Electron and optical microscopic studies of a stress-induced phase transition in 1,8-dichloro-10-methylanthracene

Abstract

Electron and optical microscopic studies of 1,8-dichloro-10-methylanthracene have revealed that the parent orthorhombic structure may, under certain circumstances, undergo a stress-induced phase transformation into a daughter structure. The overall process is one in which a single crystal is converted into another single crystal at an invariant plane the indices of which are shown to be (2–88, 0, 1) and the crystallographically equivalent (2–88, 0, 1). The transformation, which is akin to a martensitic process, may be regarded as the result of the operation of an invariant plane strain. The irrational habit plane is thought to be composed of stepped, close-packed planes the existence of which, in turn, suggests possible mechanisms for the formation of the interface between the two structures. Furthermore, the description of some of the properties of the interface may be formulated in terms of slip dislocations.

Recent comprehensive treatments of phase transitions in organic molecular crystals are unable to interpret such stress-induced transformations.