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Nitrogen-hydrogen-oxygen ternary phase diagram: New phases at high pressure from structural prediction

Authors: J. Shi, W. Cui, S. Botti, and M.A.L. Marques

Ref.: Phys. Rev. Mater. 2, 023604 (2018)

Abstract: Using an ab initio evolutionary structural search, we predict two novel crystalline phases in the H-N-O ternary phase diagram at high pressure, namely, NOH₄ and HNO₃ (nitric acid). Our calculations show that the C2/m phase of NOH₄ becomes stable at 71 GPa, while the P21/m phase of HNO₃ stabilizes at 39 GPa. Both phases remain thermodynamically stable at least up to 150 GPa, the maximum pressure we considered. The C2/m phase of NOH₄ contains two O-H layers and one dumbbell cluster layer, formed by two NH₃ molecules linked by a N-N covalent bond. The P21/m phase of HNO₃ contains a surprising quasiclover layer formed of H-N-O covalent bonds. Further calculations show that both phases are semiconducting, with band gaps of 6.0 and 2.6 eV for NOH₄ and NHO₃, respectively. Our calculations also confirm that the compound NOH₅ (NH₃H₂O) becomes unstable at pressures above 122 GPa, decomposing into NH₃ and H₂O.

Citations: 15 (Google scholar)

DOI: 10.1103/PhysRevMaterials.2.023604

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Bibtex:

@article{Shi_2018,
	doi = {10.1103/physrevmaterials.2.023604},
	url = {https://doi.org/10.1103%2Fphysrevmaterials.2.023604},
	year = 2018,
	month = {feb},
	publisher = {American Physical Society ({APS})},
	volume = {2},
	number = {2},
	author = {Jingming Shi and Wenwen Cui and Silvana Botti and Miguel A. L. Marques},
	title = {Nitrogen-hydrogen-oxygen ternary phase diagram: New phases at high pressure from structural prediction},
	journal = {Physical Review Materials}
}