jp7b00474_si_001.pdf (3.64 MB)
Emergence of Novel Polynitrogen Molecule-like Species, Covalent Chains, and Layers in Magnesium–Nitrogen MgxNy Phases under High Pressure
journal contribution
posted on 2017-04-21, 00:00 authored by Shuyin Yu, Bowen Huang, Qingfeng Zeng, Artem R. Oganov, Litong Zhang, Gilles FrapperStable
structures and stoichiometries of binary Mg–N compounds
are explored at pressures from ambient up to 300 GPa using ab initio
evolutionary simulations. In addition to Mg3N2, we identified five nitrogen-rich compositions (MgN4,
MgN3, MgN2, Mg2N3, and
Mg5N7) and three magnesium-rich ones (Mg5N3, Mg4N3 and Mg5N4), which have stability fields on the phase diagram.
These compounds have peculiar structural features, such as N2 dumbbells, bent N3 units, planar SO3-like
N(N)3 units, N6 six-membered rings, 1D polythiazyl
S2N2-like nitrogen chains, and 2D polymeric
nitrogen nets. The dimensionality of the nitrogen network decreases
as magnesium content increases; magnesium atoms act as a scissor by
transferring valence electrons to the antibonding states of nitrogen
sublattice. In this context, pressure acts as a bonding glue in the
nitrogen sublattice, enabling the emergence of polynitrogen molecule-like
species and nets. In general, Zintl–Klemm concept and molecular
orbital analysis proved useful for rationalizing the structural, bonding
and electronic properties encountered in the covalent nitrogen-based
units. Interestingly, covalent six-membered N64– rings containing P–1 (I) MgN3 phase is recoverable at atmospheric pressure. Moreover, ab initio
molecular dynamics analysis reveals the polymeric covalent nitrogen
network, poly-N42–, encountered in the
high-pressure Cmmm MgN4 phase can be preserved
at ambient conditions. Thus, quenchable MgN4, stable at
pressures above 13 GPa, shows that high energy-density materials based
on polymeric nitrogen can be achievable at reduced pressures. The
high-pressure phase P–1 (I) MgN3 with covalent N6 rings is the most promising HEDM candidate
with an energy density of 2.87 kJ·g–1, followed
by P–1 MgN4 (2.08 kJ·g–1).
History
Usage metrics
Categories
Keywords
High Pressure Stable structuresMgN 3polynitrogen molecule-like speciesMg 2 N 3quenchable MgN 4magnesium atoms actnitrogen sublatticecovalent N 6 ringscovalent nitrogen networkNovel Polynitrogen Molecule-like SpeciesMgN 3 phaseN 6 six-membered ringsN 2 dumbbellsN 3 unitsMg 5 N 3Mg 4 N 3Mg 5 N 7HEDM1 D polythiazyl S 2 N 2magnesium content increasesMg 3 N 2nitrogen network decreasesab initioCmmm MgN 4 phase
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC