A Strain-Driven Morphotropic Phase Boundary in BiFeO ₃

TLDR

Piezoelectric materials rely on the coexistence of two phases at a morphotropic phase boundary, enabling large electromechanical coupling, and there is a strong push to develop practical lead‑free piezoelectrics. The authors employ epitaxial growth and theoretical modeling to induce a morphotropic phase boundary in lead‑free BiFeO₃ films via epitaxial constraint. Field‑dependent measurements reveal reversible tetragonal‑to‑rhombohedral phase switching with surface displacement, indicating potential for probe‑based data storage and actuator use.

Abstract

Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.