Shear-driven morphotropic phase boundary in epitaxial ferroelectric thin films

We report new insights on morphotropic phase boundary (MPB) learnt from the nonlinear thermodynamics analysis of epitaxial ferroelectric films, including (1) MPB can be induced in an otherwise tetragonal ferroelectric system under a wide range of misfit shears; (2) the coexistence of tetragonal and rhombohedral phases at MPB does not necessarily lead to superior electromechanical coupling; and (3) the discontinuity in polarization across MPB is essential for the enhanced piezoelectricity. These insights point to alternative pathways to strain engineered MPB and superior electromechanical coupling that are not readily realized otherwise.