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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 OSTI2022

First-principles ionized-impurity scattering and charge transport in doped materials

Scattering of carriers with ionized impurities governs charge transport in doped semiconductors. However, electron interactions with ionized impurities cannot be fully described with quantitative first-principles calculations, so their understanding relies primarily on simplified models. Here we show an ab initio approach to compute the interactions between electrons and ionized impurities or other charged defects. It includes the short- and long-range electron-defect (e-d) interactions on equal footing and allows for efficient interpolation of the e-d matrix elements. Here we combine the e-d and electron-phonon interactions in the Boltzmann transport equation to compute the carrier mobilities in doped silicon over a wide range of temperature and doping concentrations, seamlessly spanning the defect- and phonon-limited transport regimes. The individual contributions of the defect- and phonon-scattering mechanisms to the carrier relaxation times and mean-free paths are analyzed. Our method provides a powerful tool to study electronic interactions in doped materials. It broadens the scope of first-principles transport calculations, enabling studies of a wide range of doped semiconductors and oxides with application to electronics, energy, and quantum technologies.

36 MATERIALS SCIENCE↗
NASA NTRS2018

Mid-infrared Spectroscopy of Pr-Doped Materials

Solid state lanthanide doped lasers primarily operate in the ultraviolet, visible, near infrared and short-wavelength infrared out to around 2.1 μm. At longer wavelengths, the transitions in conventional oxide crystal and glass materials become susceptible to multiphonon quenching due to their relatively large phonon energy. The use of low phonon materials can minimize the nonradiative quenching, opening up possibilities for solid state lanthanide lasers operating in the mid-infrared (MIR). This provides motivation to study the spectroscopy of lanthanide ions in bromide, chloride and fluoride materials, which have relatively low phonon energies. In this article, the MIR spectroscopy or praseodymium ions in five different host materials is studied, specifically KPb2Br5 (KPB), LaF3, KYF4 (KYF), BaY2F8 (BYF) and YLiF4 (YLF) host crystals. The MIR emission cross sections have been measured from 3 to 6 μm and reciprocity of absorption and emission is utilized to validate the results. The lifetime dynamics in the MIR are covered for various pump and emission wavelengths. Results are also presented on MIR emission from 6.5 to 8.5 μm in a Pr: KPB crystal, which, to the best of the authors knowledge, is the first such measurement of luminescence in this wavelength range that has been published.

Brian M Walsh↗
DOE OSTI2020

De novo fabrication of multi-heteroatom-doped carbonaceous materials via an in situ doping strategy

Finding a succinct strategy to fabricate multi-heteroatom-doped nanoporous carbonaceous materials is a long-term challenge and highly desired research topic. The key to success is the rational design of easy to obtain and functionalized precursors. Herein, de novo fabrication of carbonaceous materials doped with multiple heteroatoms namely boron, nitrogen, oxygen, fluorine, and sulfur was achieved via a one-step in situ doping procedure using task-specific ionic liquids (TSILs) as precursors. Our strategy hinges on the adoption of particularly designed TSILs with structures functionalized with (1) boron source-containing anions, (2) imidazolium functionalities as the carbon and nitrogen source, (3) nitrile groups capable of trimerization during the heating process, and (4) bis(trifluoromethanesulphonyl)imide and related anions performing as the source of heteroatoms (i.e., fluorine, nitrogen, sulfur, and oxygen) and porogens. The unique structures of the as-prepared TSILs make them qualified precursors for the production of multi-heteroatom-doped carbonaceous materials through simple thermal treatment, with surface areas up to 1021 m 2 g -1 . The introduction of multiple heteroatoms provides the carbonaceous materials with efficient adsorption performance for the capture of hazardous anionic pollutants, dyes, and neutral organic molecules. This finding expands the versatility of TSILs with multi-functionalized architectures, delivering nanoporous materials with wide applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nonstoichiometric Salt Intercalation as a Means to Stabilize Alkali Doping of 2D Materials

Although doping with alkali atoms is a powerful technique for introducing charge carriers into physical systems, the resulting charge-transfer systems are generally not air stable. Here, in this paper, we describe computationally a strategy towards increasing the stability of alkali-doped materials that employs stoichiometrically unbalanced salt crystals with excess cations (which could be deposited during, e.g., in situ gating) to achieve doping levels similar to those attained by pure alkali metal doping. The crystalline interior of the salt crystal acts as a template to stabilize the excess dopant atoms against oxidation and deintercalation, which otherwise would be highly favorable. We characterize this doping method for graphene, NbSe 2 , and Bi 2 Se 3 and its effect on direct-to-indirect band gap transitions, 2D superconductivity, and thermoelectric performance. Salt intercalation should be generally applicable to systems which can accommodate this “ionic crystal” doping (and particularly favorable when geometrical packing constraints favor nonstoichiometry).

2-dimensional systems↗
NASA NTRS1971

Doping explosive materials for neutron radiographic enhancement.

Discussion of studies relating to the selection of doping materials of high neutron absorption usable for enhancing the neutron radiographic imaging of explosive mixtures, without interfering with the proper chemical reaction of the explosives. The results of the studies show that gadolinium oxide is an excellent material for doping explosive mixtures to enhance the neutron radiographic image.

Golliher, K. G.↗
NASA NTRS1993

Synthesis of phthalocyanine doped sol-gel materials

The synthesis of sol-gel silica materials doped with three different types of metallophthalocyanines has been studied. Homogeneous materials of good optical quality were prepared and the first optical limiting measurements of dyes in sol-gel hosts were carried out. The properties of these solid state limiters are similar to limiters based on phthalocyanine (Pc) in solution. Sol-gel silica materials containing copper, tin and germanium phthalocyanines were investigated. The initial step in all cases was to prepare silica sols by the sonogel method using tetramethoxy silane (TMOS), HCl and distilled water. Thereafter, the synthesis depended upon the specific Pc and its solubility characteristics. Copper phthalocyanine tetrasulfonic acid tetra sodium salt (CuPc4S) is soluble in water and various doping levels (1 x 10 (exp -4) M to 1 x 10 (exp -5) M) were added to the sol. The group IV Pc's, SnPc(OSi(n-hexyl)3)2 and GePc(OSi(n-hexyl)3)2, are insoluble in water and the process was changed accordingly. In these cases, the compounds were dissolved in THF and then added to the sol. The Pc concentration in the sol was 2 x 10(exp -5)M. The samples were then aged and dried in the standard method of making xerogel monoliths. Comparative nanosecond optical limiting experiments were performed on silica xerogels that were doped with the different metallophthalocyanines. The ratio of the net excited state absorption cross section (sigma(sub e)) to the ground state cross section (sigma(sub g)) is an important figure of merit that is used to characterize these materials. By this standard the SnPc sample exhibits the best limiting for the Pc doped sol-gel materials. Its cross section ratio of 19 compares favorably with the value of 22 that was measured in toluene. The GePc materials appear to not be as useful as those containing SnPc. The GePc doped solids exhibit a higher onset energy (2.5 mj and lower cross section ratio, 7. The CuPc4S sol-gel material has a still lower cross section ratio, 4, however, the tetrasulfonate groups make the dye soluble in water which greatly facilitates its incorporation into the sol-gel matrix. The nonlinear transmission of CuPc4S in a pH 2 buffer solution and in a silica xerogel were compared. It is evident that the CuPc4S preserves its optical limiting behavior in the sol-gel matrix, indicating that the fundamental excited state absorption process is essentially the same for a molecule in solution or in the solid state. Although the spectroscopic details of energy level lifetimes are unknown, the significance is that passive optical limiting has been achieved in the solid state via incorporation of a dye into an inorganic host. The only compromise occurs at the extremely high energy regime where photobleaching is observed. This is a result of the limited mobility of the dye molecules in the solid silica host relative to a liquid host. The effects of photodegradation in the xerogel are additive, whereas the solution provides a supply of fresh molecules that are free to enter the active volume between pulses.

Dunn, Bruce↗
DOE OSTI2020

Controlled Dy-doping to nickel-rich cathode materials in high temperature aerosol synthesis

Layered nickel-rich materials are promising next-generation cathode materials for lithium ion batteries due to their high capacity and low cost. However, the poor thermal stability and longtime cycling performance hinders the commercial applications of high nickel materials. Doping with heteroatoms has been an effective approach for improving electrochemical performance of cathode materials. Controlling doping concentration and geometrical distribution is desired for optimal electrochemical performance, but it is challenging in traditional co-precipitation methods. In this work, controlled dysprosium (Dy) doping to NCM811 was studied in an aerosol synthesis method by controlling the precursor concentrations and heating parameters. The obtained materials were characterized by SEM, XRD, and XPS, and their electrochemical properties and thermal stability were evaluated. By controlling the doping concentration (1.5%), Dy-doped NCM811 was improved simultaneously in long-term cycling and high-rate performance. Here, the thermal-chemical stability of the Dy-doped cathode materials was examined in a microflow reactor with a mass spectrometer. The results showed that Dy-doping shifted the O 2 onset temperature to a higher temperature and reduced O 2 release by 80%, thus dramatically increasing the thermal-chemical stability and improving the fire safety of cathode materials. Since high temperature aerosol synthesis is a low-cost and scalable method, the findings in this work have broad implications for commercial synthesis of novel materials with controlled doping modification to achieve high electrochemical performance and safety in lithium ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

The impact of 2 H 9/2 → 4 I 13/2 emission from Er 3+ ions on ratiometric optical temperature sensing with Yb 3+ /Er 3+ co-doped upconversion materials

Yb 3+ /Er 3+ co-doped upconversion materials are widely used for luminescence intensity ratio (LIR) thermometry, where the relative intensity ratio of the green luminescence transitions ( 2 H 11/2 4 I 15/2 and 4 S 3/2 4 I 15/2 ) of Er 3+ dopant ions changes with temperature. In this work we report on the impact of an additional transition from the 2 H 9/2 level to the intermediate 4 I 13/2 level, which overlaps with the green luminescence normally used for LIR thermometry. The 2 H 9/2 4 I 13/2 emission overlaps extensively with the 4 S 3/2 4 I 15/2 emission and is more sensitive to pump power. The wavelength intervals used to integrate both 2 H 11/2 4 I 15/2 and 4 S 3/2 4 I 15/2 luminescence need be selected carefully in order to achieve accurate temperature readouts.

36 MATERIALS SCIENCE↗
NASA NTRS1971

Radiation tolerance of aluminum-doped silicon

Data are presented that indicate that heat-treated Czochralski-grown aluminum doped silicon that undergoes an appreciable resistivity increase during heating at approximately 450 C is significantly more resistant to both neutron and gamma irradiation than boron doped material (or aluminum doped material that either has not been heat treated or does not experience an appreciable resistivity change during such a treatment). Data interpretation is, however, quite difficult due to the occurrence of severe trapping effects in heat treated material.

Curtis, O. L., Jr.↗
DOE OSTI2020

Identification of Active Sites of Pure and Nitrogen-Doped Carbon Materials for Oxygen Reduction Reaction Using Constant-Potential Calculations

Nitrogen-doped carbon materials are promising metal-free catalysts for the electrochemical oxygen reduction reaction (ORR). A better theoretical understanding on the nature of the active site(s) would help further optimization of their ORR activity. Although quantum mechanical calculations have been widely employed to elucidate the active sites over various catalysts, these calculations are typically done assuming constantcharge conditions rather than the experimentally relevant constant-potential conditions. In this study, we employ the double-reference method to simulate the energetics of the ORR over pure and N-doped carbon materials under constant-potential conditions. We demonstrate that constant-potential calculations enable more accurate theoretical predictions, comparing well with existing experiments. Our key findings are (1) the zigzag edge of pure graphite is highly active for ORR, (2) the pyridinic N-doped armchair edge is highly active for ORR in alkaline media but not in acid, and (3) graphitic N can donate electrons to pyridinic N to enhance the ORR activity. Furthermore, these fundamental insights provide guidelines for the design of better carbonbased ORR catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2008

Tetravalent chromium doped laser materials and NIR tunable lasers

A method is described to improve and produce purer Cr.sup.4+-doped laser materials and lasers with reduced co-incorporation of chromium in any other valence states, such as Cr.sup.3+, Cr.sup.2+, Cr.sup.5+, and Cr.sup.6+. The method includes: 1) certain crystals of olivine structure with large cation (Ca) in octahedral sites such as Cr.sup.4+:Ca.sub.2GeO.sub.4, Cr.sup.4+:Ca.sub.2SiO.sub.4, Cr.sup.4+:Ca.sub.2Ge.sub.xSi.sub.1-xO.sub.4 (where 0<x<1), and/or 2) high-temperature solution growth techniques that enable the growth of the crystals below the temperature of polymorphic transitions by using low melting point solvent based on oxide, fluoride and/or chloride compounds. Purer Cr.sup.4+-doped laser materials are characterized by a relatively high concentration of Cr.sup.4+-lasing ion in crystalline host that makes these materials suitable for compact high power (thin disk/wedge) NIR laser applications.

Alfano, Robert R.↗
NASA NTRS1986

Si3N4-Based Ceramic With Greater Hot Strength

Zyttrite-doped material outperforms MgO-doped material above 1,200 degrees C. New ceramic material produced by addition of 10 weight percent zyttrite (yttria-stabilized zirconia) to (silicon nitride) offers significantly-improved high-temperature properties (those of MgO-doped Si3N4 ceramic). Work also showed that controlled Si3N4 powder with 10 weight percent zyttrite, significant improvement in room-temperature strength achieved. Variety of high-temperature structural applications are silicon nitride and silicon carbide. Potential for use in aircraft and automobile engines and in electric-power generating systems. Improved properties strongly suggest that the 10-weight percent zyttrite/Si3N4 material has strong potential for high-temperature applications.

Dutta, S.↗
DOE OSTI2024

High-temperature thermochemical energy storage materials using doped magnesium-transition metal spinel oxides

High-temperature thermochemical energy storage materials using doped magnesium-transition metal spinel oxides are provided. —transition metal spinel oxides, such as magnesium manganese oxide (MgMn) 3 O 4 , are promising candidates for high-temperature thermochemical energy storage applications. However, the use of these materials has been constrained by the limited extent of their endothermic reaction. Embodiments described herein provide for doping magnesium-transition metal spinel oxides to produce a material of low material costs and with high energy densities, creating an avenue for plausibly sized modules with high energy storing capacities.

Muhich, Christopher↗
NASA NTRS2005

Study of Electromagnetic Scattering From Material Object Doped Randomly With Thin Metallic Wires Using Finite Element Method

A new numerical simulation method using the finite element methodology (FEM) is presented to study electromagnetic scattering due to an arbitrarily shaped material body doped randomly with thin and short metallic wires. The FEM approach described in many standard text books is appropriately modified to account for the presence of thin and short metallic wires distributed randomly inside an arbitrarily shaped material body. Using this modified FEM approach, the electromagnetic scattering due to cylindrical, spherical material body doped randomly with thin metallic wires is studied.

Deshpande, Manohar D.↗
DOE OSTI2022

Erbium-implanted materials for quantum communication applications

Erbium-doped materials can serve as spin-photon interfaces with optical transitions in the telecom C band, making them an exciting class of materials for long-distance quantum communication. However, the spin and optical coherence times of Er 3+ ions are limited by currently available host materials, motivating the development of new Er 3+ -containing materials. Here we demonstrate the use of ion implantation to efficiently screen prospective host candidates, and show that disorder introduced by ion implantation can be mitigated through post-implantation thermal processing to achieve inhomogeneous linewidths comparable to bulk linewidths in as-grown samples. We present optical spectroscopy data for each host material, which allows us to determine the level structure of each site, allowing us to compare the environments of Er 3+ introduced via implantation and via doping during growth. Here, we demonstrate that implantation can generate a range of local environments for Er 3+ , including those observed in bulk-doped materials, and that the populations of these sites can be controlled with thermal processing.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Controlling N speciation in solution synthesis of N-doped carbon materials

Carbon-based materials, such as graphite and its functionalized/doped derivatives, are promising lightweight layered materials for hydrogen activation and storage. Their propensity to control the thermodynamics of hydrogen binding and the kinetics of hydrogen mobility strongly depends on the speciation and the arrangement of dopants. In this study, we demonstrate precise control over dopant speciation and clustering in nitrogen-containing layered carbon materials during hydrothermal synthesis. Through extensive spectroscopic characterization and first principles simulations, we demonstrate that the formation of N-motifs can be controlled by the choice of precursor and synthesis temperature. The distinct three-dimensional architecture and porosity in graphene oxide and carbon nitride-derived materials furnish a synthetic pathway for precise control over the local and global structure of nitrogen-doped carbon materials and their activity toward the activation of molecular hydrogen.

Byun, Mi Yeon [Pacific Northwest National Laborato↗