Pressure-Induced Phase Transitions and Amorphization of 4-Carboxybenzenesulfonyl Azide

The in situ high-pressure phase transition behaviors of energetic material 4-carboxybenzenesulfonyl azide (C 7 H 5 N 3 O 4 S, 4-CBSA) have been investigated by the measurements of Raman scattering, mid-IR absorption, and angle-dispersive X-ray diffraction (ADXRD) in diamond anvil cells, the highest pressure in our studies was up to ∼14.6 GPa at room temperature. 4-CBSA transforms from phase I into phase II around 0.5–0.9 GPa, and then starts to going to phase III at about 2.5 GPa, phase II coexists with phase III until to about 5.5 GPa, the phase III of 4-CBSA finally begins to transform into amorphous state above 10.5 GPa. The first phase transition (phase I–II) of 4-CBSA is induced by the change of molecular conformation, and the second phase transition (phase II–III) is attributed to the distortion of benzene ring and the change of intermolecular O–H···O hydrogen bonds. The existence of sulfonyl group makes it much easier for the bent azide group to decompose under high pressure, which interpret that the amorphization pressure in 4-CBSA is much lower than that in benzyl azide. The unique behavior of the azide group may be helpful to understand the electron orbit hybridization and the formation of polymeric nitrogen.