Crystal Structure, dielectric and ferroelectric properties of (Bi_0.5Na_0.5)TiO₃-(Ba,Sr)TiO₃ lead-free piezoelectric ceramics

The crystal structure, microstructure, dielectric and ferroelectric properties of (1 - x)(Bi_0.5Na_0.5)TiO₃-x(Ba_0.7Sr_0.3)TiO₃ (BNBST30-x, x = 0-0.12) lead-free piezoelectric ceramics were studied in this work. Structural variation according to (BNBST30-x) composition was carefully investigated by X-ray diffraction analyses. A rhombohedral-tetragonal morphotropic phase boundary (MPB) is found at BNBST30-8 composition which shows the highest remanent polarization value. Smallest coercive field value is observed at the tetragonal-side of MPB, i.e. BNBST30-10, instead of MPB composition. The addition of Sr²⁺ ions plays a role as soft dopant on the dielectric properties in the present BNBST systems. In comparison with the MPB compositions containing various Sr²⁺ ratios, the dielectric and piezoelectric properties (ε₃₃^T/e₀ and d₃₃) are effectively enhanced when Sr²⁺ ratio is higher. Besides, Sr²⁺ allows to enlarge the cell volume that is also advantageous for the improvement of dielectric and piezoelectric performances.