Composition-electric field phase diagram of the Pb-free piezoelectric system Na_0.5Bi_0.5TiO₃-BaTiO₃

(1-x)Na0.5Bi0.5TiO3-BaTiO3 is one of the important Pb-free piezoelectric alloy systems. Despite extensive investigation over the years, the composition x-electric field (E) phase diagram of this alloy system has not received sufficient attention. Here, we performed an x-ray diffraction study in situ with electric fields at close composition intervals in a wide range: 0.0 <= x <= 0.18. We discovered that this system exhibits field-driven, reversible interferroelectric transformations ina large composition range: 0.02 < x < 0.14. Based on this work, we present the first comprehensive x-E phase diagram of this system. Apart from addressing inconsistencies in an earlier study, our phase diagram can precisely explain the composition trend of both the weak-field (dielectric and piezoelectric) and high-field (electrostrain) properties of this Pb-free piezoelectric system.