Structures of Molecular Nitrogen at High Pressures.

High-Pressure Chemistry of Carbon Nitride Materials

MRS Proceedings ◽

10.1557/proc-499-309 ◽

1997 ◽

Vol 499 ◽

Cited By ~ 4

Author(s):

Andrew J. Stevens ◽

Carl B. Agee ◽

Charles M. Lieber

Keyword(s):

High Pressure ◽

Carbon Nitride ◽

High Pressures ◽

Molecular Nitrogen ◽

Nitrogen Concentration ◽

Stability Limit ◽

Decomposition Temperature ◽

Threshold Temperature ◽

Arrhenius Behavior ◽

Decomposition Rates

ABSTRACTThe composition and properties of the sp2-bonded carbon nitride precursor paracyanogen (pCN) has been studied at high pressures and temperatures. Paracyanogen decomposes to carbon and molecular nitrogen with the decomposition temperature increasing with pressure over the range of 3 to 19 GPa. Prior to decomposition, pCN can be transformed to an atmospheric-pressure quenchable phase that is more than 25% higher in density and over an order of magnitude harder than the starting material. Structural analysis of this quenchable phase shows, however, that it consists of a sp2-bonded network. In addition, the decomposition kinetics of paracyanogen have been studied in detail. Rapid, self-propagating decomposition occurs above a threshold temperature. Below this, decomposition rates exhibit an Arrhenius behavior with activation energy and volume of 2.7 eV and 3.9 Å3, respectively The decomposition rates depend on the nitrogen density and decrease significantly with lower nitrogen concentration. Kinetic effects favoring a graphite-like, sp2-bonded structure may preclude the high-pressure synthesis of superhard, sp3-bonded carbon nitride solids below their thermodynamic stability limit, unless an optimally designed precursor is employed.

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Synthesis of magnesium-nitrogen salts of polynitrogen anions

Nature Communications ◽

10.1038/s41467-019-12530-w ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 16

Author(s):

Dominique Laniel ◽

Bjoern Winkler ◽

Egor Koemets ◽

Timofey Fedotenko ◽

Maxim Bykov ◽

...

Keyword(s):

High Pressures ◽

Molecular Nitrogen ◽

High Energy ◽

High Energy Density ◽

Ambient Conditions ◽

X Ray Diffraction ◽

X Ray ◽

High Energy Density Materials ◽

Polynitrogen Compounds ◽

Laser Heated

Abstract The synthesis of polynitrogen compounds is of fundamental importance due to their potential as environmentally-friendly high energy density materials. Attesting to the intrinsic difficulties related to their formation, only three polynitrogen ions, bulk stabilized as salts, are known. Here, magnesium and molecular nitrogen are compressed to about 50 GPa and laser-heated, producing two chemically simple salts of polynitrogen anions, MgN4 and Mg2N4. Single-crystal X-ray diffraction reveals infinite anionic polythiazyl-like 1D N-N chains in the crystal structure of MgN4 and cis-tetranitrogen N44− units in the two isosymmetric polymorphs of Mg2N4. The cis-tetranitrogen units are found to be recoverable at atmospheric pressure. Our results respond to the quest for polynitrogen entities stable at ambient conditions, reveal the potential of employing high pressures in their synthesis and enrich the nitrogen chemistry through the discovery of other nitrogen species, which provides further possibilities to design improved polynitrogen arrangements.

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