Abstract
The high-pressure behavior of hydrazine has been investigated by in situ Raman spectroscopy and synchrotron X-ray diffraction experiments under pressure up to 46.5 and 33.0 GPa, respectively. It is found that the liquid hydrazine solidifies into phase I at about 1.2 GPa. The symmetry of phase I is confirmed to be space group P21 by the peak assignment, group theory analysis, and Rietveld refinement of XRD patterns. A solid–solid transition from phase I to phase II is observed in both Raman spectroscopy and XRD experiments at about 2.4 GPa, which is ascribed to the formation of new hydrogen bonds between hydrazine molecules. At 18.4 GPa, an isostructural transition from phase II to the final phase III is observed. The pressure-induced adjustment of bifurcated hydrogen bond is first researched and regarded as the origin of the isostructural transition. Above 20.6 GPa, a clear softening behavior occurs in the NH2 symmetric stretching mode. The coupling of optical vibrations derived from enhancement of the hydrogen bond is proposed as a crucial role in this softening process.
Published Version
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