Optical constants and electrochromic characteristics of H_xMoO₃ and Li_xMoO₃ bronzes

Ellipsometric concentration dependent data of Z_xMoO₃ (Z=H⁺, Li⁺) bronze thin films are interpreted from different prospects to unravel a detailed account of electrochromic characteristics. From the linear parts of the electronic energy loss functions (-1/ϵ), and from the dips in the optical density data, it is very difficult to decide about crystallographic phase shifts in these bronzes, simply because of the difficulty of the structural determination of these microcrystalline materials. MoO₃ bronze thin films are found to have high electrochromic efficiency, and therefore require higher charge density, and less substoichiometry, to obtain the same contrast ratio as observed in tungsten bronze thin films. The values of oscillator strengths, dipole strengths, and the degrees of delocalization of polaron wave functions have been calculated at different doping levels, and all are found to reveal the characteristics of localized in-bandgap states of electrons, and do not give any symptom of formation of Bloch states in these bronzes even at higher values of concentration, x.