High-Pressure Bonding Mechanism of Selenium Nitrides

Abstract

The high-pressure phase diagrams of binary Se–N system have been constructed using the CALYPSO method and first-principles calculations. Four stable compounds (Cmc21-SeN2, P21 /m-SeN3, P1̅-SeN4, and P1̅-SeN5) were identified at high pressures. Various peculiar nitrogen polymerization forms composed of single/double nitrogen–nitrogen bonds were found at the nitrogen-rich condition, such as N∞-chains in P21/m-SeN3, oligomeric N8-chains in P1̅-SeN4, and distorted N6 3– anion rings in P1̅-SeN5. Peculiar nitrogen polymerization forms make these compounds potential high-energy-density materials (HEDMs). Especially, P1̅-SeN5 has the highest energy density of 4.08 kJ g–1 among the selenium nitrides. The polymerization mechanism of nitrogen in the Se–N system has been explored using the “Lewis-like” two-center–two-electron and three-center–two-electron bonding analysis. Using the nitrogen-rich P1̅-SeN5 as a prototype, it is found that the famous N6 distortion in the polymerized nitrogen HEDM can be explained by the interatomic mechanical unbalance which is induced by the three-center two-electron bonding between the metal atom and the two neighboring nitrogen atoms.

Pressure-stabilized polymerization of nitrogen in manganese nitrides at ambient and high pressures

“…As the isovalue values of ELF are set as 0.8, no electron localization state is observed around the Mn atom, which indicates a weak ionic bond interaction between the Mn and N atom. 72 This is also in good agreement with the analysis of PDOS that little hybridization is observed between the Mn_3d and N_2p orbitals. In contrast, the large electron localization state between the N atoms means a strong N–N covalent bond interaction.…”

Neutral binary chalcogen–nitrogen and ternary S,N,P molecules: new structures, bonding insights and potential applications

“…3c,d In that context investigations of the high-pressure phase diagrams of the binary selenium-nitrogen system by Cui and co-workers reported in 2019 are of considerable interest. 52 These authors identified four stable compounds at high pressures: Cmc2 1 -SeN 2 , P2 1 /m-SeN 3 , P1-SeN 4 and P1-SeN 5 . As illustrated in Fig.…”

“…9, these novel nitrogen-rich materials are predicted to incorporate a variety of polynitrogen arrangements in the solid state. 52 The binary selenium nitride Cmc2 1 -SeN 2 has a layer structure ( Fig. 9a), while P2 1 /m-SeN 3 , P1-SeN 4 and P1-SeN 5 incorporate N ∞ -chains ( Fig.…”

“…The high energy-content of the latter three phases is reflected in the values of their energy densities, which are 3.27, 3.26 and 4.08 kJ g −1 , respectively. 52 Information on the dissociation barriers for these binary selenium nitrides is not available.…”

Polymerization of Nitrogen in Nitrogen–Fluorine Compounds under Pressure

“…At ambient conditions, the chemical energy released by the NF- Cmca phase is 1.84 eV/fu . The energy density of NF is compared to that of other reported nitrides AN x (A = B, H, Se, and S), − which share the property of covalent bonds between element A and nitrogen, as shown in Figure . Although NF has the lowest nitrogen fraction, its gravimetric energy density of 5.38 kJ/g is the highest among these compounds, surpassing that of TNT (4.30 kJ/g) and edging closer to HMX (5.70 kJ/g) .…”