Strain-Induced Antiferroelectric-Ferroelectric-Antiferroelectric Phase Transitions in Epitaxial LaTaO₄ Films

We employed first-principles to delve into the strain-induced structural phase transitions in epitaxial LaTaO₄ films. The ground state of bulk LaTaO₄ adopts a monoclinic antiferroelectric phase, characterized by the antiphase rotation of two adjacent oxygen octahedra layers. Under epitaxial tensile strain, LaTaO₄ thin films undergo a consecutive phase transition, namely, antiferroelectric-ferroelectric-antiferroelectric phase transitions. The ferroelectricity in the orthorhombic phase under tensile strain originates from the in-phase rotation of two adjacent oxygen octahedra layers, in contrast to the case of perovskite systems, in which octahedra rotation suppresses the conventional proper ferroelectricity. With spin-orbit coupling effects, a pronounced Rashba effect at the Brillouin zone center naturally leads to the formation of opposite directions of spin texture. Moreover, the tensile strain also synergistically enhances the corresponding Rashba parameters. Our findings may provide novel insights for controlling oxygen octahedra rotation to achieve control over the ferroelectricity and Rashba effect, which holds promising implications for applications in electronics and spintronics.