Piezoelectricity Across a Strain‐Induced Isosymmetric Ferri‐to‐Ferroelectric Transition

We identify a first‐order, isosymmetric transition between a ferrielectric (FiE) and ferroelectric (FE) state in A‐site ordered LaScO₃/BiScO₃ and LaInO₃/BiInO₃ superlattices. Such a previously unreported ferroic transition is driven by the easy switching of cation displacements without changing the overall polarization direction or crystallographic symmetry. Epitaxial strains less than 2% are predicted to be sufficient to traverse the phase boundary, across which we capture a ≈5× increase in electric polarization. Unlike conventional Pb‐based perovskite ceramics with a morphotropic phase boundary (MPB) that show polarization rotation, we predict an electromechanical response up to 102 pC/N in the vicinity of the FiE‐FE phase boundary due to polarization switching without any change in symmetry. We propose this transition as an alternative ferroic transition to obtain a piezoelectric response, with the additional advantage of occurring in benign chemistries without chemical disorder.