FISMAT: XAS and RIXS investigation of oxygen vacancy engineering in WO3-x films: from amorphous to crystalline phases
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Quantitative non-negative matrix factorization (NNMF) analysis of RIXS datasets resolves mixed-valence tungsten states (W⁴⁺, W⁵⁺, W⁶⁺) in WO3-x, enabling extraction of the previously obscured W⁵⁺ component. The results show that W⁴⁺-rich configurations dominate optical absorption and electrical conduction, with infrared response consistent with small-polaron hopping between mixed-valence sites in amorphous WO3-x.