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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Fractal analysis of collision cascades in pulsed-ion-beam-irradiated solids [Collision cascade densities in ion pulsed ion irradiated solids { a fractal approach]

The buildup of radiation damage in ion-irradiated crystals often depends on the spatial distribution of atomic displacements within collision cascades. Although collision cascades have previously been described as fractals, the correlation of their fractal parameters with experimental observations of radiation damage buildup remains elusive. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 3C-SiC irradiated at 100 °C with ions of different masses. These data, together with results of previous studies of SiC and Si, are analyzed with a model of radiation damage formation which accounts for the fractal nature of collision cascades. Our emphasis is on the extraction of the effective defect diffusion length from pulsed beam measurements. Results show that, for both Si and SiC, collision cascades are mass fractals with fractal dimensions in the range of ~1–2, depending on ion mass, energy, and the depth from the sample surface. Within our fractal model, the effective defect diffusion length is ~10 nm for SiC and ~20 nm for Si, and it decreases with increasing cascade density. These results demonstrate a general method by which the fractal nature of collision cascades can be used to explain experimental observations and predict material’s response to radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evaluation of Cation Migration in Lanthanum Strontium Cobalt Ferrite Solid Oxide Fuel Cell Cathodes via In-Operando X-ray Diffraction

Anode-supported SOFC button cells with LSCF-6428 cathodes were operated at various temperatures under constant current conditions for hundreds of hours in dry or humid (~3% water) cathode air while continuously collecting 1 hour XRD scans throughout the test duration. Additionally, one cell in dry air was held at OCV, and 12% CO2 was added to the humid air for another cell. Long cumulative XRD count times allowed minor phases in concentrations of less than 0.1 wt% to be identified. In humid air, cell performance increased during the first couple of hundred hours. XRD measured a gradual shift of Fe-rich Fe,Co spinel peaks to lower angles while post-mortem SEM discovered nano-nodules on the LSCF surfaces. When 12% CO2 was added to humid air, performance degradation was observed after the initial conditioning response, unlike in tests without CO2, which were stable after conditioning. XRD also measured a shift in the peaks of the major LSCF phase in the test with CO2 indicative of some degree of gradual decomposition. Cells tested at constant current in dry air exhibited fast initial degradation that decelerated over time, while the cell held at OCV maintained a stable voltage. XRD of the cathodes held at OCV at 750 °C and operated at constant current at 700 °C in dry air measured a slower shift of the Fe-rich spinel peaks to lower angles than was seen in tests in humid air, along with a shift in the peaks of a Co-rich Fe,Co spinel to higher angles. Post-mortem SEM of cells exposed to dry air discovered smaller nano-nodules on the LSCF surfaces than had been present in cells tested in humid air. Cells tested at constant current in dry air at 750 °C and 800 °C did not exhibit any gradual changes in the XRD patterns nor were nano-nodules discovered.

Hardy, John S.↗
DOE OSTI2021

A porous supramolecular ionic solid

Charge decoration provides a new synthetic strategy to integrate discrete coordination cages into an extended permanently porous material.

Jackson, Nathan↗