X-ray diffraction evidence for the formation of a discotic phase during graphitization

The low-angle peak with a spacing of 10 Angstrom observed in X-ray diffract ion scans of partially pyrolyzed aromatic molecules is attributed to the fo rmation of a liquid crystalline pre-graphitic phase that we identify as dis cotic. This conclusion is substantiated using data obtained for partially p yrolyzed 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). The crystall ine reflections of PTCDA are replaced by amorphous scattering during pyroly sis at 530 degreesC. In addition to the commonly observed amorphous carbon peak providing an interlayer spacing of about 3.5 Angstrom, a low-angle pea k corresponding to a 10 Angstrom spacing is observed in partially pyrolyzed PTCDA. Based on simulation of structure and diffraction patterns using mol ecular dynamic calculations, this peak is attributed to the distance betwee n columns of rotationally disordered, partially pyrolyzed PTCDA molecules i n a discotic phase. (C) 2001 Elsevier Science Ltd. All rights reserved.