Large strain response in acceptor- and donor-doped Bi_0.5Na_0.5TiO₃-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi0.5Na0.5TiO3-Bi0.5Li0.5TiO3-BaTiO3-Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Qm) ~ 160, coercive field (Ec) ~ 2.9 kV/mm, decreased dielectric constant (ε33{T/ε0)∼ 803, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d33) ~ 184 pC/N, ε33T/ε0∼ 983, tanδ ~ 0.033, and decreased Ec~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature Td, large strain value was obtained with the normalized d33* up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.