THERMOELECTRIC-POWER OF DOPED POLYANILINE NEAR THE METAL-INSULATOR-TRANSITION

The thermoelectric power (S) of various doped polyaniline (PANI) near the metal-insulator (M-T) transition was investigated as a function of temperature (T), and compared with the characteristic temperature dep endence of conductivity (sigma). For the PANI protonated by camphor su lfonic acid (CSA), S(300K) = +8 similar to +12 mu V/K and linearly dep endent upon temperature, indicating that microscopic transport is via the diffusion of charge carriers in the extended electronic states wit h relatively narrow bandwidth. Zn the homogeneous limit, the thermoele ctric power is insensitive to the presence of microscopic disorder ass ociated with the critical behavior of sigma(T) near the M-I transition . For the samples doped by conventional protonic acids (HCl, H2SO4), t he large scale inhomogeneity induces the strong temperature: dependenc e of resistivity, rho(T) proportional to exp [(T-0/T)(1/2)], and addit ional negative contribution to the temperature dependence of thermoele ctric power.