High‐Pressure Synthesis and Characterization of the Alkali Diazenide Li₂N₂

Novel lithium-nitrogen compounds at ambient and high pressures

“…Our calculated lattice constants of Immm structure ( Fig. 3d ) are in good agreement with experimental results 15 . The predicted N-N bond length is 1.271 Å, slightly smaller than the experiment.…”

“…The phase of Li 3 N is a semiconductor with the DFT band gap of 0.84 eV. All three stable phases of Li 2 N 2 are also metallic, in agreement with experiment 15 . Interestingly, LiN 2 has a metal-insulator transition: P6 3 /mmc is metallic at low pressure, but semiconducting in the high-pressure phase, with the band gap of 0.13 eV at 60 GPa.…”

“…For LiN (actually Li 2 N 2 ), the obtained structure at 0 GPa is Pmmm, which is consistent with the previous theoretical result 14 . At 8.2 GPa, Pmmm phase of LiN transforms into the Immm structure, indicating that the experimental result obtained at around 9 GPa is also perfectly correct 15 . At 8.9 GPa, the Immm structure will lose its stability and the Pnma phase becomes stable in the pressure range from 8.9 to 66.4 GPa.…”

“…Since then, discovery of new diazenides has been of constant interest. In 2010, alkali diazenides Na 2 N 2 and Li 2 N 2 (Pmmm) were predicted 14 , but then, a different structure of Li 2 N 2 (Immm) was obtained under HP/HT conditions (9 GPa, 750 K) by decomposition of LiN 3 15 . This discrepancy encourages us to study Li 2 N 2 under high pressure in detail.…”

All‐Nitrogen Analogue of Ozone: Li3N3 Species

“…In 2001, Kniep et al [11] synthesized binary diazenides SrN 2 and BaN 2 , proving the existence of the homonuclear dinitrogen anion N 2 2À , which is a deprotonated diazene N 2 H 2 with a N=N bond. Recently, Schnick et al [12] experimentally confirmed the stability of the first alkali diazenide Li 2 N 2 under high pressure/high temperature (HP/HT) conditions. As for theoretical reports, by using density functional theory (DFT) calculations, Bartlett et al [13] showed that lithium substitution on hydrogen positions of N 2 H 4 -N 5 H 5 hydrazines increases the specific impulse value (Isp, the force with respect to the amount of propellant used per unit of time) without lowering the lowest dissociation frequency of these compounds, thus implying their potential use as HEDM molecules.…”