High-Pressure Synthesis and Stability Enhancement of Lithium Pentazolate

Abstract

The pentazolate anion, <i>cyclo</i>-N₅^-, has received extensive attention as a new generation of energetic species for explosive or propulsion applications. Binary pentazolate compounds have been obtained under high-pressure conditions and their stability enhancement is crucial for obtaining more competitive high energy density materials (HEDMs). Here, we report the synthesis of a new solid phase of lithium pentazolate (space group <i>P</i>2₁/<i>c</i>) through the chemical transformation of pure lithium azide under high-pressure and high-temperature conditions. Upon decompression, the structural transition from <i>P</i>2₁/<i>c</i>-LiN₅ to <i>P</i>2₁/<i>m</i>-LiN₅ at ∼15.6 GPa was observed for the first time. <i>Cyclo</i>-N₅^- can be traced down to ∼5.7 GPa at room temperature and recovered to ambient pressure under a low-temperature condition (80 K). Our results reveal the enhancement of pentazolate anion stability with the increasing content of metal cations and demonstrate that low temperature is an effective route for the recovery of the pentazolate anion.