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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Au 3 -to-Ag 3 coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

An efficient strategy for designing charge-transfer complexes using coinage metal cyclic trinuclear complexes (CTCs) is described herein. Due to opposite quadrupolar electrostatic contributions from metal ions and ligand substituents, [Au(m-Pz-(i-C 3 H7) 2 )] 3 ∙[Ag(m-Tz-(n-C 3 F 7 ) 2 )] 3 (Pz = pyrazolate, Tz = triazolate) has been obtained and its structure verified by single crystal X-ray diffraction – representing the 1st crystallographically-verified M 3 @M' 3 stacked adduct of monovalent coinage metal CTCs. Abundant supramolecular interactions with aggregate covalent bonding strength arise from a combination of M–M' (Au / Ag), metal–π, π–π interactions and hydrogen bonding in this charge-transfer complex, according to density functional theory analyses, yielding a computed binding energy of 66 kcal mol -1 between the two trimer moieties – a large value for intermolecular interactions between adjacent d 10 centres (nearly doubling the value for a recently claimed Au(I) / Cu(I) polar-covalent bond: Proc. Natl. Acad. Sci. U.S.A., 2017, 114, E5042) – which becomes 87 kcal mol -1 with benzene stacking. Surprisingly, DFT analysis suggests that: (a) some other literature precedents should have attained a stacked M 3 @M' 3 product akin to the one herein, with similar or even higher binding energy; and (b) a high overall intertrimer bonding energy by inferior electrostatic assistance, underscoring genuine orbital overlap between M and M' frontier molecular orbitals in such polar-covalent M–M' bonds in this family of molecules. The Au / Ag bonding is reminiscent of classical Werner-type coordinate-covalent bonds such as H 3 N: → Ag in [Ag(NH 3 ) 2 ] + , as demonstrated herein quantitatively. Solidstate and molecular modeling illustrate electron flow from the p-basic gold trimer to the p-acidic silver trimer with augmented contributions from ligand-to-ligand’ (LL'CT) and metal-to-ligand (MLCT) charge transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Synthesis of Antiperovskite Solid Electrolytes: Comparing Li 3 SI, Na 3 SI, and Ag 3 SI

Prior calculations have predicted that chalcohalide anti-perovskites may exhibit enhanced ionic mobility compared to oxyhalide anti-perovskites as solid-state electrolytes. Herein, the synthesis of Ag-, Li- and Na-based chalcohalide anti-perovskites is investigated using first-principle calculations and in situ synchrotron X-ray diffraction. These techniques demonstrate that the formation of Ag 3 SI is facilitated by the adoption of a common body centered cubic packing of S 2– and I – in the reactants and products at elevated temperatures, with additional stabilization achieved by the formation of a solid solution of the anions. Further, the absence of these two features appears to hinder the formation of the analogous Li and Na anti-perovskites.

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

Transport and optical properties of the chiral semiconductor Ag 3 AuSe 2

Previous band structure calculations predicted Ag 3 AuSe 2 to be a semiconductor with a band gap of approximately 1 eV. Here, we report single crystal growth of Ag 3 AuSe 2 and its transport and optical properties. Single crystals of Ag 3 AuSe 2 were synthesized by slow-cooling from the melt, and grain sizes were confirmed to be greater than 2 mm using electron backscatter diffraction. Optical and transport measurements reveal that Ag 3 AuSe 2 is a highly resistive semiconductor with a band gap and activation energy around 0.3 eV. Our first-principles calculations show that the experimentally determined band gap lies between the predicted band gaps from GGA and hybrid functionals. We predict band inversion to be possible by applying tensile strain. The sensitivity of the gap to Ag/Au ordering, chemical substitution, and heat treatment merit further investigation.

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

High-pressure characterization of Ag 3 AuTe 2 : Implications for strain-induced band tuning

Recent band structure calculations have suggested the potential for band tuning in the chiral semiconductor Ag 3 AuTe 2 to zero upon application of negative strain. In this study, we report on the synthesis of polycrystalline Ag 3 AuTe 2 and investigate its transport and optical properties and mechanical compressibility. Transport measurements reveal the semiconducting behavior of Ag 3 AuTe 2 with high resistivity and an activation energy E a of 0.2 eV. The optical bandgap determined by diffuse reflectance measurements is about three times wider than the experimental E a ⁠. Despite the difference, both experimental gaps fall within the range of predicted bandgaps by our first-principles density functional theory (DFT) calculations employing the Perdew–Burke–Ernzerhof and modified Becke–Johnson methods. Furthermore, our DFT simulations predict a progressive narrowing of the bandgap under compressive strain, with a full closure expected at a strain of –4% relative to the lattice parameter. To evaluate the feasibility of gap tunability at such substantial strain, the high-pressure behavior of Ag 3 AuTe 2 was investigated by in situ high-pressure x-ray diffraction up to 47 GPa. Mechanical compression beyond 4% resulted in a pressure-induced structural transformation, indicating the possibility of substantial gap modulation under extreme compression conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Enhanced hybridization in the electronic ground state of the intercalated honeycomb iridate Ag 3 LiIr 2 O 6

In this work, we use x-ray spectroscopy at the Ir L 3 /L 2 absorption edge to study powder samples of the intercalated honeycomb magnet Ag 3 LiIr 2 O 6 . Based on x-ray absorption and resonant inelastic x-ray scattering measurements, and exact diagonalization calculations including nearest-neighbor Ir-Ir electron hopping integrals, we argue that the intercalation of Ag atoms results in a delocalized electronic structure with enhanced Ir-O hybridization, departing from the local relativistic j eff =1/2 state. We find that the relative orbital contribution to the magnetic moment is increased and the magnetization density is spatially extended and asymmetric in this hybridized state. Our results confirm the importance of metal-ligand hybridization in the magnetism of transition metal oxides and provide empirical guidance for understanding the collective magnetism in intercalated honeycomb iridates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Signatures of a Majorana-Fermi surface in the Kitaev magnet Ag 3 LiIr 2 O 6

Detecting Majorana fermions in experimental realizations of the Kitaev honeycomb model is often complicated by non-trivial interactions inherent to potential spin liquid candidates. In this work, we identify several distinct thermodynamic signatures of massive, itinerant Majorana fermions within the well-established analytical paradigm of Landau-Fermi liquid theory. We find a qualitative and quantitative agreement between the salient features of our Landau-Majorana liquid theory and the Kitaev spin liquid candidate Ag 3 LiIr 2 O 6 . Our study presents strong evidence for a Fermi liquid-like ground state in the fundamental excitations of a honeycomb iridate, and opens new experimental avenues to detect itinerant Majorana fermions in condensed matter systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Ion redistributions at interfaces facilitate nucleation and growth of branched Ag 3 PO 4 polypods

Branched structures are of spectacular interest due to their improved light-harvesting, direct carrier transportation pathway, high surface area, and controllable electronic structures. Understanding their growth mechanisms and controlling factors enables the design of materials with improved functions. Interfaces of liquid-solid and air-liquid are known to change the chemical and physical properties of the liquid solution. However, their role in crystal growth, especially of branched structures, is seldom investigated. In this work we synthesized branched silver phosphate polypods in a thin layer of aqueous solution at room temperature taking advantage of the unique properties near the interfaces. The branched crystals nucleate and grow with a liquid thickness of 810 µm or below requiring the presence of both the gas-liquid and liquid-solid interfaces. The hydrophilicity of the solid substrate also facilitates nucleation and growth. Our results indicate that the synergism of long-range electric fields (ion distributions) at the interfaces promotes not only the nucleation and growth of silver phosphate but also the formation of branched structures. This work can be a reference for facilitating crystal nucleation and growth and controlling structures with specific morphologies, such as branched ones, by understanding and mimicking the properties at the interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In situ studies of reversible solid–gas reactions of ethylene responsive silver pyrazolates

Solid–gas reactions and in situ powder X-ray diffraction investigations of trinuclear silver complexes {[3,4,5-(CF 3 ) 3 Pz]Ag} 3 and {[4-Br-3,5-(CF 3 ) 2 Pz]Ag} 3 supported by highly fluorinated pyrazolates reveal that they undergo intricate ethylene-triggered structural transformations in the solid-state producing dinuclear silver–ethylene adducts. Despite the complexity, the chemistry is reversible producing precursor trimers with the loss of ethylene. Less reactive {[3,5-(CF 3 ) 2 Pz]Ag} 3 under ethylene pressure and low-temperature conditions stops at an unusual silver–ethylene complex in the trinuclear state, which could serve as a model for intermediates likely present in more common trimer–dimer reorganizations described above. Complete structural data of three novel silver–ethylene complexes are presented together with a thorough computational analysis of the mechanism.

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

First demonstration of tuning between the Kitaev and Ising limits in a honeycomb lattice

Recent observations of novel spin-orbit coupled states have generated interest in 4d/5d transition metal systems. A prime example is the J eff = $\frac{1}{2}$ state in iridate materials and α-RuCl 3 that drives Kitaev interactions. Here, by tuning the competition between spin-orbit interaction (λ SOC ) and trigonal crystal field (Δ T ), we restructure the spin-orbital wave functions into a previously unobserved μ = $\frac{1}{2}$ state that drives Ising interactions. This is done via a topochemical reaction that converts Li 2 RhO 3 to Ag 3 LiRh 2 O 6 . Using perturbation theory, we present an explicit expression for the μ = $\frac{1}{2}$ state in the limit Δ T ≫ λ SOC realized in Ag 3 LiRh 2 O 6 , different from the conventional J eff = $\frac{1}{2}$ state in the limit λ SOC ≫ Δ T realized in Li 2 RhO 3 . The change of ground state is followed by a marked change of magnetism from a 6 K spin-glass in Li 2 RhO 3 to a 94 K antiferromagnet in Ag 3 LiRh 2 O 6 .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag(Bi2S3)3 by Materials Project

Ag(Bi2S3)3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ag1+ is bonded to six S2- atoms to form AgS6 octahedra that share corners with two equivalent BiS6 octahedra, corners with four equivalent BiS5 square pyramids, edges with two equivalent AgS6 octahedra, and edges with six equivalent BiS5 square pyramids. The corner-sharing octahedral tilt angles are 55°. There are two shorter (2.51 Å) and four longer (2.98 Å) Ag–S bond lengths. There are three inequivalent Bi+2.83+ sites. In the first Bi+2.83+ site, Bi+2.83+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing BiS6 octahedra. The corner-sharing octahedra tilt angles range from 0–7°. There are a spread of Bi–S bond distances ranging from 2.75–2.95 Å. In the second Bi+2.83+ site, Bi+2.83+ is bonded to six S2- atoms to form BiS6 octahedra that share a cornercorner with one AgS6 octahedra, corners with three BiS6 octahedra, corners with two equivalent BiS5 square pyramids, and edges with seven BiS6 octahedra. The corner-sharing octahedra tilt angles range from 0–55°. There are a spread of Bi–S bond distances ranging from 2.68–3.10 Å. In the third Bi+2.83+ site, Bi+2.83+ is bonded to five S2- atoms to form BiS5 square pyramids that share corners with two equivalent AgS6 octahedra, corners with two equivalent BiS6 octahedra, edges with three equivalent AgS6 octahedra, and edges with four equivalent BiS5 square pyramids. The corner-sharing octahedra tilt angles range from 13–64°. There are one shorter (2.61 Å) and four longer (2.85 Å) Bi–S bond lengths. There are five inequivalent S2- sites. In the first S2- site, S2- is bonded to five Bi+2.83+ atoms to form SBi5 square pyramids that share corners with two equivalent SBi6 octahedra, corners with two equivalent SAgBi3 tetrahedra, edges with three equivalent SBi6 octahedra, and edges with four equivalent SBi5 square pyramids. The corner-sharing octahedral tilt angles are 4°. In the second S2- site, S2- is bonded to one Ag1+ and three Bi+2.83+ atoms to form distorted SAgBi3 tetrahedra that share a cornercorner with one SBi6 octahedra, corners with six SBi5 square pyramids, corners with three equivalent SAgBi3 tetrahedra, and edges with three equivalent SAg2Bi3 square pyramids. The corner-sharing octahedral tilt angles are 2°. In the third S2- site, S2- is bonded in a 3-coordinate geometry to three Bi+2.83+ atoms. In the fourth S2- site, S2- is bonded to two equivalent Ag1+ and three equivalent Bi+2.83+ atoms to form distorted SAg2Bi3 square pyramids that share corners with two equivalent SAg2Bi3 square pyramids, corners with four equivalent SAgBi3 tetrahedra, edges with five equivalent SAg2Bi3 square pyramids, and edges with three equivalent SAgBi3 tetrahedra. In the fifth S2- site, S2- is bonded to six Bi+2.83+ atoms to form SBi6 octahedra that share corners with four equivalent SBi5 square pyramids, corners with two equivalent SAgBi3 tetrahedra, edges with two equivalent SBi6 octahedra, and edges with six equivalent SBi5 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag(AsSe2)3 by Materials Project

Ag(AsSe2)2As(Se)2 crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two arsenic molecules; four selenium molecules; and one Ag(AsSe2)2 sheet oriented in the (0, 0, 1) direction. In the Ag(AsSe2)2 sheet, Ag1+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent Se2- atoms. All Ag–Se bond lengths are 2.68 Å. As+3.67+ is bonded in a linear geometry to two equivalent Se2- atoms. Both As–Se bond lengths are 2.39 Å. Se2- is bonded in a distorted linear geometry to one Ag1+, one As+3.67+, and one Se2- atom. The Se–Se bond length is 2.60 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag(NO2)3 by Materials Project

(Ag(NO3)2)2N2 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of four ammonia molecules and two Ag(NO3)2 sheets oriented in the (0, 0, 1) direction. In each Ag(NO3)2 sheet, Ag1+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Ag–O bond distances ranging from 2.19–2.91 Å. There are two inequivalent N+3.67+ sites. In the first N+3.67+ site, N+3.67+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.22 Å) and two longer (1.29 Å) N–O bond length. In the second N+3.67+ site, N+3.67+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.23–1.29 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Ag1+ and one N+3.67+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one Ag1+ and one N+3.67+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ag1+ and one N+3.67+ atom. In the fourth O2- site, O2- is bonded in a distorted L-shaped geometry to one Ag1+ and one N+3.67+ atom. In the fifth O2- site, O2- is bonded in a single-bond geometry to one N+3.67+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to one Ag1+ and one N+3.67+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag(BiSe2)3 by Materials Project

Ag(BiSe2)2Bi(Se)2 crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two bismuth molecules; four selenium molecules; and one Ag(BiSe2)2 sheet oriented in the (0, 0, 1) direction. In the Ag(BiSe2)2 sheet, Ag1+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent Se2- atoms. All Ag–Se bond lengths are 2.63 Å. Bi+3.67+ is bonded in a linear geometry to two equivalent Se2- atoms. Both Bi–Se bond lengths are 2.71 Å. Se2- is bonded in a distorted linear geometry to one Ag1+, one Bi+3.67+, and one Se2- atom. The Se–Se bond length is 2.51 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Solving the “Coloring Problem” in InPd 3– x Ag x ( x = 0–0.7) by Phase Diagrams Modeling and Diffraction Experiments

Here, a series of InPd 3–x Ag x (x = 0–1) compositions were synthesized by conventional high-temperature synthesis, and as-synthesized samples were characterized by powder X-ray diffraction experiments. Up to x = 0.7, InPd 3–x Ag x adopts the ternary substitutional variant of the InPd 3 structure (TiAl 3 -type), when x > 0.7, elemental Ag starts to segregate along with the main phase. Accurate structural characterization in InPd 3–x Ag x faces a critical challenge due to the narrow X-ray scattering contrast among constituents In, Pd, and Ag and nearly identical neutron scattering lengths of Pd and Ag. To overcome this “coloring problem”, a combination of calculation of phase diagrams modeling (CALPHAD) and diffraction techniques (X-ray and neutron) was employed. In the compositional range 0 ≤ x ≤ 0.7, InPd 3–x Ag x presents a ternary variant of the TiAl 3 -type structure, where Ag atoms selectively substitute one (the 2b Wyckoff site) of the two Pd sites in InPd 3 . Notably, in contrast to the isologous InPd 3–x Cu x (x = 0–1) system, Ag substitution does not form an ordered VRh 2 Sn-type structure at the limiting composition. The distinct site preference in InPd 3–x Ag x is elucidated by charge population analysis, electronic structure calculations, and orbital-resolved chemical bonding investigations, and the extent of substitution is supported by formation free energy calculations.

36 MATERIALS SCIENCE↗