Transport properties of polypyrrole-ferric oxide conducting nanocomposites

Conducting nanocomposite samples were prepared combining colloidal ferric o xide particles with conducting polypyrrole. Three composite samples (prepar ed keeping colloidal content fixed and varying the content of the conductin g polypyrrole) and the pure polymer were used in the present investigation. Temperature dependent dc and ac conductivity and thermoelectric power for the samples have been measured. The dc conductivity results were analyzed b y Mott's variable range hopping mechanism. The variation of ac conductivity with the frequency shows very little change in total conductivity up to a critical frequency, followed by a sudden jump with discontinuity and then i ncreases monotonically following a power law. The frequency exponent decrea ses with temperature as predicted by the correlated barrier hopping theory. Above 50 K the ac component of the conductivity increases almost linearly as predicted by the quantum mechanical tunneling model. It is found that al l the features of ac conductivity cannot be reconciled into an existing sin gle theory. The thermoelectric power is positive, low, and varies linearly with temperature, indicating a metallic character and the presence of polar ons and/or bipolarons as the cationic charge carriers in the composites. Th e overall nature of the S(T) curves suggests that in addition to a contribu tion from hopping a linear metallike component is also active for the therm opower. (C) 2000 American Institute of Physics. [S0021-8979(00)04005-6].