Pressure-induced phase transitions in energetic materials revealed by single-crystal diffraction studies*

Understanding the high-pressure structure of energetic materials is essential for the realistic modeling of shock initiation and improvement of code. Pressure-induced structural phase transitions where the symmetry and structure are altered can be exceptionally difficult or impossible to unravel using conventional high-pressure powder X-ray diffraction (XRD). To address this problem, we performed single crystal (SC) XRD studies. In the case of TATB, an insensitive energetic material, our SCXRD results reveal a structural phase transition, reported for the first time, towards a monoclinic structure above 4-5GPa. These experimental results are further supported by calculations that suggest alteration of the stacking of the layers of the TATB molecules. We also investigate Al(IO3)3(HIO3)2(H2O)6, a promising energetic salt, and find through SCXRD a hexagonal to monoclinic phase change at \textasciitilde 6 GPa. These systems highlight the use of SCXRD in characterizing complex, high pressure phase changes.