STRUCTURAL ASPECT OF METAL-INSULATOR-TRANSITION IN DOPED CONDUCTING POLYMERS

Partially crystalline structure of doped polypyrrole and polyaniline i s investigated by the X-ray diffraction experiment and compared with t he results from transport measurements. The increase of crystallinity along the direction of polymer chain in pyrrolehexafluorophosphate (PP y-PF6) film indicates that intrachain disorder plays a critical role i n transport in the metallic regime of the metal-insulator (M-1) transi tion. The X-ray structure of doped polyaniline sample in the insulatin g regime close to the M-I transition boundary suggests that the temper ature dependence of electrical resistivity is related to the geometry of aligned polymer chains in crystalline region. In the far insulating regime, no clear relation to transport data is observed in the micros copic crystalline structure possibly due to a strong disorder from lar ge scale inhomogeneity.