Ferroelectric, elastic, piezoelectric, and dielectric properties of Ba(Ti_0.7Zr_0.3)O₃-x (Ba_0.82Ca_0.18)TiO₃ Pb-free ceramics

We designed and synthesized a pseudo-binary Pb-free system, Ba(Ti_0.7Zr_0.3)O₃-x(Ba_0.82Ca_0.18)TiO₃, by combining a rhombohedral end (with only cubic to rhombohedral ferroelectric phase transition) and a tetragonal end (with only cubic to tetragonal ferroelectric phase transition). The established composition-temperature phase diagram is characterized by a tricritical point type morphotropic phase boundary (MPB), and the MPB composition has better ferroelectric, piezoelectric, and dielectric properties than the compositions deviating from MPB. Moreover, a full set of material constants (including elastic stiffness constants, elastic compliance constants, piezoelectric constants, dielectric constants, and electromechanical coupling factors) of the MPB composition are determined using a resonance method. The good piezoelectric performance of the MPB composition can be ascribed to the high dielectric constants, elastic softening, and large electromechanical coupling factor.