Structure–property relationships in electrochromic WO 3 films deposited by reactive sputtering

Abstract

WO x electrochromic (EC) films deposited by DC magnetron sputtering technique were investigated by XRD and STM measurements. The reversible microstructure changes of the WO x film between the bleached and colored EC states were revealed. The study indicates that the amorphous as-deposited WO x film (a-WO x ) is of amorphous microstructure both in bleached and colored states; however, the crystalline WO x (c-WO x ) is stoichiometric triclinic lattice WO 3 in bleached state (the lattice parameters: a=7.2944 Å, b=7.4855 Å, c=3.7958 Å, α=89.38°, β=90.42°, γ=90.80°), and changes into nonstoichiometric tetragonal lattice WO 2.9 in colored state ( a= b=5.336 Å, c=3.788 Å, α= β= γ=90°). The surface morphologies of the colored WO x films are very different from those of the bleached WO x films.