Characterization of the Isothermal Compression Behavior of LLM-172

Area of Science:

• Materials Science
• High-Pressure Physics
• Spectroscopy

Background:

• Investigating energetic materials under extreme conditions is crucial for understanding their stability and behavior.
• 3,4-bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (LLM-172) is an energetic compound with a complex heterocyclic structure.

Purpose of the Study:

• To elucidate the high-pressure response of LLM-172 using complementary techniques.
• To determine the pressure-induced structural changes and decomposition pathways of LLM-172.

Main Methods:

• Raman spectroscopy was employed to probe vibrational modes up to 36 GPa.
• X-ray diffraction was used to analyze structural changes up to 50 GPa.
• First-principles density functional theory calculations were performed for comparison.

Main Results:

• Raman spectra showed peak broadening and loss of intensity above 20 GPa, with skeletal ring modes persisting.
• X-ray diffraction indicated the crystal maintained an orthorhombic structure to near 40 GPa.
• Decomposition/amorphization began near 10 GPa, suggesting a stable ring structure with low compressibility.

Conclusions:

• The skeletal ring structure of LLM-172 exhibits remarkable stability under high pressure.
• Decomposition of LLM-172 under pressure proceeds through isomerization, forming a C-O-N-O group, rather than direct ring cleavage.
• Raman spectroscopy and X-ray diffraction provide valuable insights into the high-pressure behavior of energetic materials.