Morphotropic Phase Boundary Slope of (K,Na,Li)NbO3–BaZrO3 Binary System Adjusted Using Third Component (Bi,Na)TiO3 Additive

In the binary composition-temperature phase diagram, the slope of the phase boundary is related to the temperature stability of the phases and/or properties. The slope of the tetragonal–rhombohedral morphotropic phase boundary (MPB) in the BaZrO3–(K,Na,Li)NbO3 (BZ–KNLN) binary system has been adjusted using the third component (Bi,Na)TiO3 (BNT). Piezoceramics were synthesized by a conventional solid-state reaction method, and their crystal structures as well as their MPB were determined from X-ray diffraction patterns measured from room temperature to 300 °C. With increasing BNT content, the slope of the MPB changed from negative to positive. An MPB with temperature-independent behavior, the so called vertical MPB, was successfully discovered in this lead-free piezoceramic system. The MPB composition was determined to be 0.075BZ–0.915KNLN–0.01BNT and the Curie temperature was found to be about 270 °C. The results obtained in this work could be used to develop high-performance lead-free piezoceramics compatible with lead-based ones. Furthermore, this is the first time a vertical MPB has been artificially formed by adjusting the MPB slope. The research method presented in this work has important practical implications as well as scientific interest for searching for vertical MPBs in lead-free piezoceramic systems.