Systematizing structural modifications of BEDT-TTF-based organic conductors

A method is proposed to systematize a number of structural modifications of BEDT-TTF-based organic conductors and related materials. Different ways to pile up ring-over-bond (RB) (=90 °) or “ring-over-atom” (RA) (=60 °) overlap modes lead to various structures which are conventionally designated as β, β”, θ, α, and κ-phases. Many modifications of the β- and β″-phases are classified depending on various ways to introduce “dislocations” along the stacking axis. Systematic nomenclature to distinguish these modifications are proposed. Overlap of non-parallel molecules increases with decreasing the dihedral angle between the molecular planes. This accounts for the universal phase diagram of the θ-phase and the κ-phase compounds.