Piezoelectric properties of mechanochemically processed 0.67BiFeO₃-0.33BaTiO₃ ceramics

Solid solutions of BiFeO₃ and BaTiO₃ are promising lead-free piezoelectric materials, especially around the morphotropic phase boundary at 0.67BiFeO₃-0.33BaTiO₃. Still, these materials are challenged by phase instability and limited understanding of the processing-properties relationship. Here, we investigate mechanochemical activation and the use of BaTiO₃ as seed particles for the 0.67BiFeO₃-0.33BaTiO₃ phase. Contrary to expectations from seeding in lead-based perovskites, the BaTiO₃ seeds do not promote the 0.67BiFeO₃-0.33BaTiO₃ perovskite phase neither during the mechanochemical activation nor the subsequent sintering, but cause an inhomogeneous structure with remnant BaTiO₃. This results in ceramics with weaker low-field piezoelectric response than that of the unseeded route, but with higher field-induced strain, even up to 150 °C. Both routes produce ceramics of high density and without significant secondary phases visible by X-ray diffraction. This demonstrates the advantage of mechanochemical activation and the possibility to tailor the piezoelectric response of 0.67BiFeO₃-0.33BaTiO₃ through the processing route.