Abstract:

Piezoelectric actuators have advantages of fast response, high positioning accuracy, small size, and have received widespread attention in the field of precision drives. Lead-based piezoelectric actuators occupy the main commercial market. To avoid the use of the harmful element lead, a lead-free piezoelectric materials and actuators must be developed. Among them, bismuth sodium titanate (Bi_0.5Na_0.5)TiO₃ (BNT), was reported but it has some disadvantages of higher driving voltage, larger hysteresis, and poor temperature stability. To optimize the strain performance of the lead-free actuator, this study adopted the solid-phase reaction method to prepare (1-x) {0.76(Bi_0.5Na_0.5)TiO₃- 0.24SrTiO₃}-xNaNbO₃ (BNT-ST-xNN, x=0-0.03) lead-free ferroelectric ceramics, systematically studied its field- induced strain performance. The results show that when x=0.01, the strain value of the ceramic can reach 0.278% under a low electric field (E = 4 kV/mm), and the piezoelectric coefficient d^*₃₃ is as high as 695 pm/V. Meanwhile, the ceramic is at the non-ergodic/ergodic relaxation phase boundary, and the electric field induced relaxor-ferroelectric phase transition leads to large field-induced strain. Compared with x=0.01, the strain value at x=0.02 is 0.249%, which is slightly reduced, but the hysteresis is significantly reduced to 43% of the comparator. In addition, the strain remains stable in the temperature range of 25-100 ℃. This study shows that introduction of SrTiO₃ and NaNbO₃ into BNT can increase the field-induced strain value while maintaining a low driving voltage and good temperature stability, indicating suitable for the development of piezoelectric actuators.

Key words: sodium bismuth titanate, lead-free ferroelectric ceramics, field-induced strain, relaxed state