Pressure- and Temperature-Dependent Structural Stability of LLM-105 Crystal

Abstract

The new energetic material 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5, LLM-105) maintains its structural stability under high pressure below 30 GPa at room temperature or in the temperature range from 513 to 5 K with ambient pressure based on the high pressure or the cryogenic X-ray diffraction patterns. One structural phase transition occurs at about 30 GPa and is confirmed by the pressure-dependent Raman and infrared spectra. The structure of the LLM-105 crystal shows anisotropic compressibility under pressure in the order βb > βa > βc and anisotropic thermal expansion in the order αb > αc ≈ αa. A Debye temperature of 1225 K is obtained for this crystal based on the lattice parameters at different pressures or temperatures. The experimental data reveal that compression is a better method to reduce the volume of the LLM-105 crystal compared with cooling. Raman and infrared spectra at extreme conditions suggest that the structural stability is contributed to the stronger inter- and intramolecular hydrogen-bonding networks within the LLM-105 crystal. The symmetric and asymmetric stretching modes of amino groups are coupled and it can improve the understanding of pressure evolution of the LLM-105 crystal. The bond constants of amino groups with different pressures and temperatures are also obtained.