Structure and properties of a new κ-phase organic metal: (BEDT-TTF)2Cu2(CN)3

Abstract The electro-synthesis, structure and conductivity of a new κ-phase organic metal (BEDT-TTF) 2 Cu 2 (CN) 3 are described [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene C 10 H 8 S 8 ]. Partially oxidized BEDT-TTF cations form a structure similar to that found in the κ-phase superconductors, while Cu 2 (CN) 3 −1 anions form infinite two-dimensional sheets which alternate with layers of BEDT-TTF cations along the crystallographic a axis. The morphology and conductivity of the crystals are dependent on the electrocrystallization conditions. Samples prepared under certain conditions show a semiconductor-to-metal transition in the 10–30K range, while others have an immeasurably large resistance in this temperature range, even though the room-temperature crystal structures are identical, and EDX shows all samples to have the same composition. However, application of a thin layer of epoxy induces the transition in all samples, and enhances the low-temperature conductivity of some samples by a factor of about 100. Low temperature crystallographic measurements of the unit cell change on cooling indicate the epoxy-coating to reduce the thermal contraction of the samples, in particular in the direction of the crystallographic a-axis.