Phase structure and electromechanical response of ferroelectric thin films: a perspective on strain-orientation coupling

Ferroelectric thin films can exhibit multiple growth orientations, yet research on Ba1−xCaxTiO3 (BCT) has primarily focused on the (001)-orientation. To address this, we employ Landau-Devonshire thermodynamics, modifying the thermodynamic potential function to analyze strain-temperature phase diagrams and electromechanical coupling properties for (001)-, (110)-, and (111)-oriented BCT0.15 films. Our results show significant orientation-dependent phase variations, with symmetry progressively reducing along the (111)→(001)→(110) sequence. The electromechanical responses vary under different biaxial strains and temperatures, with dielectric and piezoelectric coefficients greatly enhanced near phase boundaries. Notably, the (111) orientation demonstrates superior electromechanical coupling over a wide strain range around room temperature.