High-Pressure Equation of State of 1,3,5-triamino-2,4,6-trinitrobenzene: Insights into the Monoclinic Phase Transition, Hydrogen Bonding, and Anharmonicity

Abstract

The high-pressure equation of state (EOS) of energetic materials (EMs) is important for continuum and mesoscale models of detonation performance and initiation safety. Obtaining a high-fidelity EOS of the insensitive EM 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has proven to be difficult because of challenges in experimental characterization at high pressures (HPs). In this work, powder X-ray diffraction patterns were fitted using the recently discovered monoclinic I2/a phase above 4 GPa, which shows that TATB is less compressible than when indexed with the triclinic P1̅ phase. First-principles calculations were performed with Perdew−Burke−Ernzerhof (PBE) and PBE0 functionals including thermal effects using the P1̅ phase. PBE0 improves the description of hydrogen bonding and thus predicts accurate planar a and b lattice parameters under ambient conditions. However, discrepancies in the predicted lattice parameters above 4−10 GPa compared with experimental measurements indexed with P1̅ are further evidence of a structural modification at high pressure. Layer sliding defects are formed during molecular dynamics simulations, which induces an anharmonic effect on the thermal expansion of the c lattice parameter. In short, the results provide several insights into determining high-fidelity EOS parameters for TATB and other molecular crystals.

Strongly Anisotropic Thermomechanical Response to Shock Wave Loading in Oriented Samples of the Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-trinitrobenzene

“…Atomic-based studies of the nonshock mechanical response of TATB have also been reported. ,− ,,,− Because of the nature of the crystal packing, plasticity involving slip between basal planes in TATB (the crystal exhibits two inequivalent basal planes) is expected to occur with much lower barriers to dislocation glide ( i.e. , stacking-fault energies), in a fashion somewhat analogous to that in graphite, compared to slip that occurs within a given molecular layer or that involves dislocation glide across multiple basal planes (both of which involve disrupting the intermolecular hydrogen-bonding network that exists within the layers).…”

Fourier-like Thermal Relaxation of Nanoscale Explosive Hot Spots

“…Large and anisotropic conductivity values are typical of many hydrogen-bonded materials. ,,, In these respects, TATB provides an excellent bounding case for the thermal physics of explosives and for anisotropy in hydrogen-bonded materials more generally. A variety of orientation-dependent deformation mechanisms can activate in bulk TATB single crystal under shock and nonshock loads, including layer sliding, ,− buckling/twinning, ,, and dislocations that break the planar crystal layers whose hindered motions may serve as nuclei for shear band formation . The anisotropic thermal conductivity of TATB has been extensively characterized through molecular dynamics (MD) simulations as a function of temperature and pressure for both perfect (and near-perfect) single crystals − as well as the liquid state .…”

Strongly Anisotropic Thermomechanical Response to Shock Wave Loading in Oriented Samples of the Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)

“…Atomic-based studies of the non-shock mechanical response of TATB have also been reported. 22,[24][25][26]28,29,[67][68][69] Because of the nature of the crystal packing, plasticity involving slip between basal planes in TATB (the crystal exhibits two inequivalent basal planes) is expected to occur with much lower barriers to dislocation glide (i.e., stacking-fault energies), 70 in a fashion somewhat analogous to that in graphite, 71 compared to slip that occurs within a given molecular layer or that involves dislocation glide across multiple basal planes (both of which involve disrupting the intermolecular hydrogen-bonding network that exists within the layers). Indeed, using MD, very low stacking fault energies, and thus easy dislocation glide, were predicted for slip between adjacent basal planes both at zero kelvin 24 and at finite temperature.…”