In Situ Observations of Ferroelastic Domain Evolution in Epitaxial WO₃ Films.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Ferroelastic materials exhibit reversible phase transitions and mechanical hysteresis, making them promising for strain-engineered applications.
• Tungsten trioxide (WO3) is a model ferroelastic system, but its domain evolution mechanisms in thin films under thermal stress are not fully understood.

Purpose of the Study:

• To investigate the mechanisms governing ferroelastic domain evolution in tungsten trioxide (WO3) thin films.
• To elucidate the roles of epitaxial strain and thermal activation in mediating functional oxide phases.

Main Methods:

• Fabrication of WO3 films on LaAlO3 substrates using pulsed laser deposition.
• Characterization via high-resolution scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD).
• In situ transmission electron microscopy (TEM) and in situ X-ray reciprocal space mapping to observe domain evolution.

Main Results:

• Confirmed coherent epitaxial growth and hierarchical ferroelastic twins with labyrinthine domain structures in WO3 films.
• Elucidated thermally driven domain evolution from b-domain to a- or c-domain configurations.
• Identified giant strain gradients in domain walls, suggesting potential flexoelectric effects.

Conclusions:

• The study uncovers key mechanisms of ferroelastic domain evolution in WO3 thin films.
• Epitaxial strain and thermal activation are critical factors in controlling ferroelastic domain behavior and functional oxide phases.
• Provides fundamental insights for strain-mediated manipulation of ferroelastic domains in oxide materials.