High-pressure low-temperature electrical properties of template-synthesized polypyrrole at low synthesis temperature: dimensional crossover under pressure

We have measured the pressure and temperature dependence of the electrical conductivity of thin films composed of doped polypyrrole microtubules with a diameter of 400 nm. The microtubules have been synthesized at 0 degrees C in a host membrane. The wall thickness of these microtubules can be contro lled by a variation of the synthesis time. The results of these measurement s are interpreted using the Mott Variable Range Hopping model. Samples comp osed of thin wall microtubules show a higher characteristic dimension of th e conduction process than samples composed of thick wall microtubules. Unde r pressure, the dimension of the hopping process increases and three-dimens ional behavior prevails for all investigated wall thicknesses of the microt ubules. Under pressure samples composed of thin wall microtubules show also a change of the temperature dependence of the pre-exponential factor in th e Mott law. The results suggest that the microtubules are not homogeneous b ut are composed of layers with different electrical conductivity behavior. (C) 1999 Elsevier Science B.V. All rights reserved.