Charge transport in the "emeraldine" form of polyaniline

The conductivity and the dielectric constant of the "emeraldine" form of polyaniline is studied in a wide range of frequency (dc, 10¹-10⁵ Hz, 6.5×10⁹ Hz), temperature (20K-340K) and protonation level (x ≡[C1]/[N] =0.0-0.5). Two distinct behaviors are observed: Firstly, for low protonation (x ≤ 0.13), hopping of charges between polarons and bipolarons leads to dipolar relaxation (ε{lunate}_RF(T)). Oscillation of polarons around pinning centers is suggested to be responsible for the high frequency dielectric constant of low protonated samples. Secondly, for intermediate to highly protonated samples (x > 0.22), the presence of "metallic islands" is apparent. Oscillation of charge carriers within the coherence length contributes to ε{lunate}_μω(T=0). The intrinsic conductivity within the islands is estimated to be of the order of 250 S/cm. The T-dependence of the dielectric constant indicates an increase of the coherence length with increasing temperature. The role of localization and the nature of "textured metallic islands" are discussed.