Dual alkali-metal-ion channel structures in poly(p-phenylenevinylene)

X-ray-diffraction data from alkali-metal-doped poly($p$-phenylenevinylene) (PPV) have been compared with various candidate structures ascertained by Harris [A. B. Harris, Phys. Rev. B 50, 12 441 (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-known single alkali-metal-ion array/threefold polymer chain structure is replaced by a lower symmetry structure characterized by a staggered pair of parallel quasi-one-dimensional alkali-metal-ion arrays surrounded by four polymer chains.