ELECTRON LOCALIZATION AND CHARGE TRANSPORT IN POLY(O-TOLUIDINE) - A MODEL POLYANILINE DERIVATIVE

The electron localization is increased with increasing one dimensionality of a quasi-one-dimensional disordered system (quasi-1D-DS). This concept is tested by studying the electron localization in the methyl ring-substituted derivative of polyaniline (PAN), poly(o-toluidine) (POT). The studies include the measurements of temperature dependence of the dc conductivity sigma-dc(T), thermoelectric power S(T), microwave conductivity sigma-mw(T), and dielectric constant epsilon(T) at 6.5 GHz, dc susceptibility chi(T), electron paramagnetic resonance, and electric-field dependence of conductivity sigma(F). The experimental results showed greater electron localization in the HCl salt of POT than that of PAN, reflected in much smaller sigma-dc, sigma-mw, and epsilon, increased Curie susceptibility, and decreased Pauli-like susceptibility. The localization is attributed to the reduced interchain diffusion rate caused by decreased interchain coherence and increased interchain separation, both of which result from the presence of CH3 on the C6 rings. The T dependences of ln-sigma approximately -T-1/2 and S(T) approximately S0 + B/T are interpreted as quasi-1D variable-range hopping (VRH) between the nearest-neighboring chains. Within the model, sigma(F) approximately KF1/2 with K approximately T-1/2 can be understood. The charging energy limited tunneling model for granular metals and the three-dimensional VRH model with a Coulomb gap are not consistent with the experiments. Other possible mechanisms for electron localization and the general implications for control of dimensionality and conductivity are discussed.