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Results for “Polycrystalline structure”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Microstructure-dependent rate theory model of defect segregation and phase stability in irradiated polycrystalline LiAlO 2

We report gamma lithium aluminate (LiAlO 2 ) is a breeder material for tritium and is one of key components in a tritium-producing burnable absorber rod (TPBAR). Dissolution and precipitation of second phases such as LiAl 5 O 8 and voids are observed in irradiated LiAlO 2 . Such microstructure changes cause the degradation of thermomechanical properties of LiAlO 2 and affect tritium retention and release kinetics, and hence, the TPBAR performance. In this work, a microstructure-dependent model of radiation-induced segregation (RIS) has been developed for investigating the accumulation of species and phase stability in polycrystalline LiAlO 2 structures under irradiation. Three sublattices (i.e. [Li, Al, V] I [O, V o ] II [Li i , Al i , O i , V i ] III ), and concentrations of six diffusive species (i.e. Li; vacancy of Li or Al at [Li, Al, V] I sublattice, O vacancy at [O, V o ] II sublattice, and Li, Al and O interstitials at [Li i , Al i , O i , V i ] III interstitial sublattices; are used to describe spatial and temporal distributions of defects and chemistry. Microstructure-dependent thermodynamic and kinetic properties including the generation, reaction, and chemical potentials of defects and defect mobility are taken into account in the model. The parametric studies demonstrated the capability of the developed RIS model to assess the effect of thermodynamic and kinetic properties of defects on the segregation and depletion of species in polycrystalline structures and to explain the phase stability observed in irradiated LiAlO 2 samples. The developed RIS model will be extended to study the precipitation of LiAl 5 O 8 and voids and tritium retention by integrating the phase-field method.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Formation and evolution of tweed structures on high-purity aluminum polycrystalline foils under cyclic tension

Peculiarities of formation and evolution of tweed structures on the surface of high-purity aluminum polycrystalline foils under cyclic tension were studied using an atom force microscope and a white light interferometer. Tweed structures of micron and submicron sizes were found on the foils at different number of cycles. In the range of 42,000 < N < 95,000 cycles destruction of tweed patterns is observed, which leads to their disappearance from the surface of the foils. Formation of tweed structures of various scales is discussed in terms of the Grinfeld instability.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Starch-assisted synthesis and optical properties of ZnS nanoparticles

Highlights: • ZnS spherical nanostructure was prepared via starch-assisted method. • The crystalline lattice structure, morphologies, chemical and optical properties of ZnS nanoparticles. • The forming mechanism of ZnS nanoparticles. • ZnS spherical nano-structure can show blue emission at 460–500 nm. - Abstract: ZnS nanoparticles are fabricated via starch-assisted method. The effects of different starch amounts on structure and properties of samples are investigated, and the forming mechanism of ZnS nanoparticles is discussed. By X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–vis) spectroscopy and fluorescence (FL) spectrometer, their phases, crystalline lattice structure, morphologies, chemical and optical properties are characterized. The results show that ZnS has polycrystalline spherical structure with the mean diameter of 130 nm. Sample without starch reveals irregular aggregates with particle size distribution of 0.5–2 μm. The band gap value of ZnS is 3.97 eV. The chemical interaction exists between starch molecules and ZnS nanoparticles by hydrogen bonds. The stronger FL emission peaks of ZnS synthesized with starch, indicate a larger content of sulfur vacancies or defects than ZnS synthesized without starch.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Formation of ZnO Nanocrystalline via Facile Non-Hydrolytic Route

Zinc oxide (ZnO) nanocrystalline were synthesized via oxidizing Zn powder in non-aqueous solvent with addition of Diethanolamine (DEA) as a stabilizing agent. The influence of DEA on the structural, optical properties and the formation of ZnO nanocrystalline were studied. The synthesized ZnO were polycrystalline in structures where sample without the addition of DEA shows high intensity peak of (002) phase compared with sample in the presence of DEA which preferred to grow in (101) direction. SEM micrograph displays the morphology of ZnO nanocrystalline for both of the samples which shows micron size and non-uniform particles for sample without DEA whereas for sample with DEA exhibit smaller size ({approx}110 nm) and nearly spherical in shape despite of some agglomeration occurs at the interparticle separation. The photoluminescence (PL) spectra shows UV emission peak for both of the samples where sample with the absence of DEA possess lower intensity of UV emission peak compared to samples with DEA which demonstrate stronger intensity despite of having very weak visible secondary emission peak at 530 nm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Weak ferromagnetic ordering in Ca doped polycrystalline BiFeO{sub 3}

Structural and magnetic properties of polycrystalline BiFeO{sub 3}, Bi{sub 0.9}Ca{sub 0.1}FeO{sub 2.95}, Bi{sub 0.9}Ba{sub 0.05}Ca{sub 0.05}FeO{sub 2.95}, and Bi{sub 0.9}Ba{sub 0.1}FeO{sub 2.95} ceramic samples were studied to establish the effects of doping in BiFeO{sub 3} on the magnetic property. X-ray diffraction data of the undoped and doped BiFeO{sub 3} samples were refined to a rhombohedral structure with space group R3c. X-ray photoelectron spectroscopy study showed the formation of a single-phase in both the undoped and doped BiFeO{sub 3} ceramics with Fe in the 3+ valence state. Ca doped and Ba-Ca co-doped BiFeO{sub 3} ceramic samples show weak ferromagnetic ordering at room temperature. This observation makes Ca doped and Ba-Ca co-doped BiFeO{sub 3} samples an interesting material system for magnetoelectric coupling studies.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Graph-component approach to defect identification in large atomistic simulations

In this work, the graph-theoretical concept of connected components is employed to extract the evolution of defect configurations in a polycrystalline aluminum structure containing ~8.3 million atoms. This graph-component approach is applied to reveal details of defect formation, transport, and transformation in the polycrystalline Al under large shear deformation. Building upon standard nearest neighbor analysis, graph theory and associated tools are used to reduce the multi-million-atom system into discrete component subgraphs that represent distinct structural defects. This method allows the automated identification, characterization, and tracking of defective regions within large volumes of data representing atomic-scale processes. Such analysis elucidates relationships between external stimuli, such as strain, and defect distributions, which have a large influence on material properties. The Graph Analytics for Large Atomistic Simulations (GALAS) codebase that implements this analysis, together with user guidance, is openly available at https://github.com/pnnl/galas.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Platinum-induced structural collapse in layered oxide polycrystalline films

Effect of a platinum bottom electrode on the SrBi{sub 5}Fe{sub 1−x}Co{sub x}Ti{sub 4}O{sub 18} layered oxide polycrystalline films was systematically studied. The doped cobalt ions react with the platinum to form a secondary phase of PtCoO{sub 2}, which has a typical Delafossite structure with a weak antiferromagnetism and an exceptionally high in-plane electrical conductivity. Formation of PtCoO{sub 2} at the interface partially consumes the cobalt dopant and leads to the structural collapsing from 5 to 4 layers, which was confirmed by X-ray diffraction and high resolution transmission electron microscopy measurements. Considering the weak magnetic contribution from PtCoO{sub 2}, the observed ferromagnetism should be intrinsic of the Aurivillius compounds. Ferroelectric properties were also indicated by the piezoresponse force microscopy. In this work, the platinum induced secondary phase at the interface was observed, which has a strong impact on Aurivillius structural configuration and thus the ferromagnetic and ferroelectric properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Nd3+ Doping effect on the optical and electrical properties of SnO2 thin films prepared by nebulizer spray pyrolysis for opto-electronic application

Highlights: • High quality, Nd:SnO{sub 2} thin films prepared using simple nebulizer spray pyrolysis technique. • Characterizations of the films confirmed good crystallinity and smooth surface morphology. • High optical transparency with low electrical resistivity in nebulizer spray pyrolysis prepared Nd: SnO{sub 2} thin films is presented. - Abstract: Neodymium doped tin oxide (Nd: SnO{sub 2}) thin films were deposited on heated glass substrates with different Nd concentrations (0, 2, 4 and 6 %) by nebulizer spray pyrolysis method. Effects of Nd doping on structural, optical and electrical properties of the prepared films were investigated. X-ray diffraction study confirmed that all the deposited Nd: SnO{sub 2} films are in polycrystalline tetragonal structure with (211) preferential orientation. FESEM images showed that the prepared SnO{sub 2} particles are in nano-size in spherical shape, completely covering the substrate. AFM topology showed smooth deposition of the films with minimum surface roughness. The films showed maximum optical transmittance 90 % in the visible region with a band gap value 3.67 eV, also showed low refractive index and extinction coefficients. Room temperature photoluminescence (PL) spectrum exhibited a strong UV emission peak at 356 nm for all the films. All the Nd: SnO{sub 2} films displayed n-type conductivity with low electrical resistivity 5.88 × 10{sup −4} (Ω cm) for 4 % Nd doping. As the films showed good figure of merit (ϕ) values, these Nd doped SnO{sub 2} thin films can perform better role in optoelectronic device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural, optical, and magnetic properties of Fe doped In{sub 2}O{sub 3} powders

Highlights: • Synthesis of Fe doped In{sub 2}O{sub 3} powders using a solid state reaction. • Characterization of the samples using XRD, UV–vis-NIR, FT-IR, and VSM. • All Fe doped In{sub 2}O{sub 3} powders exhibited the cubic structure of In{sub 2}O{sub 3}. • All the Fe doped In{sub 2}O{sub 3} samples exhibited room temperature ferromagnetism. - Abstract: Iron doped indium oxide dilute magnetic semiconductor (In{sub 1−x}Fe{sub x}){sub 2}O{sub 3} (x = 0.00, 0.03, 0.05, and 0.07) powders were synthesized by standard solid state reaction method followed by vacuum annealing. The effect of Fe concentration on structural, optical, and magnetic properties of the (In{sub 1−x}Fe{sub x}){sub 2}O{sub 3} powders have been systematically studied. X-ray diffraction patterns confirmed the polycrystalline cubic structure of all the samples. An optical band gap increases from 3.12 eV to 3.16 eV while Fe concentration varying from 0.03 to 0.07. Magnetic studies reveal that virgin/undoped In{sub 2}O{sub 3} is diamagnetic. However, all the Fe-doped In{sub 2}O{sub 3} samples are ferromagnetic. The saturation magnetization (M{sub s}) of ferromagnetic (In{sub 1−x}Fe{sub x}){sub 2}O{sub 3} (x = 0.03, 0.05, and 0.07) samples increases from 11.56 memu/g to 148.64 memu/g with x = 0.03–0.07. The observed ferromagnetism in these samples was attributed to magnetic nature of the dopant (Fe) as well as defects created in the samples during vacuum annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanoscale oxidation behavior of carbon fibers revealed with in situ gas cell STEM

Thermal protection systems are used to protect spacecraft payloads during the extreme conditions of atmospheric entry. The backbone of the composite material often used for NASA mission is carbon fiber, which oxidizes at these conditions. This study presents the direct observation of carbon oxidation using in situ Scanning Transmission Electron Microscopy (STEM). A thin section of a commercially-available carbon fiber material containing multiple structures was examined by STEM in a closed-environmental cell in which temperature was raised from 25 to 1050 °C under a steady flow of air. Results show that the random polycrystalline carbon structure oxidized more uniformly and rapidly than the single crystallite region, which oxidized more anisotropically. These findings are the first to directly observe the structural dependence of carbon oxidation rates at these length-scales while also giving important insight into the onset of pitting at various active surface sites, important pieces in fundamentally understanding of carbon oxidation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Microstructural, optical and ethanol sensing properties of sprayed Li-doped Mn{sub 3}O{sub 4} thin films

Highlights: • Li doped Mn{sub 3}O{sub 4} was grown on glass substrate via the low cost effective spray pyrolysis technique. • Li doping notably tuned the optical band gap of Mn{sub 3}O{sub 4} thin film. • The incorporation of Li ions was found to provide an enhancement of ethanol sensitivity. - Abstract: Lithium-doped manganese oxide thin films have been deposited onto glass substrate by the spray pyrolysis technique. The effect on structural, morphological, optical and ethanol sensitivity properties of the films with different Li concentrations was investigated. The X-ray diffraction (XRD) studies of Li doped Mn{sub 3}O{sub 4} thin films revealed polycrystalline tetragonal structure with lattice parameters: a = 5.73 Å and c = 9.46 Å. The most intense band at 653.26 cm{sup −1} observed in room temperature Raman spectrum of all films corresponds to the tetragonal crystal structure of Mn{sub 3}O{sub 4}. Optical band gap energy was found to vary in the range of 2.23–2.82 eV by an increase in Li-doping concentration up to 15%. The resistance based gas sensing measurements showed a clear response already at a low ethanol concentration of 0.1%. The films showed promising ethanol sensing behavior; especially the sample doped with 3% of lithium exhibits the most excellent sensing performance.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structure and mechanical properties of 3dTM ion doped RF sputtered ZnO thin films on Si (100)

Mn, Fe and Mn-Fe doped ZnO thin films were deposited on Si (100) substrates by rf- magnetron sputtering using ceramic target in pure oxygen gas environment. The X-ray diffraction shows the polycrystalline wurtzite structure films. The average grain size varies from 32-50 nm, with lower grain size for Fe doped ZnO films. The room temperature loading and unloading curve are continuous without any pop-in. The Young's modulus and hardness are in the range 156-178 GPa and 14-15.5 GPa respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Structure and Electronic Properties of Polycrystalline Dielectrics

We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Crystal structure and magnetic properties of Zn{sub 0.9}Cu{sub 0.1}O{sub y} rf-sputtered thin films

Zn{sub 0.9}Cu{sub 0.01}O thin films were deposited on quartz substrates by rf-magnetron sputtering using ceramic target in pure argon gas environment. The X-ray diffraction show the polycrystalline wurtzite structure of the films. The average grain size increases from 40-100nm as thickness of the film increases. The room temperature magnetization studies show the films to be ferromagnetic. The saturation magnetization decreases with increase in film thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of Extended Aqueous Processing on Structure, Chemistry, and Performance of Polycrystalline LiNi x Mn y Co z O 2 Cathode Powders

The prospect of aqueous processing of LiNi x Mn y Co z O 2 (NMC) cathodes has significant appeal to battery manufacturers for the reduction in materials cost, toxicological risk, and environmental impact compared to conventional N -methyl-2-pyrrolidone (NMP)-based processing. However, the effects of aqueous processing of NMC powders at industrial timescales are not well studied, with prior studies mostly focusing on relatively brief water washing processes. Here, we investigate the bulk and surface impacts of extended aqueous processing of polycrystalline NMC powders with different compositions. We demonstrate that at timescales of several hours, polycrystalline NMC is susceptible to intergranular fracture, with the severity of fracture scaling with the NMC nickel content. While bulk crystallinity and composition are unchanged, surface sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the exposure of water leads to a level of delithiation, nickel reduction, and reconstruction from the layered to rock-salt structure at the surface of individual grains. Dynamic single NMC microparticle compression testing suggests that the resulting mechanical stresses weaken the integrity of the polycrystalline particle and increases susceptibility of intergranular fracture. The initially degraded surfaces along with the increased surface area lead to faster capacity fade and impedance growth during electrochemical cycling. From this work, it is demonstrated that NMC powders require surface or grain boundary modifications to make industrial-scale aqueous cathode processing viable, especially for next-generation nickel-rich NMC chemistries.

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

Elasticity and yielding of mesophases of block copolymers in water–oil mixtures

Here, amphiphilic block copolymers self-assemble at the water/oil interface to form different mesomorphic structures, such as lamellar, micellar cubic, normal hexagonal, and reverse hexagonal structures. Usually, these structures are polycrystalline and the value of their elastic modulus depends on the average orientation of their constituent's single crystals. We introduce a model to predict the elastic modulus and yielding of mesophases from their characteristic length and intermicellar interactions. Shear modulus of each structure is measured as a function of deformation (strain). Zero-shear modulus, G 0 , depends on the inverse of the intermicellar distance with a power law model. The power law index for each structure is approximately n + 2 where n is the degree of confinement in the mesophase: 1 for lamellar, 2 for both normal and reverse hexagonal, and 3 for micellar cubic structures. Rheological properties of different mesophases of Pluronic P84 in the presence of water and p -xylene are used as a case study. The model is found to be in good agreement with experimental data in the linear viscoelastic region. When compared to experimental data, the yield strain value obtained from the model is one order of magnitude higher than the limit of the linear viscoelastic regime and close to the strain at the cross-over point of storage and loss moduli. Frequency sweep measurements are done to characterize the relaxation and cooperative model behaviors of each mesophase structure.

36 MATERIALS SCIENCE↗