Decomposition mechanism on different surfaces of copper azide

Copper azide, a potential primary explosives that may replace traditional primers such as lead azide, mercury fulminate and silver azide, has received widespread attention, but its decomposition mechanism remains unclear. Here, based on first-principles calculations, (010)_N3, (100)_N3 and (001) facets with a copper/nitrogen atom ratio of 1/6 are found to be the most stable surfaces of copper azide crystal. Through transition state (TS) calculations, we find that during the decomposition process on the surface, there is a synergy effect between two Cu–N1–N2–N3 chains, where the terminal N2–N3 bonds on two chains break simultaneously, and the dissociated N3 atom bonds with another N3' atom of adjacent chain to form a N₂ molecule. Next, the Cu–N bond will rupture, and two more N₂ molecules (N1–N2, N1'–N2') desorb from the surface. The overall reaction releases above 4 eV energy at a barrier of 1.23 eV on (001) surface. Electronic structure calculations reveal that the TS of N2–N3 rupture is more stabilized than that of N1–N2. According to the above results, we propose a new decomposition mechanism based on simulations of N–N bond breaking on different surfaces of copper azide. The results underscore the surface effect in decomposition of energetic materials.