Pressure-Induced Irreversible Phase Transition in the Energetic Material Urea Nitrate: Combined Raman Scattering and X-ray Diffraction Study

Abstract

In situ high-pressure Raman spectroscopy and synchrotron X-ray diffraction (XRD) have been employed to investigate the behavior of the energetic material urea nitrate ((NH2)2COH+·NO3 –, UN) up to the pressure of ∼26 GPa. UN exhibits the typical supramolecular structure with the uronium cation and nitrate anion held together by multiple hydrogen bonds in the layer. The irreversible phase transition in the range ∼9–15 GPa has been corroborated by experimental results and is proposed to stem from rearrangements of hydrogen bonds. Further analysis of XRD patterns indicates the new phase (phase II) has Pc symmetry. The retrieved sample is ∼10.6% smaller than the ambient phase (phase I) in volume owing to the transformation from two-dimensional (2D) hydrogen-bonded networks to three-dimensional (3D) ones. The mechanism for the phase transition involves the cooperativity of noncovalent interactions under high pressure and distortions of the layered structure. This work suggests high pressure is an efficient technique to explore the performance of energetic materials, and to synthesize new phases with high density.

Novel Gd(OH)3, GdOOH and Gd2O3 Nanorods: Microwave-Assisted Hydrothermal Synthesis and Optical Properties

“…This kind of interaction is directly related to the water capacity for electromagnetic radiation absorption and efficiency in converting electromagnetic radiation to thermal energy [25][26][27][28] . Therefore, the reaction time and temperature necessary for obtaining of such materials in this work is significantly lower than those described in the literature [29][30][31][32] providing a significant improvement on crystallinity and morphology.…”

A Novel High-Density Phase and Amorphization of Nitrogen-Rich 1H-Tetrazole (CH2N4) under High Pressure

“…This can give rise to the corrugation of the molecular sheet. Subsequently, phase transition and rearrangement of hydrogen-bond networks occur, in order to reduce the Gibbs free energy 32 33 . The pressure-induced crystalline-to-crystalline transition mechanism for 1H-tetrazole have some similarities with the layered adduct formed by cyanuric acid and Melamine (CA·M) 34 .…”

Pressure‐Induced Bond Rearrangement and Reversible Phase Transformation in a Metal–Organic Framework

“…[1] In general, the bonding characteristics of the parent and the product phases of PIPT remain invariant in conventional materials, while new chemical bond formation with PIPT is reported in only a handful of cases. [2][3][4][5][6][7][8] Even in such instances, the bond rearrangement is usually irreversible owing to the substantial strain induced under pressure; the few exceptions involve relatively minor changes. [6][7][8] For example, Crain et al reported that silicon undergoes a reversible pressure-induced structural transformation to give a different polymorph by simple dimerization of Si atoms in the unit cell, [6] and Olsen et al reported a similar phenomenon involving bond migration in Pb 3 Bi 2 S 6 .…”