Using stepped anvils to make even insulation layers in laser-heated diamond-anvil cell samples

Du, Zhuofei; Gu, Tingting; Dobrosavljevic, Vasilije V.; Weir, Samuel T.; Falabella, S.; Lee, Kanani K. M.

doi:10.1063/1.4929667

Cited by 9 publications

(8 citation statements)

References 19 publications

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“…Each glass bead sample was cut in half, polished, and the composition was determined by electron probe microanalysis (EPMA) ( Tables 1, S1, and S2, see supporting information: section II) prior to being powdered and sample prepared with stepped anvils (Du et al, 2015). The stepped samples are then transferred to a diamond-anvil cell equipped with opposing flat culet anvils, which is then loaded with neon to provide thermal insulation and in situ pressure calibration (Zhuravlev et al, 2013).…”

Section: Methodsmentioning

confidence: 99%

The Role of Redox on Bridgmanite Crystal Chemistry and Calcium Speciation in the Lower Mantle

et al. 2020

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The amount of ferric iron Fe 3+ in the lower mantle is largely unknown and may be influenced by the disproportionation reaction of ferrous iron Fe 2+ into metallic Fe and Fe 3+ triggered by the formation of bridgmanite. Recent work has shown that Fe 3+ has a strong effect on the density and seismic wave speeds of bridgmanite and the incorporation of impurities such as aluminum. In order to further investigate the effects of ferric iron on mineral behavior at lower mantle conditions, we conducted laser-heated diamond-anvil cell (LHDAC) experiments on two sets of samples nearly identical in composition (an aluminum-rich pyroxenite glass) except for the Fe 3+ content; with one sample with more Fe 3+ ("oxidized": Fe 3+ /ΣFe~55%) and the other with less Fe 3+ ("reduced": Fe 3+ /ΣFe~11%). We heated the samples to lower mantle conditions, and the resulting assemblages were drastically different between the two sets of samples. For the reduced composition, we observed a multiphase assemblage dominated by bridgmanite and calcium perovskite. In contrast, the oxidized material yielded a single phase of Ca-bearing bridgmanite. These Al-rich pyroxenite samples show a difference in density and seismic velocities for these two redox states, where the reduced assemblage is denser than the oxidized assemblage by~1.5% at the bottom of the lower mantle and slower (bulk sound speed) by~2%. Thus, heterogeneities of Fe 3+ content may lead to density and seismic wave speed heterogeneities in Earth's lower mantle. Plain Language Summary Iron primarily exists in three oxidation states within the mantle: metallic iron (Fe 0), ferrous iron Fe 2+ (more reduced form), and ferric iron Fe 3+ (more oxidized form); however, the amount of Fe 3+ in the lower mantle is largely unknown. Recent work has shown that Fe 3+ has a strong effect on rock density and speed at which seismic waves travel through lower mantle minerals. In order to further investigate these effects, we conducted experiments on samples nearly identical in composition except for the Fe 3+ content. We compressed the samples between two diamonds and heated the sample to the conditions of Earth's lower mantle. For the reduced sample (low Fe 3+ content), we observed a complex assemblage of minerals, primarily composed of bridgmanite (the most abundant mineral in the Earth) and calcium silicate perovskite (a common secondary phase in the lower mantle). In contrast, the oxidized sample (high Fe 3+ content) yielded a single phase of these two minerals combined together as one mineral-a Ca-bearing bridgmanite. The resulting oxidized sample is lighter and seismic waves travel faster through it than the reduced sample. Thus, changes in Fe 3+ content may lead to density and seismic wave speed variations in Earth's lower mantle.

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Section: Methodsmentioning

confidence: 99%

The Role of Redox on Bridgmanite Crystal Chemistry and Calcium Speciation in the Lower Mantle

et al. 2020

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“…S1). The sample foils were loaded into preindented rhenium gaskets 15-30 µm thick using double-sided stepped anvils (43). Either KBr or Ar was used as a pressure-transmitting medium and as an insulation medium.…”

Section: Methodsmentioning

confidence: 99%

Evidence for Fe-Si-O liquid immiscibility at deep Earth pressures

Arveson

Deng

Karki

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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SignificanceEarth's outer core is composed of a liquid iron alloy with up to 10% of unknown light elements, likely silicon, oxygen, sulfur, carbon, or hydrogen. The release of these light elements upon freezing of the solid iron inner core plays an important role in sustaining Earth's magnetic field, but the exact chemical makeup of the core is widely debated. In this paper, we perform high-pressure, high-temperature melting experiments and first-principles simulations on iron alloys containing silicon and oxygen and find that two distinct liquids form at high pressures. The presence of immiscible liquids may explain a seismically observed stratified layer atop the outer core and suggests that an Fe-Si-O composition can explain multiple observations of the outer core.

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“…Using 200 or 300 μm culet diamonds, we compressed the SiC powder into an 80 or 125 μm drilled hole in a pre-indented rhenium gasket using the double-sided stepped anvil technique [15]. We gas loaded neon (Ne) [16] as a pressure medium and as thermal insulation (Fig.1).…”

Section: Methodsmentioning

confidence: 99%

Zinc-blende to rocksalt transition in SiC in a laser-heated diamond-anvil cell

Daviau

Lee

2017

Phys. Rev. B

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We explore the stability of the ambient pressure zinc-blende polymorph (B3) structure of silicon carbide (SiC) at high pressures and temperatures where it transforms to the rock-salt (B1) structure. We find that the transition occurs ~40 GPa lower than previously measured when heated to moderately high temperatures. A lower transition pressure is consistent with the transition pressures predicted in numerous ab initio computations. We find a large volume decrease across the transition of ~17%, with the volume drop increasing at higher formation pressures, suggesting this transition is volume driven yielding a nearly pressure-independent Clapeyron slope. Such a dramatic density increase occurring at pressure is important to consider in applications where SiC is exposed to extreme conditions, such as in industrial applications or planetary interiors.

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Using stepped anvils to make even insulation layers in laser-heated diamond-anvil cell samples

Cited by 9 publications

References 19 publications

The Role of Redox on Bridgmanite Crystal Chemistry and Calcium Speciation in the Lower Mantle

The Role of Redox on Bridgmanite Crystal Chemistry and Calcium Speciation in the Lower Mantle

Evidence for Fe-Si-O liquid immiscibility at deep Earth pressures

Zinc-blende to rocksalt transition in SiC in a laser-heated diamond-anvil cell

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