Single wall carbon nanotube (SWNT) networks of different loadings were measured by impedance spectroscopy. The resistances of the junctions and bundles have been separated by modeling ac impedance spectroscopy data to an equivalent circuit of two parallel resistance-capacitance elements in series. The junction resistance was found to be 3–3.5 times higher than the bundle resistance. The dc and ac properties of the SWNT networks were found to obey a percolation scaling law, with parameters determined by dispersant type and SWNT purity. The values of the critical exponent in all cases were higher than the expected value of 1.3, which is related to widely distributed bundle and junction conductivities.

TiO2 is widely available as a chemically stable and harmless material. Recently, it has received a great deal of attention as a practical thermoelectric material. In this work, we studied the effects of aluminum (Al) doping concentration and lattice parameter on the thermoelectric properties of TiO2 at both room and high temperatures (475 °C). We found that the Al doping leads to a compression in the lattice constant and an increase in carrier concentration and consequently increases the electrical conductivity in the TiO2. We observed that the Al-doped TiO2 thin film shows a negative Seebeck coefficient and its value linearly decreases with increasing electrical conductivity. This result indicates that the Seebeck effect is developed by entropy-driven thermally assisted charge diffusion between low- and high-temperature surfaces. Further studies found that doping-induced reduction on entropy difference through electrical conductivity is accountable for the decrease of the Seebeck effect in the Al-doped TiO2. However, the Al doping can lead to phonon scattering at grain boundary interfaces and consequently decreases thermal conductivity. Therefore, the Al doping can essentially function as a mechanism to separately adjust electrical and thermal conductivities in the Al-doped TiO2. With Al doping, we obtained a maximal figure of merit (Z value) to be 1.30 at 475 °C and 0.48 At 23 °C from the Al-doped TiO2 at the doping concentration of 3%. The comparison of Z values between room and high temperatures confirms that thermally assisted charge diffusion and phonon scattering are two critical parameters for the development of efficient thermoelectric function in the Al-doped TiO2.