The Temperature Dependence of Conductivity Anisotropy in Intermediately Doped Polyacetylene

The temperature dependence of electrical conductivity and conductivity anisotropy of FeCI3 doped stretch-oriented polyacetylene film at different doping levels were measured by using Montgomery technique. The increase of conductivity anisotropy upon doping is related to the aligned fibrillar structure and the interfibrillar contact effect. Weak temperature dependence, the slight decrease at low temperature and the persistence of anisotropy through aging indicate that the interfibrillar contact barriers limit the quasi-one-dimensional charge transport in heavily doped polyacetylene and play a major role in the conductivity anisotropy. INTRODUCTION Since the first observation of the conductivity anisotropy of partially oriented polyacetylene film [1], various interpretations on the anisotropic transport mechanism have been presented [2, 3, 4], particularly in microscopic point of view based on the quasi-one-dimensional structure of polymer chain. With the developement of modified techniques for highly stretchable polyacetylene film [5], both the absolute magnitude of conductivity and its anisotropy increased up to ~rll ~10 4 S/cm and ¢rll/Cr.L ~10 2 [6], respectively. The proposed soliton-antisolton condensation model in heavily doped polyacetylene seems to be a successful phenomenological model for one-dimensional charge transport mechanism along the infinitely long polyacetylene chain [7, 8]. Although the intrinsic conductivity of polymer chain higher than 10 4 S/cm is expected, the bulk conductivity is limited by defects, interchain hopping process which is unavoidable due to the finite conjugation length, interfibrillar contact barriers, and so on. The fluctuation induced tunneling model [9] well describes the effect of interfibrillar contact resistance on the temperature dependence of conductivity in heavily doped polyacetylene, which is important in bulk conduction mechanism. In the same sense, weak temperature dependence of conductivity anisotropy could be understood as the contribution of identical metallic fibrils interfacing 0379-6779/93/$6.00 © 1993Elsevier Sequoia. All rights reserved