Crystalline Structures and Energetic Properties of Lithium Pentazolate under Ambient Conditions.

Recently, it has been reported that high-pressure synthesized lithium pentazolates could be quenched down to ambient conditions. However, the crystalline structures of LiN under ambient conditions are still ambiguous. In this work, the structures of LiN compound were directly explored at atmospheric pressure by using a new constrain structure search method. By using this method, three new allotropes were confirmed, and they show lower energy than the previous reported LiN phases. Both their thermodynamic and dynamic stability were confirmed through formation enthalpies, phonon spectrum, and ab initio molecular dynamics simulations under ambient conditions. Moreover, these three allotropes show similar formation enthalpies and properties, which suggests that it is hard to obtain a single LiN phase, which is well consistent with the experimental phenomenon. Furthermore, because of their low formation energy, all of them possess low energy density when they directly decompose to LiN and nitrogen (0.52 kJ/g). Instead, the decomposed energy could be further improved to 3.78 kJ/g when they decompose under an oxygen-rich environment.