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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Stabilization Of The CN 3 5− Anion In Recoverable High‐pressure Ln 3 O 2 (CN 3 ) (Ln=La, Eu, Gd, Tb, Ho, Yb) Oxoguanidinates

Abstract A series of isostructural Ln 3 O 2 (CN 3 ) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high‐pressure (25–54 GPa) high‐temperature (2000–3000 K) conditions in laser‐heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single‐crystal X‐ray diffraction (SCXRD) as well as corroborated by X‐ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln 3 O 2 (CN 3 ) solids are composed of the hitherto unknown CN 3 5− guanidinate anion—deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln 3 O 2 (CN 3 ) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln 3 O 2 (CN 3 ) compounds are recoverable to ambient conditions. The stabilization of the CN 3 5− guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry.

Chemistry↗
DOE OSTI2022

Evolution of Physical Properties of RE 3 Ni 5 Al 19 Family (RE = Y, Nd, Sm, Gd, Tb, Dy, Ho, and Er)

In this study, single crystals of RE 3 Ni 5 Al 19 series (RE = Y, Nd, Sm, Gd, Tb, Dy, Ho, and Er) are grown using the Al self-flux method. The crystal structure is examined by both single crystal and powder X-ray diffraction. Physical properties are studied for the first time for RE 3 Ni 5 Al 19 (RE = Y, Nd, Gd, Tb, Dy, Ho, and Er) by means of magnetic susceptibility, electrical resistivity, and heat capacity measurements. Complex magnetic behaviors, with up to three transitions present for RE = Sm, Gd, Tb, and Dy, are revealed. Y 3 Ni 5 Al 19 is found to be a nonmagnetic nonsuperconducting metal (above T = 1.8 K) with weak electron–phonon coupling strength.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Structure and thermodynamics of calcium rare earth silicate oxyapatites, Ca 2 RE 8 (SiO 4 ) 6 O 2 (RE = Pr, Tb, Ho, Tm)

Calcium rare earth silicate oxyapatites, (Ca 2 RE 8 (SiO 4 ) 6 O 2 ), are of interest as components of glass-ceramic nuclear waste forms. To assess their long-term behavior in a geologic repository, it is essential to determine their structure and thermodynamic stability at relevant conditions. Here, in this work, we performed detailed structural and thermodynamic investigations on Ca 2 Pr 8 (SiO 4 ) 6 O 2 , Ca 2 Tb 8 (SiO 4 ) 6 O 2 , Ca 2 Ho 8 (SiO 4 ) 6 O 2 , and Ca 2 Tm 8 (SiO 4 ) 6 O 2 by high energy synchrotron powder X-ray diffraction combined with Rietveld analysis and high temperature oxide melt drop solution calorimetry. Enthalpies of formation from constituent oxides (ΔH f,ox ) were determined to be -765.1 ± 22.8 kJ/mol for Ca 2 Pr 8 (SiO 4 ) 6 O 2 ; -638.9 ± 20.5 kJ/mol for Ca 2 Tb 8 (SiO 4 ) 6 O 2 ; -643.3 ± 10.3 kJ/mol for Ca 2 Ho 8 (SiO 4 ) 6 O 2 ; and -403.2 ± 5.1 kJ/mol for Ca 2 Tm 8 (SiO 4 ) 6 O 2 . These thermodynamic parameters were used in assessing the thermochemical stability of these phases in the presence of water vapor from room temperature to 600 K, as encountered in the subsurface environments of a geological repository.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Theoretical kinetics predictions for NH 2 + HO 2

Recent modeling studies of NH 3 oxidation, which are motivated by the prospective role of ammonia as a zero-carbon fuel, have indicated significant discrepancies between existing literature mechanisms. In this study high level theoretical kinetics predictions have been obtained for the reaction of NH 2 with HO 2 , which has previously been highlighted as an important reaction with high sensitivity and high uncertainty. The potential energy surface is explored with coupled cluster calculations including large basis sets and high-level corrections to yield high accuracy (~0.2 kcal/mol) estimates of the stationary point energies. Variational transition state theory is used to predict the microcanonical rate constants, which are then incorporated in master equation treatments of the temperature and pressure dependent kinetics. For the radical-radical channels, the microcanonical rates are obtained from variable reaction coordinate transition state theory implementing directly evaluated multireference electronic energies. The analysis yields predictions for the total rate constant as well as the branching to the NH 3 + O 2 , H 2 NO + OH, and HNO + H 2 O channels. Rate constants are also reported for the H 2 NO + OH reaction as they arise naturally from the analysis. The rate constant and branching fraction determined in this work for the NH 2 + HO 2 reaction deviate significantly from values used in most previous modeling studies. The fact that the main product channel is chain terminating, rather than propagating, has strong implications for modeling NH 3 ignition and oxidation, in particular at intermediate temperatures and elevated pressure.

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

Transition from an incommensurate spin density wave to a commensurate magnetic order in a triangular lattice compound Ho 2 PdAl 6 Ge 4

Rare-earth (RE) intermetallics on a triangular lattice are promising candidates for generating interesting magnetic phases due to the complex interplay between Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and geometrical frustration. Here, in this work, we report the exotic magnetic structure of a layered compound Ho 2 PdAl 6 Ge 4 with triangular lanthanide nets. Magnetization and heat capacity measurements in zero magnetic field reveal two magnetic phase transitions at T N1 = 10.8 K and T N2 = 6.0 K. Neutron powder diffraction demonstrates a commensurate antiferromagnetic phase with k 1 = (0, 0, 1.5) below T N2 . With increasing temperature, another incommensurate vector appears and therefore, the magnetic structure of the intermediate state is identified as an unusual incommensurate spin density wave with two propagation vectors k 1 = (0, 0, 1.5) and k 2 = (0.0492, 0.0492, 1.5). The magnetic moments in the intermediate state rotate continuously and form an unusual S-shaped wave arrangement in the ab plane, sharing similarities with typical cycloid and helix magnetic orders. These results identify Ho 2 PdAl 6 Ge 4 as a candidate for exploring field-induced topological magnetic phases such as skyrmions, opening the way for further investigations on the family of RE 2 PdAl 6 Ge 4 materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mode Specificity in the OH + HO 2 → H 2 O + O 2 Reaction: Enhancement of Reactivity by Exciting a Spectator Mode

A reaction usually involves a few active modes while the other modes are largely preserved throughout the reaction as spectators. Excitation of an active mode is expected to promote the reaction, but depositing energy in a spectator mode typically has no effect, because of the differing ability for energy flow to the reaction coordinate. Here, we report a surprising case of mode specificity in a key radical–radical reaction OH + HO 2 → H 2 O + O 2 , where such canonical expectations fail to hold. Despite its spectator nature, the vibrational excitation of the OH reactant is shown at low collision energies to enhance the reactivity significantly. This unique effect can be attributed to the increased attraction with HO 2 due to the larger dipole of the stretched OH. At low collision energies, the stronger attraction increases the chance of capturing the reactants to form a hydrogen-bonded complex, thus of passing through the submerged barrier. The novel mechanism differs from the conventional vibrational enhancement via coupling to the reaction coordinate at the transition state, enriching our understanding of mode specificity in chemistry.

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

Probing time-resolved plasma-driven solution electrochemistry in a falling liquid film plasma reactor: Identification of HO$^−_2$ as a plasma-derived reducing agent

Many applications involving plasma–liquid interactions depend on the reactive processes occurring at the plasma–liquid interface. In this article, we report on a falling liquid film plasma reactor allowing for in situ optical absorption measurements of the time-dependence of the ferricyanide/ferrocyanide redox reactivity, complemented with ex situ measurement of the decomposition of formate. We found excellent agreement between the measured decomposition percentages and the diffusion-limited decomposition of formate by interfacial plasma-enabled reactions, except at high pH in thin liquid films, indicating the involvement of previously unexplored plasma-induced liquid phase chemistry enabled by long-lived reactive species. We also determined that high pH facilitates a reduction-favoring environment in ferricyanide/ferrocyanide redox solutions. In situ conversion measurements of a 1:1 ferricyanide/ferrocyanide redox mixture exceed the measured ex situ conversion and show that conversion of a 1:1 ferricyanide/ferrocyanide mixture is strongly dependent on film thickness. We identified three dominant processes: reduction faster than ms time scales for film thicknesses >100 µm, •OH-driven oxidation on time scales of <10 ms, and reduction on 15 ms time scales for film thickness <100 µm. We attribute the slow reduction and larger formate decomposition at high pH to HO$^−_2$ formed from plasma-produced H 2 O 2 enabled by the high pH at the plasma–liquid interface as confirmed experimentally and by computed reaction rates of HO$^−_2$ with ferricyanide. Overall, this work demonstrates the utility of liquid film reactors in enabling the discovery of new plasma-interfacial chemistry and the utility of atmospheric plasmas for electrodeless electrochemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Anomalous and planar Hall effects in Co 1−x Ho x thin films across the magnetic sublattice compensation temperature

Metallic amorphous ferrimagnets derived from alloying 3d transition metals with 4f-electron rare earths host fascinating effects of compensation between the 3d and 4f magnetic sublattices. Here, a detailed study of the anisotropic magnetoresistance (Δρ xx ), planar Hall effect (ρ xy PHE ), and anomalous Hall effect (ρ xy AHE ) is reported on a series of Co 1−x Ho x thin films over a wide field–temperature (H–T) phase space. Close to the magnetic compensation temperature, the ρ xy AHE –H loops show a double sign reversal and signatures of spin-flop transition at higher fields. The Δρ xx and ρ xy PHE also display strong deviations from the classical angular dependence seen in soft ferromagnets like permalloy as the angle ϕ between in-plane current and magnetic field is scanned from 0 to 2π. It is argued that the non-zero orbital angular momentum of Ho ions in the lattice and stabilization of bubble domains below magnetic saturation may be responsible for such features. Direct imaging of magnetic textures with x-ray photoelectron microscopy shows the formation of stripe domain patterns in the regime of sublattice compensation. Such stripes are likely to transform into magnetic bubbles before full saturation is reached in a large magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Lasing characteristics of ZrO{sub 2} − Y{sub 2}O{sub 3} − Ho{sub 2}O{sub 3} crystals pumped by a Tm : LiYF{sub 4} laser

Two-micron lasing is obtained on the {sup 5}I{sub 7} → {sup 5}I{sub 8} transition of Ho{sup 3+} ions in ZrO{sub 2} − Y{sub 2}O{sub 3} −Ho{sub 2}O{sub 3} crystals upon resonance pumping into the {sup 5}I{sub 7} level of these ions by a pulsed laser based on a Tm : LiYF{sub 4} crystal. The efficiency of conversion of pump radiation incident on the crystal to laser radiation and the slope lasing efficiency at a pulse duration of 8 ms and a pulse repetition rate of 10 Hz were 25% and 28%, respectively. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2026

Multiple valence-space and core-excited band terminations in Ho and Er isotopes

High-spin structures of holmium (𝑍 = 67) and erbium (𝑍 = 68) isotopes are presented near mass 160, a region where collective and single-particle modes of excitation compete in the generation of angular momentum at the highest experimentally attainable spins in atomic nuclei. The level schemes of the 156,157,158 Ho isotopes have been significantly extended, reaching spins in the 40⁢ℏ to 55⁢ℏ range, through multiple experiments utilizing the Gammasphere spectrometer. In particular, several new noncollective band-terminating states are reported for these nuclei. The nature of these states, including both valence-space terminations and core-excited oblateconfigurations, is discussed in terms of proton particle-hole (p-h) excitations across the semimagic 𝑍 = 64 shell closure. Cranked-Nilsson–Strutinsky (CNS) calculations have been used to interpret the nature of these noncollective states. The corresponding terminating states in 154–159 Er are also included, providing a systematic description of band termination in this mass region. In addition, three weak rotational structures have been assigned to 157 Ho at the highest spins. These collective bands are proposed to be based on a triaxial strongly deformed nuclear shape, involving neutron p-h excitations across the 𝑁 = 82 shell gap.

150 ≤ A ≤ 189↗
DOE OSTI2020

Cooperative Ru(4 d )–Ho(4 f ) magnetic ordering and phase coexistence in the 6 H perovskite multiferroic Ba 3 HoRu 2 O 9

We report cooperative magnetic orderings in a 6H-perovskite multiferroic system, Ba 3 HoRu 2 O 9 , via comprehensive neutron powder diffraction measurements. This system undergoes long-range antiferromagnetic ordering at T N1 ~ 50 K with a propagation wave vector of K 1 = (0.5 0 0), a transition temperature much higher than the previously reported one at ~10 K (T N2 ). Both Ru and Ho-moments order simultaneously below T N1 , followed by spin-reorientations at lower temperatures, demonstrating strong Ru(4d)-Ho(4f) magnetic correlation. Below T N1 another magnetic phase with a propagation wave vector K 2 = (0.25 0.25 0) emerges and coexists with the one associated with K 1 , which is rarely observed and suggests complex magnetism due to phase competition in the magnetic ground state. Here, we argue that the exchange-striction arising from the up-up-down-down spin structure associated with K 2 below T N2 may be responsible for the small ferroelectric polarization reported previously in this compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Effects of triaxiality and residual n p interaction in the proton emission from Ho 140

Here we present a detailed theoretical investigation of proton emission from 140 Ho within the nonadiabatic quasiparticle approach. The calculated proton emission half-life reproduces well the measured data. The importance of triaxiality and of the residual np interaction are studied. The ground state spin and parity of 139 Dy (daughter) and 140 Ho (parent) are ascertained unambiguously as 7/2 + and 3 – , respectively, by analyzing the rotational energies, half-lives, and branching ratios.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Low-Energy Electron Elastic Total Cross Sections for Ho, Er, Tm, Yb, Lu, and Hf Atoms

The robust Regge-pole methodology wherein is fully embedded the essential electron-electron correlation effects and the vital core polarization interaction has been used to explore negative ion formation in the large lanthanide Ho, Er, Tm, Yb, Lu, and Hf atoms through the electron elastic total cross sections (TCSs) calculations. These TCSs are characterized generally by dramatically sharp resonances manifesting ground, metastable, and excited negative ion formation during the collisions, Ramsauer-Townsend minima, and shape resonances. The novelty and generality of the Regge-pole approach is in the extraction of the negative ion binding energies (BEs) of complex heavy systems from the calculated electron TCSs. The extracted anionic BEs from the ground state TCSs for Ho, Er, Tm, Yb, Lu, and Hf atoms are 3.51 eV, 3.53 eV, 3.36 eV, 3.49 eV, 4.09 eV and 1.68 eV, respectively. The TCSs are presented and the extracted from the ground; metastable and excited anionic states BEs are compared with the available measured and/or calculated electron affinities. We conclude with a remark on the existing inconsistencies in the meaning of the electron affinity among the various measurements and/or calculations in the investigated atoms and make a recommendation to resolve the ambiguity.

Felfli, Zineb↗
DOE OSTI2020

Materials Data on Ho(NiP)2 by Materials Project

HoNi2P2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho3+ is bonded in a distorted body-centered cubic geometry to eight equivalent P3- atoms. All Ho–P bond lengths are 2.96 Å. Ni+1.50+ is bonded to four equivalent P3- atoms to form a mixture of edge and corner-sharing NiP4 tetrahedra. All Ni–P bond lengths are 2.27 Å. P3- is bonded in a 9-coordinate geometry to four equivalent Ho3+, four equivalent Ni+1.50+, and one P3- atom. The P–P bond length is 2.29 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(FeSi)2 by Materials Project

HoFe2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Ho–Si bond lengths are 3.07 Å. Fe+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing FeSi4 tetrahedra. All Fe–Si bond lengths are 2.26 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Ho3+, four equivalent Fe+2.50+, and one Si4- atom. The Si–Si bond length is 2.54 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(CuSi)2 by Materials Project

HoCu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Ho–Si bond lengths are 3.03 Å. Cu+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CuSi4 tetrahedra. All Cu–Si bond lengths are 2.38 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Ho3+, four equivalent Cu+2.50+, and one Si4- atom. The Si–Si bond length is 2.34 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(SiOs)2 by Materials Project

HoOs2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight equivalent Os+1.50- atoms. All Ho–Os bond lengths are 3.19 Å. Os+1.50- is bonded in a 4-coordinate geometry to four equivalent Ho3+ and four equivalent Si atoms. All Os–Si bond lengths are 2.40 Å. Si is bonded in a 5-coordinate geometry to four equivalent Os+1.50- and one Si atom. The Si–Si bond length is 2.46 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(SiRu)2 by Materials Project

HoRu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to eight equivalent Si4- atoms. All Ho–Si bond lengths are 3.21 Å. Ru+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing RuSi4 tetrahedra. All Ru–Si bond lengths are 2.38 Å. Si4- is bonded in a 4-coordinate geometry to four equivalent Ho3+ and four equivalent Ru+2.50+ atoms.

36 MATERIALS SCIENCE↗