Here, we report the distinct behaviors of 4‐azidobenzoic acid (C7H5N3O2, 4‐ABA) in diamond anvil cells with the pressure up to ∼18 GPa at room temperature by in situ Raman scattering and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) measurements. The analyses of Raman spectra revealed that 4‐ABA underwent a phase transition in the pressure range of 0.8–1.3 GPa and a conformational change at 6.3 GPa, which were supported by XRD results. The phase transition is attributed to the distortion of the benzene ring, and the change of hydrogen bonds results in the conformational change. Above 11.2 GPa, the (112) Bragg peak moved toward a low angle, indicating the increase of the interplanar distance of 4‐ABA. Upon compression to 18.0 GPa, 4‐ABA transformed into amorphous phase that the low amorphization pressure is helpful for nitrogen polymerization. This study provides an effective route for understanding the evolution of the azide group under high pressure, which is beneficial to studying the mechanism of forming polymeric nitrogen.

Diphenylphosphoryl azide ((C6H5O)2P(O)N3, DPPA) was studied by in situ Raman scattering spectroscopy and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) technologies up to 11.6 GPa at room temperature. The analyses of Raman spectra revealed that the liquid DPPA transformed from Phase I to Phase II at 0.4 GPa and went to Phase III at 1.3 GPa. The first phase transition was attributed to the change of molecular conformation, and the second phase transition was induced by the deformation of benzene rings. The XRD results suggested that DPPA remained in a liquid state during the two phase transitions. The azide group became increasingly asymmetric under pressure and decomposed at 11.6 GPa. The low decomposition pressure of the azide group is conducive to the formation of polymeric nitrogen. Exploring the behaviors of the azide group under pressure might be helpful for understanding the potential application of DPPA in the synthesis of high energy density materials (HEDMs).