CORRELATION OF SEEBECK COEFFICIENT AND ELECTRIC-CONDUCTIVITY IN POLYANILINE AND POLYPYRROLE

We have measured the Seebeck coefficient and electric conductivity in the air-stable conducting polymers polyaniline and polypyrrole at diff erent doping levels. We find, at 300 K, the general correlation that t he logarithm of the electrical conductivity varies linearly with the S eebeck coefficient on doping, but with a proportionality substantially in excess of a prediction from simple theory for a single type of mob ile carrier. The correlation is unexpected in its universality and unf avorable in its consequences for thermoelectric applications. A standa rd model suggests that conduction by carriers of both signs may occur in these doped polymers, which thus leads to reduced thermoelectric ef ficiency. We also show that polyacetylene (which is not air stable), d oes exhibit the correlation with the expected proportionality, and, th us, its properties could be more favorable for thermoelectricity. (C) 1998 American Institute of Physics.