Simultaneous giant strain and electrostrictive coefficient in lead-free BNT-ST-BT ergodic relaxor thin films on Pt/TiO₂/SiO₂/Si substrates

The acquisition of hysteresis-free and large electrostrain in lead-free piezoelectric thin films is the key issue for the development of high-performance micro actuators. The electrostrictive effect is an appropriate choice for developing hysteresis-free electrostrain. Lead-free ferroelectric compound Bi_1/2Na_1/2TiO₃ has great potential in realizing large electrostrain response and electrostrictive coefficient. In this work, (0.8-x)Bi_1/2Na_1/2TiO₃-0.2SrTiO₃-xBaTiO₃ (BNT-ST-100xBT) thin films were prepared by chemical solution deposition method. The crystal structure, morphology, dielectric properties, electrostrictive effect, dielectric nonlinearity, ferroelectric properties, and electrostrain response were systematically investigated. The most significant electrostrictive effect was obtained in the ergodic relaxor BNT-ST-6BT thin film, i.e., a giant electrostrictive coefficient of 0.21 m⁴/C². Meanwhile, by increasing the applied electric field, a linearly increasing strain and the maximum value of 0.82 % were obtained in this film. This work has made an important step in the electrostrictive effect study and provides a pathway to obtain hysteresis-free electrostrain in lead-free perovskite ferroelectric thin films.