Elastic, piezoelectric, and dielectric properties of Ba(Zr _0.2Ti_0.8)O₃-50(Ba_0.7Ca _0.3)TiO₃ Pb-free ceramic at the morphotropic phase boundary

There is an urgent demand for high performance Pb-free piezoelectrics to substitute for the current workhorse, the lead zirconate titanate (PZT) family. Recently, a triple point (also tricritical point) type morphotropic phase boundary (MPB) in Pb-free Ba(Zr_0.2Ti_0.8)O ₃-x(Ba_0.7Ca_0.3)TiO₃ system has been reported that shows equally as excellent piezoelectricity as soft PZT at room temperature (Liu and Ren). In the present study, we measured a full set of elastic, piezoelectric, and dielectric properties for the MPB composition, Ba(Zr_0.2Ti_0.8)O₃-50(Ba_0.7Ca _0.3)TiO₃ (BZT-50BCT), by using a resonance method. The resonant method gives piezoelectric properties d₃₃ = 546 pC/N, g ₃₃ = 15.3 × 10^-3 Vm/N, electromechanical coupling factor k₃₃ = 65, and the elastic constant s₃₃^E 19.7 × 10^-12 m²/N, c₃₃^E = 11.3 × 10¹⁰ N/m², which are close to the properties of soft PZT (PZT-5A). Furthermore, the piezoelectric coefficients (k₃₃, d₃₃), the ferroelectric properties (coercive field, remnant polarization), and the elastic constants (s₃₃^D, s ₃₃^E, c₃₃^D, c₃₃ ^E) were also determined as a function of temperature ranging from -50 to 60°C. Our results show that the properties are optimal around MPB temperature (room temperature) and decrease with deviations from the MPB temperature. Nevertheless, the piezoelectric coefficient d₃₃ can maintain an appreciable level of 93 pC/N even at -50°C. The high piezoelectric properties can be ascribed to the low polarization anisotropy as well as the elastic softening at MPB.