Tip-based mechanical force effects on ferroelastic twin structures in epitaxial WO$_{3}$ thin films

A-site vacant perovskite WO$_{3}$ structure varies diversely depending on the temperature due to the typical phonon modes softening, which seems to be greatly related with empty A-sites. In addition, this empty structure allows rotations of WO$_{3}$ octahedra and distortions of linear W-O-W links instantaneously by external mechanical force. In this context, reorientations of single crystal WO$_{3}$ twin domains by pressure have been reported. In this presentation, we report on changes in domain structure and instantaneous piezo-response signal changes in epitaxial WO$_{3}$ thin films induced by tip-based shear stresses. For the experiments, we synthesized high quality epitaxial WO$_{3}$ thin films on YAlO$_{3\, }$substrates and characterized its crystal structure. The WO$_{3}$ films have ferroelastic twin structures consisting of four fold monoclinc building blocks which are subject to cooperative mosaic rotations. Ferroelastic twin structures have hierarchical domains (fine-, macro-, and super-macro-domains) following power law between film thickness and domain width. We also found that the domain structure can be changed by an injection of electron beam.