Defect-Mediated Growth of Crystallographic Shear Plane

As representative extended planar defects, crystallographic shear (CS) planes, namely Wadsley defects, play an important role in modifying the physical and chemical properties of metal oxides. Although these special structures have been intensively investigated for high-rate anode materials and catalysts, it is still experimentally unclear how the CS planes form and propagate at the atomic scale. Here, the CS plane evolution in monoclinic WO3 is directly imaged via in situ scanning transmission electron microscope. It is found that the CS planes nucleate preferentially at the edge step defects and proceed by the cooperative migration of WO6 octahedrons along particular crystallographic orientations, passing through a series of intermediate states. The local reconstruction of atomic columns tends to form (102) CS planes featured with four edge-sharing octahedrons in preference to the (103) planes, which matches well with the theoretical calculations. Associated with the structure evolution, the sample undergoes a semiconductor-to-metal transition. In addition, the controlled growth of CS planes and V-shaped CS structures can be achieved by artificial defects for the first time. These findings enable an atomic-scale understanding of CS structure evolution dynamics.

Automated summary

The evolution of crystallographic shear (CS) planes in monoclinic WO3 was directly observed using in situ scanning transmission electron microscopy. The CS planes were found to nucleate preferentially at edge step defects and propagate through a cooperative migration of WO6 octahedrons along specific crystallographic orientations. The local reconstruction of atomic columns favored the formation of (102) CS planes with four edge-sharing octahedrons over (103) planes, in agreement with theoretical calculations. The structure evolution was accompanied by a semiconductor-to-metal transition. Furthermore, controlled growth of CS planes and V-shaped CS structures was achieved for the first time using artificial defects. These findings provide an atomic-scale understanding of CS structure evolution dynamics.