Semiconductor/relaxor 0-3 type composites without thermal depolarization in Bi₀.₅Na₀.₅TiO₃-based lead-free piezoceramics.

Commercial lead-based piezoelectric materials raised worldwide environmental concerns in the past decade. Bi₀.₅Na₀.₅TiO₃-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 Bi₀.₅Na₀.₅TiO₃-based 0-3-type composites. This is achieved by introducing semiconducting ZnO particles into the relaxor ferroelectric 0.94Bi₀.₅Na₀.₅TiO₃-0.06BaTiO₃ 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 Bi₀.₅Na₀.₅TiO₃-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.