Giant strain responses and relaxor characteristics in lead-free (Bi_0.5Na_0.5)TiO₃-BaZrO₃ ferroelectric thin films

Lead-free bismuth sodium titanite, (Bi_0.5Na_0.5)TiO₃ (BNT)-based piezoelectric thin films have enormous potential in applications such as micro-actuators and micro-ultrasonic transducers due to their large strain responses. In this paper, (1 − x)(Bi_0.5Na_0.5)TiO₃-xBaZrO₃ (x = 0.02, 0.04, 0.06 and 0.07, BNT-100xBZ) piezoelectric thin films were deposited on Pt/TiO₂/SiO₂/Si (001) substrates by sol-gel method. All BNT-100xBZ thin films showed good macro-morphology and crystallinity. In addition, no clear phase structure transition was observed by increasing the BZ contents in the BNT-100xBZ solution, which, however, leads to evident variations in the dielectric and piezoelectric properties of the BNT-100xBZ thin films. A giant macro-scale strain value of 1.31% was obtained in the BNT-4BZ thin films, accompanied by a relatively lower dielectric loss of 0.03 for all BNT-100xBZ thin films. According to temperature- and frequency-dependent dielectric properties, it is found that the BNT-4BZ composition has a coexistence of ferroelectric phase and relaxor characteristics, which is different from other compositions. Furthermore, the intensity of the current peak related to the domain switching in the BNT-4BZ thin films is higher than that of other compositions. This work is of great interest for further enhancement of the strain response and reduction of the dielectric loss in BNT-based lead-free thin films for various piezoelectric device applications like micro-actuator systems.