The improvement of piezoelectric properties in BiFeO₃–BaTiO₃ lead-free ceramics prepared with heat-treated rutile TiO₂

BiFeO₃–BaTiO₃ lead-free piezoelectric ceramics have been studied for their application to sensors and actuators. The high strain and piezoelectric actuator coefficient (d₃₃*) are observed in tetragonal 0.60BiFeO₃–0.40BaTiO₃ ceramic with heat-treated single-phase rutile titanium dioxide (TiO₂) powders than in ceramic with commercial mixed-phase with rutile and anatase TiO₂. The optimized sintering temperature is 1010 °C with the quenching process. The increase of the grain size in microstructure, higher tetragonal phase volume fraction, and higher tetragonality are observed in ceramic with rutile TiO₂ than in ceramic with commercial TiO₂. The maximum strain is 0.316%, and d₃₃* is 576 pm/V. A high Curie phase transition temperature of 355 °C is measured with the maximum dielectric constant (ε_r,_max) about 30% higher than that of ceramic with commercial TiO₂. It is found that the single-phase starting material is important to improve piezoelectric, ferroelectric, and dielectric properties in lead-free piezoelectric ceramics.