d orbital research in epitaxial {103} crystallographic shear phase WO3-x thin film

In transition metal oxides, the connectivity of MO6 octahedra governs the crystal structure and strongly influences the electronic states. Modulation of this connectivity alters the d orbital configuration and determines the material’s physical properties. Partial modulation can induce d orbital localization, giving rise to unique functionalities. A representative case is the crystallographic shear (CS) phase, where corner sharing octahedral blocks are periodically linked by additional sharing planes. Within these CS planes, d orbitals become spatially localized, which is considered the origin of their unconventional properties. However, direct observation of such localized states has been limited by difficulty of synthesizing single-crystalline CS phases formed through planar oxygen-vacancy ordering.

 In this study, we epitaxially fabricated a {103} CS phase tungsten suboxide thin film by inducing ordered oxygen vacancy planes under controlled strain. Transmission electron microscopy and x-ray diffraction confirmed the atomic arrangement and periodic CS plane ordering. W L1 edge XANES revealed higher symmetry octahedral features compared with monoclinic WO3 film. W L3 edge resonant inelastic x-ray scattering directly evidenced the localized d electron states within the CS planes.