Route to high-energy density polymeric nitrogen t-N via He−N compounds

Li, Yinwei; Feng, Xiaolei; Liu, Hanyu; Hao, Jian; Redfern, Simon A. T.; Lei, Weiwei; Liú, Dan; Ma, Yanming

doi:10.1038/s41467-018-03200-4

Cited by 147 publications

(99 citation statements)

References 54 publications

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“…The known compounds consisting of He are either charged molecular species such as helium hydride ion (HeH + ) 19,20 , or the pressure stabilized van der Waals compounds, such as Ne(He) 2 21,22 and He(N 2 ) 11 23 . Interestingly, He was also shown to form HeN 4 in a pressure range from 8.5 to 69 GPa 24 .…”

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confidence: 97%

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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confidence: 97%

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

et al. 2019

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“…The addition of helium can also reduce the pressure at which polymerization of nitrogen may occur. [35]. It has been reported that helium can react with water to form He(H 2 O) 2 at very high pressures (297 GPa) [36].…”

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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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“…The latest research has identified helium reacting at high P-T conditions with other elements or compounds, such as water [8], sodium and sodium oxide [9], nitrogen [10], and iron [11], but no connections to the deep-Earth helium reservoir have been established. Meanwhile, a theoretical analysis [12] shows that helium tends to react under high pressure with ionic compounds containing an unequal number of cations and anions.…”

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confidence: 99%