Searching for polynitrogen compounds has attracted great attention due to their potential applications as high energy density materials. Here, we report a facile approach to the synthesis of a solid lithium pentazolate (LiN5) compound by compressing lithium azide and molecular nitrogen under high pressure with laser heating. The formation of LiN5 with the crystal structure P21/m-LiN5 was identified according to the appearance of the vibrational modes of N5 – rings in Raman spectra and synchrotron X-ray diffraction measurements under high pressure. The LiN5 remains stable down to 18.5 GPa upon decompression. The bond lengths in N5 – are between single- and double-bond lengths. This study indicates that the precursor can effectively tune the high-pressure phase of pentazolate, providing us an alternative route to synthesize a polynitrogen compound with a novel structure.

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The pentazolate anion, cyclo-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 P21/c) through the chemical transformation of pure lithium azide under high-pressure and high-temperature conditions. Upon decompression, the structural transition from P21/c-LiN5 to P21/m-LiN5 at ∼15.6 GPa was observed for the first time. Cyclo-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.