Metallic electrical transport of PF6-doped polypyrrole: dc conductivity and thermoelectric power

We have measured the temperature dependence of conductivity and thermoelectric power of PF6-doped polypyrrole. The sample was electrochemically synthesized at -40 degrees C. The temperature coefficient of the conductivity changes the sign at T = 17 K where the conductivity becomes minimum. Thermoelectric power (TEP) measurement shows linear temperature dependence from room temperature down to 50 K characteristic to that of broad band metals, but a positive hump below 50 K is observed, Possibilities of the phonon drag effect due to the better crystallinity of the sample and/or the electron-phonon interaction in a disordered metallic state are discussed to understand the positive hump of TEP.