Pressure-induced structural transition and low-temperature recovery of sodium pentazolate

Pentazolate compounds have attracted extensive attention as high energy density materials. The synthesis and recovery of pentazolate compounds is of great importance for their potential applications. Here, we report the synthesis of Pmn2 ₁-NaN ₅ and Pm-Na ₂N ₅ through compressing and laser heating pure NaN ₃ at ∼ 60 GPa. Upon decompression, the pressure-induced structural transition from Pmn2 ₁-NaN ₅ into Cm-NaN ₅ is observed in the pressure range of 14–23 GPa for the first time. The cyclo- ${\mathrm{N}}_5^{-}$ can be traced down to 4.7 GPa at room temperature and recovered to ambient pressure under low temperature condition (up to 160 K). The Pm-Na ₂N ₅ is suggested to decompose into the P4/ mmm-NaN ₂ at 23 GPa, and be stable at ambient conditions. This work provides insight into the high-pressure behaviors of pentazolate compounds and an alternative way to stabilize energetic polynitrogen compounds.