High-pressure induced structural changes of energetic ionic salts: Dihydroxylammonium 3,3′-dinitro-5,5′-bis-1,2,4-triazole-1,1′-diolate (MAD-X1)

Pressure-induced structural changes of dihydroxylammonium 3,3 '-dinitro-5,5 '-bis-1,2,4-triazole-1,1 '-diolate (MAD-X1), an insensitive energetic ionic salt with high detonation performance, was investigated under simu-lated conditions (0 to 10 GPa). Using the first-principles density-functional theory, the geometrical structure, intra/intermolecular interactions, electronic properties and Raman spectrum were calculated in detail to eluci-date material stability. The anisotropic compressibility in MAD-X1 was revealed by variations of lattice pa-rameters. Furthermore, combining internal hydrogen bonds and geometric parameters of each moiety, we could explain the abrupt changes on lattice constants from two aspects, which demonstrated the contribution of hydrogen bonding to decreasing the material sensitivity. Studies on band gap and partial density of state showed that excessive pressure probably inhibit the electron transfer. Additionally, the simulation of vibrational prop-erties suggested a possible phase transition at 7-8 GPa, implying that MAD-X1 could maintain its stability up to 7 GPa.