Some Observations on the Structure of TATB

The recent discovery of second-harmonic light generation (SHG) from 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has renewed interest in both the crystallography and the identification of defect structures in this material. The accepted crystal structure is triclinic but centrosymmetric (P-1); SHG is not expected from materials of this symmetry. A wide variety of syntheses have been shown to produce SHG-positive materials, including an emulsion technique, two different recrystallization methods, and a variety of combined reaction - precipitation processes. In addition, two standard commercial powders have shown the property after annealing in the 300 C range. We have examined the structures of several of these powders using polarized light microscopy (PLM), scanning electron microscopy (SEM), and powder X-ray diffraction (XRD). We find that SHG-positive materials typically contain crystals both more transparent and more strongly faceted (i.e. ''more perfect'') than weak-SHG ones and that the positive samples show stronger texture in their powder diffraction patterns. These results are compared with predictions from Cady's structure