Landau-Devonshire theory-based phase diagram of the bismuth ferrite and barium titanate solid solution

Abstract

The development of high-performance, lead-free piezoelectric ceramics is essential for modern sensor and actuator applications. Bismuth ferrite-based solid solutions, like (1-x)BiFeO₃-xBaTiO₃ (BF-BT), are promising due to their high Curie temperature and high piezoelectric performance, but ambiguities persist regarding their phase transitions and the exact location of the morphotropic phase boundary (MPB), where piezoelectric properties are maximized. This study resolves these issues by applying Landau-Devonshire theory to construct a comprehensive phase diagram for the BF-BT system. By calculating the free energy density landscape, our theoretical model accurately reproduces the material's composition-dependent properties. The resulting phase diagram agrees well with experimental observations, predicting a coexistence of rhombohedral and tetragonal phases near x = 0.33. And our calculations identify the MPB at a composition of x = 0.375, consistent with the experimentally reported range. These findings highlight the link between phase structure and piezoelectric performance.