Uniaxial Strain‐Driven Ferroelastic Domain Tuning in LaAlO3

Multiferroic domain walls in functional oxides exhibit properties distinct from the bulk and are increasingly exploited as active elements in nanoelectronic and photonic devices. Deterministic tuning of domain populations has typically remained limited to local solutions, or removal with temperature. Here, the manipulation of ferroelastic domain structure, and removal of the twin walls between them in single‐crystal using in situ uniaxial strain is demonstrated. Combining atomic force microscopy, X‐ray diffraction, and Raman spectroscopy with first‐principles calculations, the microscopic evolution of the twin domain population is mapped through a strain‐driven transition from the rhombohedral ground state toward the predicted orthorhombic phase. Applied strains below produce pronounced surface flattening and large‐scale domain reorganization, establishing uniaxial strain as a technically accessible tuning parameter for ferroelastic domain engineering. These results open a route to active alterations of domain architectures in ‐based heterostructures, with implications for epitaxial film properties, nanoscale phonon‐polariton optics, and ultrafast lattice control.