In a series of Cs-doped tungsten oxides that underwent different degrees of reduction, new components and behaviors were found in X-ray photoelectron spectroscopy (XPS) signals of O−1s, W−4f, and Cs−3d and analyzed in terms of oxygen vacancies (V O s) and electron localization with the aid of first-principles calculations. Orthorhombic Cs 4 W 11 O 35 was reduced at high temperature to transform it to hexagonal tungsten bronze with increasing W 5+ trapped electrons, as detected in W−4f. The binding energy of W 5+ −4f showed a distinct redshift toward low saturation values that was implied to be due to W 5+ alignment on the hexagonal prismatic planes. The V O enthalpy of formation and the Bader charge calculated for each atom site supported this view, by identifying the preferred sites for V O and W 5+ on (020) in Cs 4 W 11 O 35 . The W 5+ component was newly admitted in O−1s at 531.25−531.94 eV and 532.35−533.04 eV, while the carbonation contributions were eliminated using C−1s deconvolution. In Cs−3d, a V O -related extra component was found on the high-energy side, which grew with increasing reduction time. These observations and calculations supported the proposition that electrons emitted from Cs should be delocalized, and those from V O s should be both localized and delocalized in Cs-doped tungsten oxides.
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