Phase Transition Routes for ε- and γ- CL-20 Crystals under High Pressure up to 60 GPa

The pressure-induced structural phase transitions of e- and γ- CL-20 were studied via the Raman and mid-infrared spectra up to 60 GPa. A phase transition of CL-20 from e-phase to γ′-phase starts at 0.9 GPa and completes at 4.4 GPa in this work. The γ′-phase in this work is distinctly different from the γ-phase recognized by the energetic community in terms of the structure and properties. Subsequently, η, starts at 6.9 GPa and completes at 10.6 GPa due to the slight cage distortion. With the further loading pressure, two new phases, φ and ι, were observed at 28 GPa and 50 GPa, respectively. Infrared results are consistent with Raman results and support the similar phase regions for CL-20 under high pressure. The behavior of γ-phase under pressure indicates that the ζ-phase appears at 1.3 GPa and sustains its stability up to 47.4 GPa. The current results prove that newly discovered γ′-phase is evidently distinct from the γ-phase and they undergo the different phase transition routes with the loading compre...