Intrinsic transport properties in electrochemically prepared polythiophene doped with PF6−

We have studied the transport properties in polythiophene doped with PF6−. The intrinsic transport properties inherent in the crystallized regions were abstracted from the precise experiments of the d.c. resistivity ρdc(T), voltage-shorted-compaction (VSC) resistance ratio rVSC(T) and absolute thermoelectric power S(T) as a function of temperature at 1.6–300 K. At high temperatures between 35 and 80 K, rVSC(T) clearly exhibits a metallic behavior following the temperature dependence approximately expressed by T2.7, characteristic of the low- dimensional electronic structure. Unlike the behavior above 35 K, rVSC(T) increases steeply with decreasing temperature below 35 K. Corresponding to rVSC(T), S(T) also shows a metallic behavior at high temperatures, while at low temperatures an anomalous behavior is observed as reported in tetracyanoquinodimethane (TCNQ) salt. The results are interpreted in terms of a metal-insulator transition within the crystallized region that is believed to originate the fundamental transport character of conducting polymer as a novel low-dimensional metal.