The elastic, piezoelectric, and dielectric constants of $\text{0.67}{\mathrm{Pb(Mg}}_{\mathrm{1/3}}{\mathrm{Nb}}_{\mathrm{2/3}}{\mathrm{)O}}_{\mathrm{3}}{\mathrm{–0.33PbTiO}}_3$ domain engineered single crystal were determined experimentally by using ultrasonic and resonance methods. It was confirmed that the single crystal system has large electromechanical coupling coefficient $k_{33}$ (∼94%) and piezoelectric constant $d_{33}$ (∼2800 pC/N) if the poling is done along the [001] of pseudocubic directions. A soft shear mode with a velocity of 880 m/s was observed in the [110] direction with displacement in $\text{[1̄10].}$ Using the measured data, the orientation dependence of phase velocities and electromechanical coupling coefficients were calculated. The origin of experimental errors and their influence on measured results are also examined.

Commercial lead-based piezoelectric materials raised worldwide environmental concerns in the past decade. Bi_0.5Na_0.5TiO₃-based solid solution is among the most promising lead-free piezoelectric candidates; however, depolarization of these solid solutions is a longstanding obstacle for their practical applications. Here we use a strategy to defer the thermal depolarization, even render depolarization-free Bi_0.5Na_0.5TiO₃-based 0–3-type composites. This is achieved by introducing semiconducting ZnO particles into the relaxor ferroelectric 0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃ matrix. The depolarization temperature increases with increasing ZnO concentration until depolarization disappears at 30 mol% ZnO. The semiconducting nature of ZnO provides charges to partially compensate the ferroelectric depolarization field. These results not only pave the way for applications of Bi_0.5Na_0.5TiO₃-based piezoceramics, but also have great impact on the understanding of the mechanism of depolarization so as to provide a new design to optimize the performance of lead-free piezoelectrics.