Optical and electrochromic properties of annealed lithium-molybdenum-bronze thin films

Abstract

Optical band gaps, Urbach inverse slopes, and coloration bands of various samples of annealed, microcrystalline Li x MoO 3 -bronze thin films in the concentration range 0 Ͻ x Ͻ 0.6 were determined over the photon energy range from 0.4 eV to 4.2 eV. On investigation, it is learned that the measured, optical band gaps do not shift rigidly over the annealing temperature range 293 Յ T Յ 423 K and, therefore, do not reveal the Burstein-Moss effect or reflect any stable, crystallographic phase transformation during any investigated annealing cycle. A model relating the temperature-dependent optical gap to the real part of the refractive index has also been developed, and this model fits very well to the annealed data within a maximum error of about 20%. Next, using an oscillator model, a phonon energy of ϳ0.08 eV was obtained, which is very close to the characteristic phonon energy of the material, MoO 3 . Using this model, it becomes more certain that the contributions to the Urbach absorption edge for the annealed-molybdenum bronzes are coming from the structural and compositional disorder. In another finding, it was found that the absorption-peak energy for the annealed data was about 1.5-1.6 eV, which is still broad and asymmetrical, and therefore, it is almost of the Mo 6ϩ (or Mo 4ϩ )-Mo 5ϩ intervalence or polaronic type. Using the polaron model, the half-bandwidth of the coloration bands of investigated, annealed Li x MoO 3 -thin films was found to be almost constant, which is consistent with the nonrigid band behavior.

Physical properties and electrochemical performance of molybdenum–lead-germanate glasses and glass ceramics

“…The Mo 6 þ ions participate in the glass network within the [MoO 4 ] and [MoO 6 ] structural units while the Mo 5 þ ions act as modifiers. These mixed ionicelectronic conductor glasses have become a current topic mainly in applications such as electrochemical cells, highdensity memories, smart windows, electro-optical and electrochromic devices [11,12]. On the other hand, it is known that the Mo 5 þ ions are a sensitive indicator for the structural changes of the local symmetry in oxide glasses [13].…”

Thermo Optical Properties and Related Electronic Polarizabilities of MoO3 Thin Films Using Ellipsometry

“…It is also a fact in the litrature that the optical band gap energy depends on the temperature and it becomes smaller at higher temperature for MoO 3 thin films (Hussain, 2001). It should be noted that the dispersion of the refractive index has already been analysed (Hussain, 2002b) in terms of the E o (optical band gap) and E d (dispersion energy) using the single oscillator dispersion model of Wemple and Domenico (1971). Figure 13 shows that the film density goes on increasing as the temperature decreases from 297 to 120 K. The increase in the refractive index over the same temperature range can be noticed in Fig.…”

Thermo Optic Coefficients and Electronic Polarizabilities of Tungsten Bronzes Using Ellipsometry

“…Bronzes of different concentrations (or x-values) were obtained by controlling the rate of evaporation of Li (or Na) metal, and varying the time for their depositions. More details are given elsewhere [46], [47]. Hydrogen tungsten bronzes were prepared by passing hydrogen plasma into the WO 3 film at the pressure of 6 × 10 −1 torr.…”