Sodium Pentazolate: a Nitrogen Rich Energetic Material

Sodium pentazolates NaN$_{\mathrm{5}}$ and Na$_{\mathrm{2}}$N$_{\mathrm{5}}$, new energetic materials, are discovered using first principles crystal structure search for the compounds of varying amounts of elemental sodium and nitrogen. The pentazole anion (N$_{\mathrm{5}}^{\mathrm{-}})$ is stabilized in the condensed phase by sodium Na$^{\mathrm{+}}$ cations at pressures exceeding 20 GPa, and becomes metastable upon release of pressure, i.e. at ambient conditions. The sodium azide (NaN$_{\mathrm{3}})$ precursor for the new compounds is predicted to undergo a chemical transformation above 50 GPa into sodium pentazolates NaN$_{\mathrm{5}}$ and Na$_{\mathrm{2}}$N$_{\mathrm{5}}$. The calculated Raman spectrum of NaN$_{\mathrm{5}}$ is in agreement with the experimental Raman spectrum of a previously unidentified substance appearing upon compression and heating of NaN$_{\mathrm{3}}$ precursor, thus confirming the appearance of the new compound.