DUAL ALKALI-METAL-ION CHANNEL STRUCTURES IN POLY(P-PHENYLENEVINYLENE)

X-ray-diffraction data from alkali-metal-doped poly(p-phenylenevinylen e) (PPV) have been compared with various candidate structures ascertai ned by Harris [A. B. Harris, Phys. Rev. B 50, 12441 (1994)] in a mean- field study of a model Hamiltonian which includes polymer-polymer and guest-host (i.e., alkali-metal-ion to polymer chain) interactions. At least one of these recently identified phases is found to have a local ordering motif that is consistent with data from K- and Rb-doped PPV samples at the highest alkali-metal concentrations. A closely related structure is found to be consistent with data from Na-doped PPV. These two structures form a class of channel structures whereby the well-kn own single alkali-metal-ion array/threefold polymer chain structure is replaced by a lower symmetry structure characterized by a staggered p air of parallel quasi-one-dimensional alkali-metal-ion arrays surround ed by four polymer chains.