Inhomogeneous doping of polyaniline doped with sodium-hexafluorophosphate (NaPF₆)

We report the charge transport properties of a polyaniline (PAN) sample doped with NaPF₆ (PAN-NaPF₆) by using the temperature dependent dc conductivity (σ_dc) and thermoelectric power, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) experiments. The σ_dc of the system is ∼ 0.8 S/cm at room temperature, and its temperature dependence follows a quasi one-dimensional (1D) variable range hopping (VRH) model. The thermoelectric power at room temperature is positive, implying hole transport in the system, and its temperature dependence is interpreted in terms of the metallic nature at high temperatures (≥ 150 K) and the quasi 1D VRH characteristics at low temperatures (≤ 150 K). The doping concentration of the sample is obtained from XPS experiments. The density of states of the PAN-NaPF₆ sample is estimated to be 1.18 st./(eV 2 rings), which is lower than that of conventional hydrochloric-acid-doped PAN (PAN-ES) samples. We compare the doping mechanism of PAN-NaPF₆ with that of PAN-ES based on the results of EPR and XPS argon-ion sputtering experiments. We observe that Na⁺ and counter ions mainly exist near the surface of the PAN-NaPF₆ sample and are inhomogeneously distributed through the sample.