Cation Diffusivity in Nonstoichiometric Tungsten Trioxide Films

Abstract

Nonstoichiometric WO3−δ thin films, with oxygen deficiencies, δ, varying between 0.05 and 0.01, were prepared by RF sputtering. These values were determined by a method of chemical analysis consisting in the oxidation of the tungsten ion with less charge than +6 to W6+ by means of a KMnO4 solution. The electrochromic process in WO3−δ / MxWO3−δ, where M = H, Li, Na and 0.01 ≤ x ≤ 0.08, occurs reversibly. It is believed that the rate-controlling step of coloration is the diffusion of cation M+ into WO3−δ thin films. The cation diffusivity in the thin films was measured as a function of their δ and x values by means of a current-pulse-relaxation technique. The diffusivities, D, were about 5 × 10−10 cm2 s−1, 2 × 10−10 cm2 s−1, and 1 × 10−10 cm2 s−1 for H+, Li+, and Na+, respectively, in the stoichiometric films at 300 K. D values increased with an increase of oxygen deficiency and slightly increased or decreased with an increase of cation content. The pulse technique used may probably be responsible for the higher diffusivities obtained, as compared with results for similar systems provided by previous workers.

Enhancement of Electrochemical Properties of SIBs by Generating a New Phase in Potassium-Doped NaV6O15 Film Electrodes

“…The diffusion coefficient of Na + is of about the same order of magnitude as the previous results. ,, The diffusion coefficient decreases with the increase of annealing temperature, which is attributed to the diffusion coefficient of amorphous sample being higher than that of crystalline samples . In addition, it is noted that the diffusion coefficient of the anode is slightly higher than that of the cathode, which means that it is easier to remove sodium ions than to embed them.…”

Influence of Dopant Concentration on the Electrochromic Properties of Tungsten Oxide Thin Films

“…The diffusion coefficient for deintercalation varies from 3.056 x 10 -14 cm 2 s -1 to 8.853 x 10 -14 cm 2 s -1 . It is reported that the diffusion coefficient (D) exhibits higher values for the smallest ion (H + ), and decreases as the ion size enlarges (H + →Li + →Na + ), as well as the fact that D is higher for amorphous than for crystalline samples and attributed the differences to the different microstructure and composition of the thin films [70]. [52].…”

Towards enhanced durability of electrochromic WO3 interfaced with liquid or ceramic sodium-based electrolytes

“…The results are in line with the hypothesis that the diffusion coefficients are dependent of the matrix WO 3 -cases A and B-or WO 3 +NASICON -case C-and they are not correlated with the electrolyte. Moreover both D values in the configurations A and B are in the range quoted in literature [24,[51][52][53]. It is also noticeable that the determined D values for Na + cation (10 −11 to 10 −12 cm².s −1 ) are close to those reported for Li + (10 −9 to 10 −12 cm 2 .s −1 ) [24,54,55,27] or also K + (10 −11 cm 2 .s −1 ) [19], in the same WO 3 matrix.…”