Single Crystal Phase Transition in the Photoconductor p-Diiodobenzene

Abstract We have firmly established the presence of a single crystal to single crystal phase transition in p-diiodobenzene (C6H4I2) using optical microscopy and X-ray diffraction methods. This transition usually occurs at 51 ± 1 °C. The presence of a phase transition in this substance had been suggested by other workers to account for a precipitous drop in the charge carrier mobility in this general temperature vicinity. Our work suggests that this dramatic change in electrical behavior is produced by a rather small molecular reorientation.