Crystal Structure and ferroelectric properties of (Bi_0.5Na _0.5)TiO₃-Ba(Zr_0.05Ti_0.95)O ₃ piezoelectric ceramics

The crystal structure and ferroelectric properties of (1-x)(Bi _0.5Na_0.5)TiO₃-xBa(Zr_0.05Ti _0.95)O₃ (BNBZTx, x≤12%) lead-free piezoelectric ceramics were studied. The distance between the centers of cations and anions (d_c-a) as well as the lattice parameters was carefully investigated by Rietveld refinement on X-ray diffraction patterns. It was found that the crystal phase was determined by the amount of Ba(Zr_0.05Ti _0.95)O₃ added, whereas the pure rhombohedral and tetragonal phases are observed in compositions containing x≤4 and x≥8%, respectively. A rhombohedral-tetragonal morphotropic phase boundary (MPB) was found at around BNBZT6, which showed a maximum and minimum d_c-a at its rhombohedral and tetragonal phases, respectively. According to the present study, the ferroelectric properties show a strong dependence on their crystal phases. For the single-phase compositions, the remanent polarization (P _r) generally increased with the value of d_c-a while their coercive fields (E_c) were determined by their lattice parameters. Nevertheless, the behavior in P_r and E_c for MPB compositions is related to not only the lattice parameter but also the composed phases.