Role of lithium intercalation in fluorine-doped tin oxide thin films: Ab initio calculations and experiment.

Using a combination of experimental techniques and density functional theory (DFT) calculations, the influence of lithium insertion on the electronic and electrochemical properties of fluorine-doped SnO2 (FTO) is assessed. For this purpose, we investigate the electrochromic behavior of a commercial FTO electrode embedded in a solution of lithium perclorate (LiClO4). The electrochromic properties are evaluated by UV-vis spectroscopy, cyclic voltammetry, and chronoamperometry. These tests show that FTO exhibits electrochromism with a respectable coloration efficiency (η = 47.9 cm2/C at 637 nm). DFT study indicates that lithium remains ionized in the lattice, raising the Fermi level about 0.7 eV deep into the conduction band. X-ray photoelectron spectroscopy (XPS) is used to study chemical bonding and oxidation states. XPS analysis of the Sn 3d core levels reveals that lithium insertion in FTO induces a shift of 350 meV in the Sn 3d states, suggesting that lithium is incorporated into the SnO2 lattice.

A Comparative Study of the Electrical and Electromechanical Responses of Carbon Nanotube/Polypropylene Composites in Alternating and Direct Current.

The electrical and electromechanical responses of ~200 µm thick extruded nanocomposite films comprising of 4 wt.% and 5 wt.% multiwall carbon nanotubes mixed with polypropylene are investigated under an alternating current (AC) and compared to their direct current (DC) response. The AC electrical response to frequency (f) and strain (piezoimpedance) is characterized using two configurations, namely one that promotes resistive dominance (resistive configuration) and the other that promotes the permittivity/capacitive contribution (dielectric configuration). For the resistive configuration, the frequency response indicated a resistive-capacitive (RC) behavior (negative phase angle, θ), with a significant contribution of capacitance for frequencies of 104 Hz and above, depending on the nanotube content. The piezoimpedance characterization in the resistive configuration yielded an increasing impedance modulus (|Z|) and an increasing (negative) value of θ as the strain increased. The piezoimpedance sensitivity at f = 10 kHz was ~30% higher than the corresponding DC piezoresistive sensitivity, yielding a sensitivity factor of 9.9 for |Z| and a higher sensitivity factor (~12.7) for θ. The dielectric configuration enhanced the permittivity contribution to impedance, but it was the least sensitive to strain.