Atomic‐Scale Origin and Reconstruction Pathways of Block Defects in Nb 16 W 5 O 55 Wadsley–Roth Shear Oxides

ABSTRACT Wadsley–Roth shear oxides in Nb 16 W 5 O 55 have attracted increasing interest for open crystallographic tunnels and structurally robust block frameworks. However, the actual crystal structure often deviates from the ideal (4 × 5) block arrangement, and the origin and nature of these deviations remain unclear. Defect structures in Nb 16 W 5 O 55 single crystals are directly visualized with atomic‐resolution high‐angle annular dark‐field scanning transmission electron microscopy, and the coexistence of (4 × 5) and W‐deficient (4 × 4) MO 6 octahedral blocks is revealed. Two block types share a compatible interface defined by MO 4 tetrahedra and MO 6 octahedra; they readily join to form extended linear defects that span entire particles. Furthermore, the bidirectional attachment of (4 × 5) blocks to the two facets of (4 × 4) blocks generates rare cross‐type (5 × 5) defects accompanied by significant local strain. These findings provide direct atomic‐level insight into real structural complexity in Nb 16 W 5 O 55 shear phases.