We explored the B–C–O system at pressures in the range 0–50 GPa by ab initio variable-composition evolutionary simulations in the hope of discovering new stable superhard materials. A new tetragonal thermodynamically stable phase B 4 CO 4 , space group I 4̄, and two low-enthalpy metastable compounds (B 6 C 2 O 5 , B 2 CO 2 ) have been discovered. Computed phonons and elastic constants show that these structures are dynamically and mechanically stable both at high pressure and zero pressure. B 4 CO 4 is thermodynamically stable at pressures above 23 GPa, but should remain metastable under ambient conditions. Its computed hardness is about 38–41 GPa, which suggests that B 4 CO 4 is potentially superhard.
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Electrostatic force driven helium insertion into ammonia and water crystals under pressure
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.
more » « less- Award ID(s):
- 1848141
- NSF-PAR ID:
- 10154250
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Communications Chemistry
- Volume:
- 2
- Issue:
- 1
- ISSN:
- 2399-3669
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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