Huge strain and energy storage density of A-site La³⁺ donor doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics

Lead-free ferroelectric [(Bi_0.5Na_0.5)_0.94Ba_0.06]_1−xLa_xTiO₃ (BNBT-100xLa, 0≤x≤0.05) ceramics were prepared by the solid state sintering methods and the effects of La³⁺ doping on ferroelectricity and electromechanical strain were systematically investigated. The X-ray diffraction analysis revealed that the crystal structure partly transformed from rhombohedral phase to tetragonal phase with the increasing of La³⁺ donor doping. The long-range FE order dominant in pure BNBT was disrupted by La³⁺ doping. For BNBT-3La, the largest maximum strain S_max was 0.53% with a high normalized strain d^*₃₃ of 707 pm/V under 75 kV/cm at room temperature. Moreover, a phase transition happened at E_F=46.06 kV/cm under the cycle of 75 kV/cm. In particularly, a slim and pinched P-E loop was obtained for BNBT-5La with a large energy density of 1.66 J/cm³ at 105 kV/cm.