Ultra-high strain responses in lead-free (Bi_0.5Na_0.5)TiO₃-BaTiO₃-NaNb O₃ ferroelectric thin films

Lead-free (Bi0.5Na0.5)TiO3 (BNT)-based piezoelectric materials, have a great potential for high-precision actuators' applications. In this work, the high-quality (0.94-x%)(Bi0.5Na0.5)TiO3-0.06BaTiO3-x%NaNbO3 (x = 2-10, BNT-6BT-xNN) thin films have been successfully deposited on Pt/TiO2/SiO2/Si substrates by sol-gel method. An ultra-high poling strain Spol value of 1.7% with a unipolar strain Suni value of 1.47% was reported in the BNT6BT-6NN thin films. The coexistence of the ferroelectric phase and relaxor state was observed in the compositions of x = 2-8. Furthermore, the BNT-6BT-6NN thin films show more active domain switching compared to other compositions. It is demonstrated that the optimized strain responses in the BNT-6BT-6NN are attributed to a synergistic reaction of active domain switching and reversible electric-field-induced phase transition between the ferroelectric phase and relaxor state. Our systematic study demonstrates that the BNT-6BT-xNN thin films with an improved strain response are promising candidates for the applications of miniaturized actuators.