Broken symmetry interchain packing in lithium-doped polyacetylene: A combined x-ray/neutron diffraction study

Abstract Powder profiles have been obtained from unoriented films of (CH) x and (CD) x solution-doped with lithium by using x-ray and neutron diffraction respectively. Detailed intensity analyses show improved fits with a lower symmetry R3 model for the two-dimensional interchain packing, as compared to the previously proposed high-symmetry R3C space group. The R3-based structure is derived from the R3C one by a local distortion of the interchain packing motif, in a very similar way to the symmetry breaking observed in the tetragonal phases for larger alkali metals.