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 Bi_0.5Na_0.5TiO₃–Bi_0.5Li_0.5TiO₃–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 (Q_m) ~ 160, coercive field (E_c) ~ 2.9 kV/mm, decreased dielectric constant \( \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, \) and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d₃₃) ~ 184 pC/N, \( \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, \) tanδ ~ 0.033, and decreased E_c ~ 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 T_d, large strain value was obtained with the normalized \( d_{33}^{*} \) 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.