Constructing Morphotropic Phase Boundary in Epitaxial BiFeO3 on SrTiO3 by Suppression of Strain Relaxation

The strain-driven morphotropic boundary in BiFeO3 can enhance the piezoelectric properties. However, the tetragonal phase has generally been observed in BiFeO3 films grown on substrates with intense compressive strain (more than −4.5%) within a limited thickness range (3 films decreases to 200 °C. As a result, the tetragonal phase is observed in 600-nm-thick BiFeO3 film on (001) SrTiO3 substrates (strain equals only −1.5%), accompanied by the monoclinic phase. This SrTiO3-available morphotropic phase boundary significantly enhances the piezoelectric response (Formula presented.) in epitaxial BiFeO3 film. Ex situ and in situ measurements, theoretical calculations, and simulation confirm that the SrTiO3-available morphotropic phase boundary originates from the suppressed strain relaxation. Furthermore, a critical temperature (400 °C), below which the tetragonal phase can be maintained, is identified to offer an applicable strategy for extending strain-driven morphotropic phase boundary for high-performance piezoelectric films. © 2024 Wiley-VCH GmbH.