Rare Helium-Bearing Compound 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>FeO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mi>He</mml:mi></mml:mrow></mml:math>
 Stabilized at Deep-Earth Conditions

Zhang, Jurong; Lv, Jian; Li, Hefei; Feng, Xiaolei; Lü, Cheng; Redfern, Simon A. T.; Liu, Hanyu; Chen, Changfeng; Ma, Yanming

doi:10.1103/physrevlett.121.255703

Cited by 79 publications

(49 citation statements)

References 59 publications

(82 reference statements)

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“…For example, dehydration melting at the top of the lower mantle could dramatically decrease the seismic velocities below a depth of 660 kilometers [10]. Accumulation of iron-enriched hydrous pyrite-type phase would reduce the speed of seismic waves at the core-mantle boundary, which may be detected at large low shear velocity provinces and ultra-low velocity zones [11][12][13]. Reservoirs of H also produce hydrides that would possibly infiltrate to the outer core [9,14].…”

Section: Introductionmentioning

confidence: 99%

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

et al. 2019

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Hydrogen in hydrous minerals becomes highly mobile as it approaches the geotherm of the lower mantle. Its diffusion and transportation behaviors under high pressure are important in order to understand the crystallographic properties of hydrous minerals. However, they are difficult to characterize due to the limit of weak X-ray signals from hydrogen. In this study, we measured the volume changes of hydrous ε-FeOOH under quasi-hydrostatic and non-hydrostatic conditions. Its equation of states was set as the cap line to compare with ε-FeOOH reheated and decompression from the higher pressure pyrite-FeO 2 Hx phase with 0 < x < 1. We found the volumes of those re-crystallized ε-FeOOH were generally 2.2% to 2.7% lower than fully hydrogenated ε-FeOOH. Our observations indicated that ε-FeOOH transformed from pyrite-FeO 2 Hx may inherit the hydrogen loss that occurred at the pyrite-phase. Hydrous minerals with partial dehydrogenation like ε-FeOOHx may bring it to a shallower depth (e.g., < 1700 km) of the lower mantle.

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Section: Introductionmentioning

confidence: 99%

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

et al. 2019

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“…Even a material as inert as helium can react with some elements and compounds under high pressure. For instance, a mixture with other inert gases [26,27], such as nitrogen [28,29], reacts with sodium [30], iron [31] or iron peroxide [32], alkali oxides or sulfide compounds [33] and alkaline earth fluorides [34]. The addition of helium can also reduce the pressure at which polymerization of nitrogen may occur.…”

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confidence: 99%

Multiple superionic states in helium–water compounds

et al. 2019

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Superionic states are phases of matter that can simultaneously exhibit some of the properties of a liquid and of a solid. For example, in superionic ice, hydrogen atoms can move freely while oxygen atoms are fixed in their sublattice. "Superionicity" has attracted much attention both in fundamental science and applications. Helium is the most inert element in nature and it is generally considered to be unreactive. Here we use ab initio calculations to show that He and H2O can form stable compounds within a large pressure range which can exist even close to ambient pressure. Surprisingly, we find that they can form two previously unknown types of superionic states. In the first of these phases the helium atoms exhibit liquid behavior within a fixed ice-lattice framework. In the second of these phases, both helium and hydrogen atoms move in a liquid-like fashion within a fixed oxygen sublattice. Because the He-O interaction is weaker than the H-O interaction, the helium atoms in these superionic states have larger diffusion coefficients and lower "melting" temperatures than that of hydrogen, although helium is heavier than hydrogen. The insertion of helium atoms substantially decreases the pressure at which superionic states may be formed, compared to those in pure ice.

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“…This driving force is so strong that He insertion could also occur in highly polarized covalent compounds such as SiO 2 30,31 . Similar mechanism might also promote the insertion of He into FeO 2 , a recently identified important mineral in the Earth's lower mantle that plays important role for the cycle of oxygen and water in Earth 32 . This rapid discovery of new He compounds inspires a new question: can He react with crystals of highly polarized molecules under pressure?…”

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confidence: 99%

Electrostatic force driven helium insertion into ammonia and water crystals under pressure

et al. 2019

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Helium, ammonia and ice are among the major components of giant gas planets, and predictions of their chemical structures are therefore crucial in predicting planetary dynamics.Here we demonstrate a strong driving force originating from the alternation of the electrostatic interactions for helium to react with crystals of polar molecules such as ammonia and ice. We show that ammonia and helium can form thermodynamically stable compounds above 45 GPa, while ice and helium can form thermodynamically stable compounds above 300 GPa. The changes in the electrostatic interactions provide the driving force for helium insertion under high pressure, but the mechanism is very different to those that occur in ammonia and ice. This work extends the reactivity of helium into new types of compounds and demonstrates the richness of the chemistry of this most stable element in the periodic table.

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Rare Helium-Bearing Compound FeO2He Stabilized at Deep-Earth Conditions

Cited by 79 publications

References 59 publications

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

Experimental Evidence for Partially Dehydrogenated ε-FeOOH

Multiple superionic states in helium–water compounds

Electrostatic force driven helium insertion into ammonia and water crystals under pressure

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