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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1967

Hall Mobility in SrTio (sub 3)

Conductivity and Hall coefficient measurements for electron mobilities in strontium titanate, discussing electron-phonon coupling and cryogenic experiments

ELECTRON MOBILITY↗
NASA NTRS1991

The timing of alkali metasomatism in paleosols

We have measured the concentrations of rubidium and strontium and 87Sr/86Sr values of whole-rock samples from three paleosols of different ages. The oldest of the three weathering horizons, the 2,760 Ma Mt. Roe #1 paleosol in the Fortescue Group of Western Australia, experienced addition of Rb, and probably Sr, at 2,168 +/- 10 Ma. The intermediate paleosol, developed on the Hekpoort Basalt in South Africa, is estimated to have formed at 2,200 Ma, and yields a Rb-Sr isochron age of 1,925 +/- 32 Ma. The youngest of the three paleosols, developed on the Ongeluk basalt in Griqualand West, South Africa ca. 1,900 Ma, yielded a Rb-Sr age of 1,257 +/- 11 Ma. The Rb-Sr systematics of all three paleosols were reset during post-weathering metasomatism related to local or regional thermal disturbances. The Rb-Sr systematics of the paleosols were not subsequently disturbed. The near-complete removal of the alkali and alkaline earth elements from these paleosols during weathering made them particularly susceptible to resetting of their Rb-Sr systematics. Paleosols of this type are therefore sensitive indicators of the timing of thermal disturbances.

NASA Discipline Number 52-20↗
NASA NTRS1992

Biostratigraphic and chemostratigraphic correlation of Neoproterozoic sedimentary successions: upper Tindir Group, northwestern Canada, as a test case

Recent advances in Proterozoic micropaleontology and sedimentary isotope geochemistry suggest that improved interbasinal correlation of Neoproterozoic (1000-540 Ma) successions is possible. Because widely varying interpretations of its age have been suggested and no reliable radiometric dates or paleomagnetic data are available, the upper Tindir Group of northwestern Canada provides an opportunity to test this hypothesis. The age of these strata is of paleontological importance because silicified carbonates near the top of the group contain disc-shaped-scale microfossils that may provide insights into the early evolution of biomineralization. A reinterpretation of upper Tindir microfossil assemblages suggests a late Riphean age. Although diagenesis and contact metamorphism have altered the isotopic compositions of some carbonates, least altered samples indicate that delta 13C of contemporaneous seawater was at least +4.7%, typical of Neoproterozoic, but not Cambrian, carbonates. Strontium isotopic compositions of the least altered samples yield values of approximately 0.7065, which can be uniquely correlated with late Riphean seawater. Together, micropaleontology and the isotopic tracers of C and Sr constrain the upper Tindir carbonates and their unique fossils to be late Riphean, likely between 620 and 780 Ma.

NASA Discipline Exobiology↗
NASA NTRS1999

The age of the carbonates in martian meteorite ALH84001

The age of secondary carbonate mineralization in the martian meteorite ALH84001 was determined to be 3.90 +/- 0.04 billion years by rubidium-strontium (Rb-Sr) dating and 4.04 +/- 0.10 billion years by lead-lead (Pb-Pb) dating. The Rb-Sr and Pb-Pb isochrons are defined by leachates of a mixture of high-graded carbonate (visually estimated as approximately 5 percent), whitlockite (trace), and orthopyroxene (approximately 95 percent). The carbonate formation age is contemporaneous with a period in martian history when the surface is thought to have had flowing water, but also was undergoing heavy bombardment by meteorites. Therefore, this age does not distinguish between aqueous and impact origins for the carbonates.

Carbonates/analysis↗
NASA NTRSDate not supplied

Morphological evolution and transition at nanoscale in BSTO ceramic materials

Considerable efforts have been devoted for the development of low cost ferroelectric and clean energy storage multifunctional materials. Modification in design and production of a low cost material with well proven process provides pathway for high energy density dielectric energy storage. We studied fluorine doped a commercially well-established material system barium strontium titanate with two different concentrations of dopants and studied the morphological transition and its effect on properties. It was observed that sample with higher concentration transitioned much faster into glassy state, followed by growth of fibers which turned into a self-arranged bird nest type shape. The sample with lower concentration changed slowly into glassy state and only few fibers were farmed. Dielectric was highly dependent on processing methods and shows variation with crystallinity of material, temperature and cooling conditions during processing. In the higher concentration range, we observed nano-scale interface breakdown very similar to that of solid-liquid interface breakdown during crystal growth.

dielectric↗