Structural Tuning of Energetic Material Bis(1<i>H</i>‑tetrazol-5-yl)amine Monohydrate under Pressures Probed by Vibrational Spectroscopy and X‑ray Diffraction

Abstract

As a high-energy density material, bis­(1<i>H</i>-tetrazol-5-yl)­amine monohydrate (BTA·H₂O) was investigated at high pressures up to 25 GPa using in situ Raman spectroscopy, infrared spectroscopy, X-ray diffraction, and ab initio simulations. Upon compression, both the Raman and IR vibrational bands were found to undergo continuous and gradual broadening without significant change of the profile, indicating pressure-induced structural disordering rather than phase transition. X-ray diffraction patterns confirmed the pressure effect on the structural evolutions of BTA·H₂O. Upon decompression, the back transformation was observed with almost identical Raman and IR spectra and X-ray pattern of the recovered material, indicating the complete reversibility of the pressure-induced disordering of BTA·H₂O and thus the high chemical stability of the aromatic rings in BTA·H₂O. Interestingly, in contrast with all of other Raman and IR modes of BTA·H₂O, which exhibit blue shifts, the N–H stretching mode shows a prominent red shift upon compression to ∼8 GPa, strongly suggesting pressure-enhanced hydrogen bonding between BTA and H₂O. The analysis of X-ray diffraction patterns of BTA·H₂O indicates that the unit-cell parameters undergo anisotropic compression rate. The pressure dependence of the unit-cell parameters and volumes coincides with the behavior of the hydrogen-bonding enhancement. Aided with first-principles simulations, these pressure-mediated structural modifications consistently suggest that hydrogen bonding played an important role in the compression behavior and structural stability of BTA·H₂O under high pressures