Crystalline LiN₅Predicted from First-Principles as a Possible High-Energy Material

Abstract

The search for stable polymeric nitrogen and polynitrogen compounds has attracted great attention due to their potential applications as high-energy-density materials. Here we report a theoretical prediction of an interesting LiN5 crystal through first-principles calculations and unbiased structure searching techniques. Theoretical calculations reveal that crystalline LiN5 is thermodynamically stable at pressures above 9.9 GPa, and remains metastable at ambient conditions. The metastability of LiN5 stems from the inherent stability of the N5(-) anions and strong anion-cation interactions. It is therefore possible to synthesize LiN5 by compressing solid LiN3 and N2 gas under high pressure and quench recover the product to ambient conditions. To the best of our knowledge, this is the first time that stable N5(-) anions are predicted in crystalline states. The weight ratio of nitrogen in LiN5 is nearly 91%, placing LiN5 as a promising high-energy material. The decomposition of LiN5 is expected to be highly exothermic, releasing an energy of approximately 2.72 kJ·g(-1). The present results open a new avenue to synthesize polynitrogen compounds and provide a key perspective toward the understanding of novel chemical bonding in nitrogen-rich compounds.

Pentazole and Ammonium Pentazolate: Crystalline Hydro-Nitrogens at High Pressure

“…High pressure substantially modifies the potential energy surface thus promoting unusual chemical bonding in the condensed phase. Recently, several N 5 -ring containing crystals have been predicted [12][13][14] and one of them, CsN 5 , has been synthesized at high pressures 15 .…”

The polymerization of nitrogen in Li2N2 at high pressures

“…The small difference has marginal effect on the description of the phase transitions. Additionally, we consider the decomposition formula of Li 2 N 2  → 2Li + N 2 , Li 2 N 2  → 2/3LiN 3  + 4/3Li, and Li 2 N 2  → 2/3Li 3 N + 2/3N 2 , in which Fm m, I 3d, Aba2, and Cmca structures for Li 22,23 , P4 1 2 1 2, I2 1 3, Pba2, and I  3m structures for N 2 3,4 , C2/m and P6/m structures for LiN 3 12 , P6/mmm, P6 3 /mmc, and Fm m structures for Li 3 N 7,8 , are adopted. As shown in Fig.…”

“…Also, it is possible to enhance the stability by introducing the metal element. Theoretically, Li 2 N 2 consisting ion is proved to be one of the stable stoichiometries in Li-N system under the pressure range from 0 to 100 GPa 7,8 . Moreover, to the best of our knowledge, the polymerization of Li 2 N 2 is not reported yet.…”

“…The cubic gauche structure (cg-N) with N-N single bonds was successfully synthesized above 110 GPa and 2000 K 2 , which prompts the further study on nitrogen-related materials. Recently, alkali metal-nitrogen systems are extensively studied and new compositions are reported theoretically 7–11 .…”

Amorphous polymerization of nitrogen in compressed cupric azide

“…It is found that ionization can effectively improve the stability of polynitrogen molecules. The pentazolate anion cyclo ‐N is of great interest in recent studies due to its potential application in high‐energy‐density materials . It can be stabilized using several chemical strategies, including metal salts and metal‐inorganic frameworks .…”