High-Pressure Study of Two Polymorphs of 2,4,6-Trinitrotoluene Using Neutron Powder Diffraction and Density Functional Theory Methods

A high-pressure neutron diffraction study was conducted on polycrystalline samples of the two known polymorphs of 2,4,6-trinitrotoluene [monoclinic (m) and orthorhombic (o) TNT] under hydrostatic conditions. Isothermal equations of state were obtained for both polymorphic forms. Neither polymorph was observed to undergo a phase transition in the pressure region 0-5 GPa, with both polymorphs displaying smooth compression behavior across the pressure range. This differs somewhat from previous X-ray diffraction and Raman spectroscopy investigations in which discontinuities were observed in the P-V curves and spectral changes were reported at similar to 2 GPa. The high-pressure response of these materials is supported by dispersion-corrected density functional theory calculations which, while overestimating the experimental bulk moduli, give excellent agreement with the observed smooth compression response of both phases.