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Results for “ZIRCONATES”

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 OSTI2016

Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons

Here, we present the results of a coordinated SIMS U–Pb, trace element, Ti-in-zircon thermometry, and microstructural study of 155 lunar zircons separated from Apollo 14, 15, and 17 breccia and soil samples that help resolve discrepancies between the zircon data, the lunar whole rock history and lunar magma ocean crystallization models. The majority of lunar grains are detrital fragments, some nearly 1 mm in length, of large parent crystals suggesting that they crystallized in highly enriched KREEP magmas. The zircon age distributions for all three landing sites exhibit an abundance of ages at ~4.33 Ga, however they differ in that only Apollo 14 samples have a population of zircons with ages between 4.1 and 3.9 Ga. These younger grains comprise only 10% of all dated lunar zircons and are usually small and highly shocked making them more susceptible to Pb-loss. These observations suggest that the majority of zircons crystallized before 4.1 Ga and that KREEP magmatism had predominantly ceased by this time. We also observed that trace element analyses are easily affected by contributions from inclusions (typically injected impact melt) within SIMS analyses spots. After filtering for these effects, rare-earth element (REE) abundances of pristine zircon are consistent with one pattern characterized by a negative Eu anomaly and no positive Ce anomaly, implying that the zircons formed in a reducing environment. This inference is consistent with crystallization temperatures based on measured Ti concentrations and new estimates of oxide activities which imply temperatures ranging between 958 ± 57 and 1321 ± 100 °C, suggesting that zircon parent magmas were anhydrous. Together, the lunar zircon ages and trace elements are consistent with a ≤300 My duration of KREEP magmatism under anhydrous, reducing conditions. We also report two granular texture zircons that contain baddeleyite cores, which both yield 207 Pb– 206 Pb ages of 4.33 Ga. These grains are our best constraints on impact ages within our sample population, and suggest at least one large impact is contemporaneous with the most common time of magmatic zircon formation on the Moon’s crust visited by the Apollo missions.

58 GEOSCIENCES↗
DOE OSTI2018

Atom probe tomography analysis of the reference Zircon GJ-1: An interlaboratory study

In recent years, atom probe tomography (APT) has been increasingly used to study minerals, and in particular the mineral zircon. Zircon (ZrSiO 4 ) is ideally suited for geochronology by utilising the U-Th-Pb isotope systems, and trace element compositions are also widely used to constrain petrogenetic processes. However, while standard geoanalytical techniques provide information at micron scale lengths, the unique combination of chemical/isotopic sensitivity and spatial resolution of APT allows compositional and textural measurements at the nanoscale. This round robin study aims to define the reproducibility of APT data across research facilities and assess the role of different aspects of the atom probe workflow on reproducibility. This is essential to allow correct evaluation of APT results and full utilization of this emerging technique within the geoscience community. In this study, nine samples from the same homogemeous, GJ-1/87 zircon reference grain were sent to nine APT institutes in Europe, USA, Canada and Australia. Each institute conducted three different rounds of APT analyses: using (i) unconstrained analysis parameters, [1] pre-defined analysis parameters, and (iii) a data analysis exercise. Data such as the measured composition, acquisition parameters, or mass spectrum peak identifications, were recorded and analyzed. We observe a significant variation in the measured composition across this round robin study as well as the number of trace elements identified. These differences are thought to directly result from the user's choice of peak identification, ranging and background correction model. The type of instrument does not seem to be a critical factor. Consequently, comparison of absolute trace element data on zircon using APT between laboratories is only valid if the same workflow has been ensured.

round robin, atom probe tomography, reference zirc↗
DOE OSTI2018

Influence of Nonstoichiometry on Proton Conductivity in Thin-Film Yttrium-Doped Barium Zirconate

Proton-conducting perovskites have been widely studied because of their potential application as solid electrolytes in intermediate temperature solid oxide fuel cells. Structural and chemical heterogeneities can develop during synthesis, device fabrication, or service, which can profoundly affect proton transport. Here, we use time-resolved Kelvin probe force microscopy, scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations to intentionally introduce Ba-deficient planar and spherical defects and link the resultant atomic structure with proton transport behavior in both stoichiometric and nonstoichiometric epitaxial, yttrium-doped barium zirconate thin films. The defects were intentionally induced through high-temperature annealing treatment, while maintaining the epitaxial single crystalline structure of the films, with an overall relaxation in the atomic structure. As a result, the annealed samples showed smaller magnitudes of local lattice distortions because of the formation of proton polarons, thereby leading to decreased proton-trapping effect. This resulted in a decrease in the activation energy for proton transport, leading to faster proton transport.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Additive effects of electronic and nuclear energy loss in irradiation-induced amorphization of zircon

We used a combination of ion cascades and the unified thermal spike model to study the electronic effects from 800 keV Kr and Xe ion irradiation in zircon. We compared the damage production for four cases: (a) due to ion cascades alone, (b) due to ion cascades with the electronic energy loss activated as a friction term, (c) due to the thermal spike from the combined electronic and nuclear energy losses, and (d) due to ion cascades with electronic stopping and the electron-phonon interactions superimposed. As a result, we found that taking the electronic energy loss out as a friction term results in reduced damage, while the electronic electron-phonon interactions have additive impact on the final damage created per ion.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Radiation-induced disorder in compressed lanthanide zirconates

For this study, the effects of swift heavy ion irradiation-induced disordering on the behavior of lanthanide zirconate compounds (Ln 2 Zr 2 O 7 where Ln = Sm, Er, or Nd) at high pressures are investigated. After irradiation with 2.2 GeV 197 Au ions, the initial ordered pyrochlore structure (Fm$\bar{3}$m) transformed to a defect-fluorite structure (Fm$\bar{3}$m) in Sm 2 Zr 2 O 7 and Nd 2 Zr 2 O 7 . For irradiated Er 2 Zr 2 O 7 , which has a defect-fluorite structure, ion irradiation induces local disordering by introducing Frenkel defects despite retention of the initial structure. When subjected to high pressures (>29 GPa) in the absence of irradiation, all of these compounds transform to a cotunnite-like ( Pnma ) phase, followed by sluggish amorphization with further compression. However, if these compounds are irradiated prior to compression, the high pressure cotunnite-like phase is not formed. Rather, they transform directly from their post-irradiation defect-fluorite structure to an amorphous structure upon compression (>25 GPa). Defects and disordering induced by swift heavy ion irradiation alter the transformation pathways by raising the energetic barriers for the transformation to the high pressure cotunnite-like phase, rendering it inaccessible. As a result, the high pressure stability field of the amorphous phase is expanded to lower pressures when irradiation is coupled with compression. The responses of materials in the lanthanide zirconate system to irradiation and compression, both individually and in tandem, are strongly influenced by the specific lanthanide composition, which governs the defect energetics at extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff

We report zircon crystals offer a unique combination of suitability for high-precision radiometric dating and high resistance to alteration. Paleomagnetic experiments on ancient zircons may potentially constrain the history of the earliest geodynamo, which would hold broad implications for the early Earth's interior and atmosphere. However, the ability of zircons to record accurately the geomagnetic field has not been demonstrated. Here we conduct thermal and alternating field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons from the Bishop Tuff, California. The rapid emplacement of these zircons in a well-characterized magnetic field provides a high-fidelity test of the zircons' intrinsic paleomagnetic recording accuracy. Successful dual heating experiments on eleven zircons measured using a superconducting quantum interference device (SQUID) microscope yield a mean paleointensity of (1σ; after excluding possible maghemite-bearing zircons), which is consistent with high-precision results from Bishop Tuff whole rock (). High-resolution quantum diamond magnetic (QDM) mapping, electron microscopy, and X-ray tomography indicate that the bulk of the remanent magnetization in Bishop Tuff zircons is carried by Fe oxides associated with apatite inclusions, which may be susceptible to destruction via metamorphism and aqueous alteration in older zircons. As such, while zircons can reliably record the geomagnetic field, robust zircon-derived paleomagnetic results require careful characterization of the ferromagnetic carrier and demonstration of their occurrence in primary inclusions. We further conclude that a combination of quantum diamond magnetometry and high-resolution imaging can provide detailed, direct characterization of the ferromagnetic mineralogy of geological samples.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗