Low-pressure metastable phase of single-bonded polymeric nitrogen from a helical structure motif and first-principles calculations

Abstract

Recognition of helical structural motifs in the experimentally observed cubic gauche ͑CG͒ crystal lattice has led to the discovery of a single-bonded nonlayered nitrogen structure that we have named chaired web ͑CW͒. First-principles density functional theory calculations reveal that CW, which was originally identified at high pressures, possesses metastability at ambient conditions as well. The metastability is demonstrated by both high-quality phonon dispersion calculations and finite-temperature first-principles molecular dynamics simulations. In addition, the CW phase is thermodynamically more stable than the CG phase in the ambient pressure regime.

Polymeric Nitrogen Chain Confined Inside a Silicon Carbide Nanotube

“…Moreover, after chemical reaction, these systems decompose into nitrogen gas, which is environmentally safe. A few forms of polymeric nitrogen have been predicted theoretically, [4][5][6][7][8][10][11][12] and one of them, the cubic gauche form, has already been experimentally demonstrated. 2 Unfortunately, none of them are stable at ambient conditions of the temperature and pressure.…”

“…We use the (4, 4), (5, 5), (6, 6), (7, 7), (6, 0), (7, 0), (8, 0) and (9, 0) SiCNTs to host the polymeric N-chain and perform a series of AIMD simulations for test. Our test simulations show that the armchair (6, 6) and zigzag (8,0) SiCNTs are suitable for hosting the polymeric nitrogen chain. All the armchair SiCNTs smaller in diameter than 6 6 SiCNT, as well as all the zigzag SiCNTs smaller than (8, 0) SiCNT, are too thin to host polymeric nitrogen chain; our test simulations using them result in nitrogen atoms attaching to the nanotube wall by forming N-Si chemical bonds.…”

“…First, we study the charge redistribution of the hybrid systems. To visualize it, we plot in Figures 3(a)-(b) the difference between electron density of N 16 @SiCNT(8, 0) and the superposition of electron density for isolated N 16 chain and SiCNT (8,0). From these panels, we know that the electrons accumulation and depletion are distributed around the polymeric nitrogen and near the wall of SiCNT, respectively.…”

“…1,2 However, there are continuous efforts searching for metastable polymeric nitrogen or polynitrogen. [2][3][4][5][6][7][8][9][10][11][12] These materials contain single N-N and double N N bonds, which have large energy difference compared to N≡N triple bond. Once the single (double) bonded nitrogen transforms to N 2 molecule, a large amount of energy is released.…”

Cagelike Diamondoid Nitrogen at High Pressures

“…This remarkable cg structure was later found to be more energetically stable than all the previously proposed polymeric structures. Subsequently, numerous low-energy theoretical high-pressure structures of polymeric nitrogen were proposed (e.g., Cmcm chain [10], chaired web [11], N 2 -N 6 [10], cis-trans chain [12], layered boat, eight-member rings, layered Pba2 [13], and the helical tunnel P2 1 2 1 2 1 structures [13,14]). It was established that the zero-temperature phase diagram of polymeric nitrogen at high pressures follows the transition sequence of cg → Pba2 (188-320 GPa) → P2 1 2 1 2 1 (>320 GPa).…”