Plastic crystal behaviour in tetraethylammonium dicyanamide

The plastic crystal tetraethyl ammonium dicyanamide ([N-2,N-2,N-2,N-2][dca]) has been investigated with an emphasis on structure and dynamics in the plastic phase. It was found that almost all of the volume expansion occurs at the 11 -> I transition, with no volume expansion at the melt transition (as normally observed for crystals). The conductivity of this material shows a rapid increase at temperatures below the 11 -> 1 transition, reaching values similar to 10(-3) S/cm in Phase 1, and 0. 1 S/cm in the melt. The NMR measurements show that there is a sudden onset of rotational motions of the cations at the plastic transition; below this temperature the cations appear static. The rotational motion of the cation in Phase I has been discussed in terms of isotropic tumbling. (c) 2007 Elsevier B.V. All rights reserved.