Phonon-induced nonmetal-metal transition of a doped polyaniline

Abstract

We report the crossover for the microwave dielectric constant of camphor-sulfonic-acid-doped polyaniline prepared in m-cresol from very large room-temperature negative values to large positive ones with decreasing temperature below ${\mathit{T}}_{\mathit{s}}$∼20 K. We attribute this change to the transition from a phonon-controlled metallic state to a nonmetallic state with localized carriers and hopping transport below ${\mathit{T}}_{\mathit{s}}$. Electronically, one-dimensional chains that couple the three-dimensional crystalline regions are likely central for understanding the origin of this transition as weak localization. At T${\mathit{T}}_{\mathit{s}}$ we also observed an increase in the thermoelectric power and a linear decrease in the reduced activation energy for dc conductivity.