Small polaron formation in porous WO3−x nanoparticle films

Abstract

Porous tungsten oxide nanoparticle films were prepared by reactive gas evaporation. The structure was studied by x-ray diffraction and scanning electron microscopy, and the oxygen nonstoichiometry was inferred by x-ray photoelectron spectroscopy, elastic recoil detection analysis, and neutron scattering. Specifically, the films consisted of WO3−x with 0.25<x<0.4. The optical and electrical data were consistent with the formation of small polarons having a radius of 5–6Å. The infrared optical data, used to extract information on phonon energies, were instrumental to reach this conclusion. The polaron hopping energy was about half the polaron binding energy, as expected from the theory.

Polaron and phonon properties in proton intercalated amorphous tungsten oxide thin films

“…5,31,32,57 However, many authors indicated that a single Gaussian line shape cannot completely account for the optical properties of colored WO 3 . 33,55,58,59 Our analysis reveals that the polaron-induced DF changes in colored amorphous tungsten oxide films is excellently characterized for charge densities between x = 0 , . .…”

“…2,32,56,57 It has already been observed that a single Gaussian or Lorentzian line shape is not fully sufficient to describe the experimentally observed absorption behavior. 33,55,58,59 Here we obtain that polaron-induced DF changes in colored tungsten oxide film must be modeled by two separate oscillators with Lorentzian and Gaussian line shapes. We identify these oscillators with the transitions between W 4+ and W 5+ and between W 5+ and W 6+ states, respectively, as described below.…”

Low-temperature synthesis and electrical transport properties of W18O49 nanowires

“…The electrical transport properties of W 18 O 49 are believed to be dominated by the formation and hopping of small polarons [23,24]. In unpolar materials, such as germanium, the distortion of the lattice round a charged center is usually neglected when the electrons transport through them.…”

Electrochemical measurements of the electronic density of states

“…The potential of the amorphous sample decreases smoothly as x increases, although one may note some broad structures in the curve. The nanocrystalline sample (grain size ~5 nm) [17] shows an intermediate behavior. The features are broader than for the polycrystalline sample, but the structure around x~0.3 is close to one of the plateaus in the crystalline data.…”