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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 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility

We report that ternary metal oxides of type (Me) 2 O 3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 10 4 S/m) and Hall mobility (>30 cm 2 /V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV. This material shows emergent semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. In conclusion, since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Stabilization of Si microwire arrays for solar-driven H 2 O oxidation to O 2 (g) in 1.0 M KOH(aq) using conformal coatings of amorphous TiO 2

In this work, conductive, amorphous TiO 2 coatings deposited by atomic-layer deposition, in combination with a sputter deposited NiCrO x oxygen-evolution catalyst, have been used to protect Si microwire arrays from passivation or corrosion in contact with aqueous electrolytes. Coated np + -Si/TiO 2 /NiCrO x as well as heterojunction n-Si/TiO 2 /NiCrO x Si microwire-array photoanodes exhibited stable photoelectrochemical operation in aqueous ferri-/ferro-cyanide solutions. The coatings also allowed for photoanodic water oxidation in 1.0 M KOH(aq) solutions for >2200 h of continuous operation under simulated 1 Sun conditions with ~100% Faradaic efficiency for the evolution of O 2 (g).

Shaner, Matthew R.↗
DOE OSTI2014

Chemical Bonding In Amorphous Si Coated-carbon Nanotube As Anodes For Li ion Batteries: A XANES Study

The chemical bonding nature and its evolution upon electrochemical cycling in amorphous Si coated-carbon nanotube (Si-CNT) anode has been investigated using comprehensive X-ray absorption spectroscopy (XANES) at Si L- and K-edges along with C and O K-edges. The Si nanolayer on CNT is found to be anchored to CNT via Si-O-C bonding. This bond weakens upon electrochemical cycling accompanied with generation of Li2CO3 on the surface of Si-CNT. Those findings are crucial in designing further improved Si-C composite anode for lithium ion battery.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III–V light absorbers protected by amorphous TiO 2 films

A monolithically integrated device consisting of a tandem-junction GaAs/InGaP photoanode coated by an amorphous TiO 2 stabilization layer, in conjunction with Ni-based, earth-abundant active electrocatalysts for the hydrogen-evolution and oxygen-evolution reactions, was used to effect unassisted, solar-driven water splitting in 1.0 M KOH(aq). When connected to a Ni–Mo-coated counterelectrode in a two-electrode cell configuration, the TiO 2 -protected III–V tandem device exhibited a solar-to-hydrogen conversion efficiency, η STH , of 10.5% under 1 sun illumination, with stable performance for >40 h of continuous operation at an efficiency of η STH > 10%. The protected tandem device also formed the basis for a monolithically integrated, intrinsically safe solar-hydrogen prototype system (1 cm 2 ) driven by a NiMo/GaAs/InGaP/TiO 2 /Ni structure. The intrinsically safe system exhibited a hydrogen production rate of 0.81 μL s –1 and a solar-to-hydrogen conversion efficiency of 8.6% under 1 sun illumination in 1.0 M KOH(aq), with minimal product gas crossover while allowing for beneficial collection of separate streams of H 2 (g) and O 2 (g).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Electronic and optical properties of oxygen vacancies in amorphous Ta 2 O 5 from first principles

Oxygen vacancies are important defects considered to play a central role in the electronic and optical properties of tantalum pentoxide (Ta2O5) films and devices. Despite extensive experimental studies on oxygen vacancies in Ta2O5, the reported defect states are ambiguously identified due to the absence of accurate and conclusive theoretical evidence. Here we investigate the thermodynamic, electronic, and optical properties of oxygen vacancies in amorphous Ta2O5 by first-principles calculations based on hybrid-functional density functional theory (DFT). The calculated thermodynamic and optical transition levels are in good agreement with a broad range of diverse measured properties with various experimental methods, providing conclusive evidence for the identification of the defect states observed in experiments as originating from oxygen vacancies. Our calculations also predict the formation of spin-polarized polarons. Our results elucidate the fundamental atomistic properties of oxygen vacancies in various oxidation states as a function of growth conditions and provide guidance to control the properties of Ta2O5 films/devices.

Lee, Jihang↗
DOE OSTI2018

Growth of amorphous and epitaxial ZnSiP 2 –Si alloys on Si

ZnSiP 2 is a wide band gap material lattice matched with Si, with potential for Si-based optoelectronics. Here, amorphous ZnSiP 2 –Si alloys are grown with tunable composition. Films with Si-rich compositions can be crystallized into epitaxial films.

14 SOLAR ENERGY↗
DOE OSTI2018

Electrokinetic flow of an aqueous electrolyte in amorphous silica nanotubes

Here, we study the pressure-driven flow of aqueous NaCl in amorphous silica nanotubes using nonequilibrium molecular dynamics simulations featuring both polarizable and non-polarizable molecular models. Different pressures, electrolyte concentrations and pore sizes are examined. Our results indicate a flow that deviates considerably from the predictions of Poiseuille fluid mechanics. Due to preferential adsorption of the different ionic species by surface SiO– or SiOH groups, we find that a significant electric current is generated, but with opposite polarities using polarizable vs. fixed charge models for water and ions, emphasizing the need for careful parameterization in such complex systems. We also examine the influence of partial deprotonation of the silica surface, and we find that much more current is generated in a dehydrogenated nanopore, even though the overall efficiency remains low. These findings indicate that different methods of nanopore preparation, which can produce a range of surface properties, should be examined more closely in the related experimental methods to generate electrokinetic current.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Crystallization kinetics of amorphous calcium carbonate in confinement

In situ observation of amorphous calcium carbonate (ACC) confined in ~500 pL emulsion droplets allows determination of the timing of individual crystal nucleation events. Statistical analysis of events in hundreds of droplets establishes an upper limit for the steady-state nucleation rate of 1.2 cm -3 s -1 for the crystallization from ACC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Molecular Blends of Methylated-Poly(ethylenimine) and Amorphous Porous Organic Cages for SO 2 Adsorption

Porous organic cages (POCs) are emerging porous materials that exhibit intriguing properties in the areas of self-assembly, host-guest interaction, and solution processability. Here in this work, we explore the applicability of POCs as molecular porous supports for polymeric amines. We find that primary amines in poly(ethylenimine) (PEI) can undergo metathesis with the imine bonds present in POCs, resulting in non-porous products. This problem can be overcome by transforming the primary amines in PEI to tertiary amines via methylation. The methylated PEI (mPEI) forms homogeneous composites with amorphous scrambled porous organic cages (ASPOCs) without undesired reactions or phase separation. The microscopic structure of the composites is studied using molecular dynamics simulations. Finally, these composite materials are evaluated as adsorbents for low concentration SO2 (200 ppm) adsorption and show good thermal and cyclic stability.

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

Low temperature and limited water activity reveal a pathway to magnesite via amorphous magnesium carbonate

Forsterite carbonated in thin H 2 O films to magnesite via amorphous magnesium carbonate during reaction with H 2 O-bearing liquid CO 2 at 25 °C. This novel reaction pathway contrasts with previous studies that were carried out at higher H 2 O activity and temperature, where more highly hydrated nesquehonite was the metastable intermediate.

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

Structural evolution of amorphous calcium sulfate nanoparticles into crystalline gypsum phase

The involvement of amorphous calcium sulfate (ACS) as a precursor to calcium sulfate crystallization remains an important but poorly understood phenomenon, especially the mechanism by which ACS evolves into crystalline phase. In this study, we captured the ACS nanoparticles as a precursor to calcium sulfate crystallization in a concentrated CaCl 2 solution at 90 °C and observed several stages of its evolution. The ACS nanoparticles grew by simultaneous fusion and internal structural evolution. Aggregation of the ACS nanoparticles gave birth to bulk ACS particles within which nanocrystalline domains sprouted and developed into crystalline gypsum. This work deepens the understanding of the evolution of ACS nanoparticles and its role in multistage crystallization of calcium sulfate.

36 MATERIALS SCIENCE↗