Relationship between electromechanical properties and phase diagram in the Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 lead-free piezoceramic

The Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 system was synthesized in a wide compositional range in order to study the relationship between its phase diagram and electromechanical properties. Phase transitions were marked using peaks in temperature-dependent permittivity, providing up to three transitions from the rhombohedral phase to an orthorhombic, tetragonal and finally cubic phase, which meet in a region that is termed the phase convergence region in this work. In situ small and large signal electromechanical properties were studied as a function of temperature with specific emphasis on these transitions. A small signal piezoelectric coefficient, d33, presents maximized values at the transition from the orthorhombic to the tetragonal phase, while a large signal piezoelectric coefficient, d33∗, does so at both rhombohedral to orthorhombic and to tetragonal phase transitions. Maximum polarization Pmax was the only quantity determined that had a clear maximum at the phase convergence region.