+ atoms. There are a spread of Pt–Si bond distances ranging from 2.43–2.46 Å. In the third Pt+1.26- site, Pt+1.26- is bonded to four Si+1.82+ atoms to form a mixture of edge and corner-sharing PtSi4 tetrahedra. There are one shorter (2.43 Å) and three longer (2.50 Å) Pt–Si bond lengths. In the fourth Pt+1.26- site, Pt+1.26- is bonded to four Si+1.82+ atoms to form a mixture of distorted edge and corner-sharing PtSi4 tetrahedra. All Pt–Si bond lengths are 2.51 Å. There are three inequivalent Si+1.82+ sites. In the first Si+1.82+ site, Si+1.82+ is bonded in a 7-coordinate geometry to seven Pt+1.26- atoms. In the second Si+1.82+ site, Si+1.82+ is bonded in a body-centered cubic geometry to eight Pt+1.26- atoms. In the third Si+1.82+ site, Si+1.82+ is bonded in a 7-coordinate geometry to seven Pt+1.26- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Origin of short- and medium-range order in supercooled liquid Ge 3 Sb 2 Te 6 from ab initio molecular dynamics simulations

Phase-change materials such as Ge–Sb–Te compounds have attracted much attention due to their potential value in electrical data storage. In contrast to the amorphous and crystalline phases, supercooled liquids are far from being deeply understood despite their inevitable role in both amorphization and crystallization processes. To this end, we have studied the dynamics properties and structural characteristics of liquid and supercooled liquid Ge 3 Sb 2 Te 6 during the fast cooling process. As the temperature decreases, chemical bonds become more homogeneous, but coordination numbers of Ge, Sb and Te atoms change very little. Meanwhile, the structural order of short-range configuration is obviously enhanced. Further studies suggest that Ge-centered, Sb-centered and Te-centered configurations change to the more ordered defective octahedrons mainly by adjusting the bond-angle relationship and bond length, rather than just by changing the coordination environment. It is the more ordered octahedrons that promote the formation of medium-range order. Our findings provide a deep insight into the origin of local structural order in supercooled liquid Ge 3 Sb 2 Te 6 , which is of great importance for the comprehensive understanding of amorphization and crystallization processes.

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

Study of an Integration Platform Based on an Adiabatic Active-Layer Waveguide Connection for InP Photonic Device Integration Mirroring That of Heterogeneous Integration on Silicon

In this work, a photonic device integration platform capable of integration of active-passive InP-based photonic devices without the use of material regrowth is introduced. The platform makes use of an adiabatic active-layer waveguide connection (ALWC) to move an optical beam between active and passive devices. The performance of this platform is analyzed using an example made up of four main sections: (1) a fiber coupling section for enabling vertical beam coupling from optical fiber into the photonic chip using a mode-matched surface grating with apodized duty cycles; (2) a transparent waveguide section for realizing passive photonic devices; (3) an adiabatic mode connection structure for moving the optical beam between passive and active device sections; and (4) an active device section for realizing active photonic devices. It is shown that the coupled surface grating, when added with a bottom gold reflector, can achieve a high chip-to-fiber coupling efficiency (CE) of 88.3% at 1550 nm. The adiabatic active-layer mode connection structure has an optical loss of lower than 1% (CE > 99%). The active device section can achieve an optical gain of 20 dB/mm with the use of only 3 quantum wells. The optimized structural parameters of the entire waveguide module are analyzed and discussed.

42 ENGINEERING↗
DOE OSTI2020

Materials Data on Na2HoPWO8 by Materials Project

Na2HoWPO8 is Esseneite-derived structured and crystallizes in the orthorhombic Ibca space group. The structure is three-dimensional. Na1+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Na–O bond distances ranging from 2.29–2.95 Å. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.28–2.45 Å. W6+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.81 Å) and two longer (1.83 Å) W–O bond length. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Na1+ and one W6+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Na1+, one Ho3+, and one P5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, two equivalent Ho3+, and one P5+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Na1+, one Ho3+, and one W6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoCuPbSe3 by Materials Project

HoCuPbSe3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share corners with two equivalent HoSe6 octahedra, corners with six equivalent PbSe7 pentagonal bipyramids, edges with two equivalent HoSe6 octahedra, edges with four equivalent PbSe7 pentagonal bipyramids, and edges with four equivalent CuSe4 tetrahedra. The corner-sharing octahedral tilt angles are 45°. There are a spread of Ho–Se bond distances ranging from 2.84–2.88 Å. Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with three equivalent PbSe7 pentagonal bipyramids, corners with two equivalent CuSe4 tetrahedra, edges with four equivalent HoSe6 octahedra, and edges with three equivalent PbSe7 pentagonal bipyramids. There are a spread of Cu–Se bond distances ranging from 2.44–2.52 Å. Pb2+ is bonded to seven Se2- atoms to form distorted PbSe7 pentagonal bipyramids that share corners with six equivalent HoSe6 octahedra, corners with three equivalent CuSe4 tetrahedra, edges with four equivalent HoSe6 octahedra, edges with two equivalent PbSe7 pentagonal bipyramids, edges with three equivalent CuSe4 tetrahedra, and faces with two equivalent PbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 24–66°. There are a spread of Pb–Se bond distances ranging from 3.15–3.29 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Ho3+, one Cu1+, and three equivalent Pb2+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to two equivalent Ho3+, one Cu1+, and two equivalent Pb2+ atoms. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent Ho3+, two equivalent Cu1+, and two equivalent Pb2+ atoms.

36 MATERIALS SCIENCE↗