X-Ray Scattering from Sodium-Doped Polyacetylene: Incommensurate-Commensurate and Order-Disorder Transformations

Abstract

X-ray scattering carried out in situ during electrochemical doping indicates an unusual sequence of structural transitions. On doping to ^6-7 mole%, lightly doped regions coexist with a discommensurate-domain channel structure. As the Na concentration increases, the density of domain walls decreases. When the discommensuration density falls to zero, the Na channels form a commensurate VSxVJ superlattice with respect to the (average) triangular lattice of (CH)x chains. At still higher concentrations, the Na lattice becomes unstable and transforms into a disordered "fluid" phase within the ordered polyacetylene structure.

Controlled Molecular Assemblies of Electrically Conductive Polymers

“…The large number of equatorial reflections and off-axis reflections indicate a regular three dimensional arrangement of the polymer chains. The mosaic spread (derived from the half width at half maximum) is found to decrease to a value of about 3 0 as the draw ratio increases to ~1 0, comparable with that observed for polyacetylene prepared by the Durham method [80,81]. The strong small-angle reflections observed in the equatorial plane are connected with the long range order transverse to the polyacetylene chain direction.…”

“…The diffraction patterns for the doped samples indicate that the polyacetylene chain orientation remains essentially unchanged after doping. As observed in earlier studies [81], comparison of the fiber diffraction patterns of oriented t.r.ans.-polyacetylene before and after doping shows that the principal equatorial reflections remain with only modest shifts in their positions as a result of lattice expansion to accommodate the dopant counterions.…”

Solid-State Electrochemistry of the Li Single Wall Carbon Nanotube System

“…No voltage plateau was observed in the charge-discharge curves, indicating the absence of a staging mechanism via well-defined interstitial sites traditionally observed for alkali metal doping of graphite or polyacetylene. 1,2,5 There is no well-defined intercalation or deintercalation potential for Li into SWNT ropes; rather, insertion and removal proceed over a wide range of potentials, leading to steep voltage profiles similar to those of electrochemical capacitors. A large hysteresis was observed between charge and discharge; most of the Li was inserted below 0.25 V, while it was removed almost uniformly between 0 and 3 V. Such a large hysteresis was previously reported for ballmilled graphite, 19 balledmilled sugars, 21 and soft carbons containing substantial hydrogen.…”

“…Therefore, electrochemical doping has been used extensively to study the properties of carbon guest-host systems. In situ X-ray diffraction and electrochemical doping were used to study the phase diagram of Li x C 6 graphite, 1 phase transitions in Li-doped polyacetylene 2 and the structure of Li-doped solid C 60 . 3 In situ resistivity measurements were used to study the electronic transport properties of K-and Na-doped polyacetylene.…”

Electrochemical switching of conducting polymers: A variable resistance transmission line model

“…The electronic conductivity of the polymer can change by up to 6 orders of magnitude with oxidation state [15,16], from highly conducting and metal-like in the oxidized state to insulating in the reduced state [17]. Also, the concentration of ions in the polymer causes structural changes [18,19] that likely affect the porosity of the film, and the diffusivity of the ions [20,21].…”