Charge transport of lithium-salt-doped polyaniline

Charge transport properties, including temperature-dependent dc conductivity and thermoelectric power are reported for Li-salt (formula presented) or (formula presented) -doped polyaniline (PAN) samples. The experiments of electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) are performed for the systems. The electrical and magnetic properties and the doping mechanism of various Li-salt-doped PAN samples are compared with those of hydrochloric-acid (HCl) -doped PAN samples. The PAN materials doped with (formula presented) have the highest dc conductivity (formula presented) at room temperature) in the Li-salt-doped PAN systems studied here. The temperature dependence of (formula presented) of the systems follows a quasi-one-dimensional variable range hopping model, which is similar to that of HCl-doped PAN samples. As the molar concentration increases from (formula presented) to (formula presented) the system is transformed from an insulating to conducting (non-metallic) state. From EPR experiments, we measure the temperature dependence of magnetic susceptibility, and obtain the density of states for various Li-salt-doped PANs with different doping levels. We observe the increase of the density of states as the molar concentration increases. From the analysis of nitrogen (formula presented) peak obtained from XPS experiments, we estimate the doping level of the systems. We compare the effective doping thickness between HCl-doped PAN samples and Li-salt-doped PAN ones, based upon the results of XPS argon (Ar) ion sputtering experiments. The diffusion rate of (formula presented) or counterions and the dissociation constants of Li salt in doping solution play an important role for the effective doping and transport properties of the Li-salt-doped PAN samples.