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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 OSTI2021

Elucidating the Location of Cd 2+ in Post-synthetically Treated InP Quantum Dots Using Dynamic Nuclear Polarization 31 P and 113 Cd Solid-State NMR Spectroscopy

Indium phosphide quantum dots (InP QD) are a promising alternative to traditional QD materials that contain toxic heavy elements such as lead and cadmium. However, InP QD obtained from colloidal synthesis are often plagued by poor photoluminescence quantum yields (PL-QYs). In order to improve the PL-QY of InP QD, a number of post-synthetic treatments have been devised. Recently, it has been shown that InP post-synthetically treated with Lewis acid metal divalent cations (M-InP) exhibit enhanced PL-QY; however, the molecular structure and mechanism behind the improved PL-QY are not fully understood. Here, to determine the surface structure of M-InP QD, dynamic nuclear polarization surface-enhanced nuclear magnetic resonance spectroscopy (DNP SENS) experiments were employed on a series of InP magic size clusters treated with Cd ions, InP QD, cadmium phosphide (Cd 3 P 2 ) QD, and Cd-treated InP QD (Cd–InP QD). With the use of DNP SENS, we were able to obtain the 1D 31 P and 113 Cd NMR spectra, 113 Cd{ 31 P} rotational-echo double-resonance (REDOR) NMR spectra, and 31 P{ 113 Cd} dipolar heteronuclear multiple quantum correlation (D-HMQC) sequence. Changes in the phosphide 31 P chemical shifts after Cd treatment provide indirect evidence that some Cd alloys into the sub-surface regions of the particle. DNP-enhanced 113 Cd solid-state NMR spectra suggest that most Cd ions are coordinated by oxygen atoms from either carboxylate ligands or surface phosphate groups. 113 Cd{ 31 P} REDOR and 31 P{ 113 Cd} D-HMQC experiments confirm that a subset of Cd ions are located on the surface of Cd–InP QD and coordinated with phosphate groups.

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

Synthesis and structural characterization of the new Zintl phases Ba 3 Cd 2 P 4 and Ba 2 Cd 2 P 3 . Rare example of small gap semiconducting behavior with negative thermopower within the range 300 K-700 K

The new Zintl phases Ba 3 Cd 2 P 4 and Ba 2 Cd 2 P 3 have been synthesized using Pb flux, which allowed for the growth of 4-5 mm large crystals. The structures were determined utilizing single-crystal X-ray diffraction methods. Both compounds crystalize in the monoclinic crystal system (space group C2/m (No. 12)) and their structures are closely related. The structure of Ba 3 Cd 2 P 4 can be seen as being comprised of divalent Ba atoms and conjoined CdP 4 tetrahedra in the form of [Cd 2 P 4 ] 6- layers. Within the layers, homoatomic P–P bonds are present, which if cleaved, leave two infinite [CdP 3 ] 7- chains running along the crystallographic b-axis. The other structure, that of Ba 2 Cd 2 P 3 , can be rationalized as also having divalent Ba atoms and conjoined CdP4 tetrahedra in the form of [Cd 2 P 3 ] 6- layers. These layers, again, can be visualized as chains that run down the crystallographic b-axis, which are further connected by P-P dimers. Electronic band structure calculations show that each structure has an optimal number of valence electrons, and therefore conform to the Zintl-Klemm concept. Accordingly, the two compounds can be considered small band gap semiconductors, with band gaps of ca. 0.1 eV and 0.6 eV for Ba3Cd2P4 and Ba 2 Cd 2 P 3 , respectively. Electrical resistivity measurements show that Ba3Cd2P4 displays a large resistivity value at room temperature and an experimental band gap of ca. 0.05 eV, which fits reasonably well with the theoretical predictions. Thermopower measurements show that throughout the temperature range 300 K-700 K, Ba 3 Cd 2 P 4 displays a negative Seebeck coefficient. Here, the extremum value of -84 μV is reached at 630 K, suggestive of an n-type semiconductor, a rarity among Zintl phases.

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

Effect of Cd on the Nucleation and Transformation of Amorphous Calcium Carbonate

Qualitative measurements observations and field observations measurements indicate mineral coatings are one of the most abundant ways earth materials form, including in sedimentary deposits and certain biominerals. Formation of amorphous carbonates and other metastable intermediates in such these mixed cation systems is poorly understood, however. Using in situ PDF and SAXS, along with ICP-MS and SEM, results from this study 1) determines identify a novel short-range ordered Cd-ACC phase and 2) finds determine amorphous carbonate is stabilized by Cd2+, and 3) support formation of Cd-substituted vaterite, a polymorph of Ca that is not natively formed by Cd CO3. Results are highly dependent on ACC supersaturation, suggesting Cd-induced stability of Cd-ACC are is dependent primarily very sensitive on amorphous phase kinetics rather than thermodynamics to the rate of Cd-ACC nucleation and transformation. Findings provide a quantitative understanding of precursor intermediate phase structure and stability in mixed cation carbonate systems and aggregation that impact and suggest alternate pathways to forming the chemical heterogeneities frequently observed in natural mineral coatings.

Mergelsberg, Sebastian T.↗
DOE OSTI2022

Vibrational modes and crystallographic structure of Cd 3 As 2 and (Cd 1-x Zn x ) 3 As 2 epilayers

Low-temperature Raman scattering is used to study the crystal structure of molecular-beam epitaxially grown layers of the Dirac semimetal Cd 3 As 2 and its related alloy (Cd 1-x Zn x ) 3 As 2 . The combination of narrow-linewidth spectra, multiple growth directions and full polarization analysis allows improved accuracy in identifying the irreducible representation of over 57 Raman-active vibrations. Several disagreements with previous identifications are found. Structurally, the results agree with the centrosymmetric I41/acd space group of bulk-grown Cd 3 As 2 and are clearly distinct from the Raman spectra of nanoscale platelets and wires. Three-fold twinning is seen in (112) Cd 3 As 2 grown on (111) zincblende substrates corresponding to the three possible tetragonal orientations. In dilute (Cd 1-x Zn x ) 3 As 2 , phonons have a frequency and scattering amplitude dependence on Zn concentration that is continuous with Cd 3 As 2 but at least one frequency is absent at the alloy endpoint, preventing a simple one-mode description of the alloy phonon.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Oxygen Management to Avoid Photo-Inactive Cd(S,Se) for Efficient Cd(Se,Te) Solar Cells

Our previous work has demonstrated that the formation of a penternary cadmium chalcogenide Cd(O,S,Se,Te) region can significantly reduce the front interface recombination in Cd(Se,Te)-based thin-film solar cells. In this work, we have shown that oxygen management during the device fabrication is crucial to form this region. While both the CdS and CdSe layer depositions and the postdeposition CdCl2 treatment should be conducted in the presence of oxygen, the CdTe deposition should be conducted in an oxygen-free atmosphere. Improper oxygen management leads to low device performance due to the formation of a photoinactive Cd(S,Se) region and reduced absorber quality. Additionally, we investigated the carrier transport and collection properties in devices with photoinactive Cd(S,Se) and photoactive Cd(O,S,Se,Te) at the front interface to gain comprehensive understanding of the mechanisms that resulted in improved efficiencies approaching 20%.

CdTe deposition↗
DOE OSTI2021

Evolution of non-Kramers doublets in magnetic field in PrNi 2 Cd 20 and PrPd 2 Cd 20

Praseodymium-based 1-2-20 cage compounds PrT 2 X 20 (T is generally Ti, V, Nb, Ru, Rh, Ir; and X is either Al, Zn, or Cd) provide yet another platform to study nontrivial electronic states of matter ranging from topological and magnetic orders to unconventional multipolar orders and superconductivity. In this paper, we report measurements of the electronic heat capacity in two Pr-based 1-2-20 materials: PrNi 2 Cd 20 and PrPd 2 Cd 20 . We find that the lowest-energy multiplet of the Pr 4f 2 valence configuration is a Γ 3 non-Kramers doublet and the first excited triplet is assumed to be a magnetic Γ 5 . By analyzing the dependence of the energy splitting between the ground and first excited singlet states on an external magnetic field, we found that the maximum in the heat capacity corresponding to the Schottky anomaly in PrPd 2 Cd 20 , unlike PrNi 2 Cd 20 , shows a pronounced linear dependence on an external magnetic field at higher field values. In conclusion, this effect is associated with the exchange interactions between the field-induced magnetic dipole moments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Analysis of the rotationally-resolved infrared spectrum of CD 3 79 Br and CD 3 81 Br between 900 and 1400 cm -1

We report the infrared spectrum of CD 3 79 Br and CD 3 81 Br between 900 cm -1 and 1400 cm -1 has been analyzed at high resolution. In this region, two fundamental vibrational states, v 2 = 1 and v 5 = 1, an overtone state, v 3 = 2, and a combination state, v 3 = v 6 = 1, have been analyzed for both isotopologues. As found in other halomethane molecules, strong Coriolis resonances couple the v 2 = 1 state to the v 5 = 1 state, and similar resonances were also used to describe the coupling found between the v 5 = 1 state to the v 3 = 2 state. A new determination of the K-dependent constant A 0 was performed for each isotopologue through the use of perturbation-allowed transitions. The values for A 0 determined from the analysis are 2.6001898(26) and 2.6001905(27) for CD 3 79 Br and CD 3 81 Br, respectively. Ab initio calculations were performed to examine the efficacy of high-level theoretical calculations to accurately predict spectroscopic constants. The ab initio calculations had variable success with the largest errors associated with the prediction of the ΔB rotational constants of the interacting states

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1988

Phase diagrams and microscopic structures of (Hg,Cd)Te, (Hg,Zn)Te, and (Cd,Zn)Te alloys

A cluster theory based on the quasi-chemical approximation has been applied to study the local correlation bond-length distribution, and phase diagrams of the II-VI pseudobinary alloys Hg(1 - x)Cd(x)Te, Hg(1 - x)Zn(x)Te, and Cd(1 - x)Zn(x)Te. The cluster energy is calculated by letting it relax in some effective alloy medium and then considering the contributions from the strain and chemical energies. Two different models are presented to simulate the alloy medium. While both models show that all three alloys have nearly random distributions, the signs of the local correlation prove to be sensitive to the alloy medium chosen for the energy calculation. Good agreement is found between experiment and the bond lengths and phase diagrams in both models.

Patrick, R. S.↗
DOE OSTI2025

Multimodal characterization of Te inclusions in Cd 1−x Zn x Te and Cd 1−x Zn x Te 1−y Se y for gamma and X-ray detectors

While CdZnTe (CZT) and CdZnTeSe (CZTS) semiconductors have emerged as compounds for room-temperature gamma and X-ray detection materials, they continue to be constrained by the formation of Te-inclusion defects generated during the growth and post-growth phases of the material, which adversely affect the detector performance. We demonstrate the utility of multimodal microscopic imaging and analysis for the characterization of the optical and electronic properties of Te inclusions in CZT and CZTS crystals at both micron and nanometer length scales. Having first identified regions with micron-scale Te inclusions using confocal Raman microscopy techniques, optically coupled infrared scattering near-field optical microscopic mapping was performed to map the distribution of these inclusions with nanometer spatial resolution and correlate the presence of Te inclusions in the matrix with other properties. Kelvin probe force microscopy was then utilized to characterize the variations of the work function associated with the presence of Te inclusions. Here, we observe an increase of ~ 240 mV in the work function associated with Te inclusions compared to the bulk CZT/CZTS crystals. Additionally, we observe that individual bulk grains in CZT can exhibit slight potential variations. Our findings develop a portrait of the charge trapping mechanisms in CZT and CZTS that act to degrade detector performance, while the demonstration of these combined microscopy techniques provides a new analytical tool that can be utilized for further optimization of the detector performance for these semiconducting compounds.

36 MATERIALS SCIENCE↗
NASA NTRS1965

Cu-Cd and Ag-Cd cermet contacts

Method for preparing copper-cadmium and silver- cadmium cermet alloys without cadmium loss - evaluation of breaking electric contacts and collector plates

COLLECTOR↗
DOE OSTI2020

Materials Data on Cd(BrO2)2 by Materials Project

Cd(O2Br)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Cd sites. In the first Cd site, Cd is bonded to six O atoms to form distorted edge-sharing CdO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.34–2.38 Å. In the second Cd site, Cd is bonded to six O atoms to form distorted edge-sharing CdO6 octahedra. There are a spread of Cd–O bond distances ranging from 2.34–2.38 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Cd and one Br atom. The O–Br bond length is 1.75 Å. In the second O site, O is bonded in a bent 150 degrees geometry to one Cd and one Br atom. The O–Br bond length is 1.75 Å. In the third O site, O is bonded in a bent 150 degrees geometry to one Cd and one Br atom. The O–Br bond length is 1.75 Å. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Cd and one Br atom. The O–Br bond length is 1.75 Å. In the fifth O site, O is bonded in a trigonal non-coplanar geometry to two equivalent Cd and one Br atom. The O–Br bond length is 1.79 Å. In the sixth O site, O is bonded in a trigonal non-coplanar geometry to two equivalent Cd and one Br atom. The O–Br bond length is 1.79 Å. In the seventh O site, O is bonded in a trigonal non-coplanar geometry to two equivalent Cd and one Br atom. The O–Br bond length is 1.80 Å. In the eighth O site, O is bonded in a trigonal non-coplanar geometry to two equivalent Cd and one Br atom. The O–Br bond length is 1.80 Å. There are four inequivalent Br sites. In the first Br site, Br is bonded in a water-like geometry to two O atoms. In the second Br site, Br is bonded in a water-like geometry to two O atoms. In the third Br site, Br is bonded in a water-like geometry to two O atoms. In the fourth Br site, Br is bonded in a water-like geometry to two O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cd(BrO2)2 by Materials Project

Cd(O2Br)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Cd sites. In the first Cd site, Cd is bonded in a 4-coordinate geometry to four O atoms. There are a spread of Cd–O bond distances ranging from 2.24–2.38 Å. In the second Cd site, Cd is bonded in a 5-coordinate geometry to six O atoms. There are a spread of Cd–O bond distances ranging from 2.25–2.76 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a distorted trigonal non-coplanar geometry to one Cd and two Br atoms. There are one shorter (1.82 Å) and one longer (2.47 Å) O–Br bond lengths. In the second O site, O is bonded in a bent 120 degrees geometry to one Cd and one Br atom. The O–Br bond length is 1.79 Å. In the third O site, O is bonded in a bent 120 degrees geometry to one Cd and one Br atom. The O–Br bond length is 1.77 Å. In the fourth O site, O is bonded in a bent 120 degrees geometry to one Cd and one O atom. The O–O bond length is 1.26 Å. In the fifth O site, O is bonded in a bent 120 degrees geometry to one Cd and one O atom. In the sixth O site, O is bonded in a trigonal non-coplanar geometry to two equivalent Cd and one Br atom. The O–Br bond length is 1.85 Å. In the seventh O site, O is bonded in a trigonal planar geometry to two equivalent Cd and one Br atom. The O–Br bond length is 1.79 Å. In the eighth O site, O is bonded in a 3-coordinate geometry to one Cd and two Br atoms. There are one shorter (1.83 Å) and one longer (2.38 Å) O–Br bond lengths. There are four inequivalent Br sites. In the first Br site, Br is bonded in a water-like geometry to two O atoms. In the second Br site, Br is bonded in a distorted single-bond geometry to one O atom. In the third Br site, Br is bonded in a single-bond geometry to one O atom. In the fourth Br site, Br is bonded in a distorted rectangular see-saw-like geometry to four O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77 Se and 113 Cd Solid-State NMR Spectroscopy

Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D 113 Cd and 77 Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. 113 Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe 3 O, CdSe 2 O 2 , and CdSeO 3 Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear 113 Cd– 113 Cd and 77 Se– 77 Se and heteronuclear 113 Cd– 77 Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, 77 Se{ 113 Cd} scalar heteronuclear multiple quantum coherence ( J -HMQC) experiments were used to selectively measure one-bond 77 Se– 113 Cd scalar coupling constants ( 1 J ( 77 Se, 113 Cd)). With knowledge of 1 J ( 77 Se, 113 Cd), heteronuclear 77 Se{ 113 Cd} spin echo ( J -resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. Furthermore, the J -resolved experiments directly confirmed that major Cd and Se surface species have CdSe 2 O 2 and SeCd 4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Evaluation of 6-OxP-CD, an Oxime-based cyclodextrin as a viable medical countermeasure against nerve agent poisoning: Experimental and molecular dynamic simulation studies on its inclusion complexes with cyclosarin, soman and VX

The ability of the cyclodextrin-oxime construct 6-OxP-CD to bind and degrade the nerve agents Cyclosarin (GF), Soman (GD) and S -[2-[Di(propan-2-yl)amino]ethyl] O -ethyl methylphosphonothioate (VX) has been studied using 31 P-nuclear magnetic resonance (NMR) under physiological conditions. While 6-OxP-CD was found to degrade GF instantaneously under these conditions, it was found to form an inclusion complex with GD and significantly improve its degradation (t 1/2 ~ 2 hrs) relative over background (t 1/2 ~ 22 hrs). Consequently, effective formation of the 6-OxP-CD:GD inclusion complex results in the immediate neutralization of GD and thus preventing it from inhibiting its biological target. In contrast, NMR experiments did not find evidence for an inclusion complex between 6-OxP-CD and VX, and the agent’s degradation profile was identical to that of background degradation (t 1/2 ~ 24 hrs). As a complement to this experimental work, molecular dynamics (MD) simulations coupled with Molecular Mechanics-Generalized Born Surface Area (MM-GBSA) calculations have been applied to the study of inclusion complexes between 6-OxP-CD and the three nerve agents. These studies provide data that informs the understanding of the different degradative interactions exhibited by 6-OxP-CD with each nerve agent as it is introduced in the CD cavity in two different orientations (up and down). For its complex with GF, it was found that the oxime in 6-OxP-CD lies in very close proximity (P GF …O Oxime ~ 4–5 Å) to the phosphorus center of GF in the ‘down GF ’ orientation for most of the simulation accurately describing the ability of 6-OxP-CD to degrade this nerve agent rapidly and efficiently. Further computational studies involving the center of masses (COMs) for both components (GF and 6-OxP-CD) also provided some insight on the nature of this inclusion complex. Distances between the COMs (ΔCOM) lie closer in space in the ‘down GF ’ orientation than in the ‘up GF ’ orientation; a correlation that seems to hold true not only for GF but also for its congener, GD. In the case of GD, calculations for the ‘down GD ’ orientation showed that the oxime functional group in 6-OxP-CD although lying in close proximity (P GD …O Oxime ~ 4–5 Å) to the phosphorus center of the nerve agent for most of the simulation, adopts another stable conformation that increase this distance to ~ 12–14 Å, thus explaining the ability of 6-OxP-CD to bind and degrade GD but with less efficiency as observed experimentally (t 1/2 ~ 4 hr. vs. immediate). Lastly, studies on the VX:6-OxP-CD system demonstrated that VX does not form a stable inclusion complex with the oxime-bearing cyclodextrin and as such does not interact in a way that is conducive to an accelerated degradation scenario. Collectively, these studies serve as a basic platform from which the development of new cyclodextrin scaffolds based on 6-OxP-CD can be designed in the development of medical countermeasures against these highly toxic chemical warfare agents.

60 APPLIED LIFE SCIENCES↗