Electrical conductivity and thermoelectric power of polypyrrole with different doping levels

The electrical conductivity and absolute thermoelectric power of the conducting polymer polypyrrole have been measured between approximately 4 K and 350 K. Normally-doped films had a conductivity of 26 Ω⁻¹ cm⁻¹, whilst lightly-doped films had a conductivity of 8 Ω⁻¹ cm⁻¹. The Mott variable-range hopping model for electrical conductivity is obeyed at higher temperatures for both types. The thermoelectric power is approximately linear in temperature, reaching about 5 μV K⁻¹ at 200 K, but is sublinear at higher temperatures and becomes constant above about 300 K. The Kuivalainen model, which explains the reported anomaly between optical and d.c. electrical conductivity, gives a good fit to the experimental data.