Thickness-dependent dielectric nonlinear properties of 0.78Bi0.5Na0.5TiO3–0.2SrTiO3–0.02BaTiO3 thin films in a thickness range of 0.62–1.62 μm were investigated in this work. It was demonstrated that the dielectric properties decreased with the decrease in thickness due to the substrate clamping inducing the degeneration of intrinsic contribution and the reduced domain wall mobility. A low DC electric field promoted domain switching and reversible domain wall motion. The domain mobility was suppressed by a high DC electric field, which resulted in reduced dielectric permittivity combined with the tunability of intrinsic dielectric response.

In recent years, the development of environmentally friendly, lead-free ferroelectric films with prominent electrostrictive effects have been a key area of focus due to their potential applications in micro-actuators, sensors, and transducers for advanced microelectromechanical systems (MEMS). This work investigated the enhanced electrostrictive effect in lead-free sodium bismuth titanate-based relaxor ferroelectric films. The films, composed of (Bi_0.5Na_0.5)_0.8−xBa_xSr_0.2TiO₃ (BNBST, x = 0.02, 0.06, and 0.11), with thickness around 1 μm, were prepared using a sol-gel method on Pt/TiO₂/SiO₂/Si substrates. By varying the Ba²⁺ content, the crystal structure, morphology, and electrical properties, including dielectric, ferroelectric, strain, and electromechanical performance, were investigated. The films exhibited a single pseudocubic structure without preferred orientation. A remarkable strain response (S > 0.24%) was obtained in the films (x = 0.02, 0.06) with the coexistence of nonergodic and ergodic relaxor phases. Further, in the x = 0.11 thick films with an ergodic relaxor state, an ultrahigh electrostrictive coefficient Q of 0.32 m⁴/C² was achieved. These findings highlight the potential of BNBST films as high-performance, environmentally friendly electrostrictive films for advanced microelectromechanical systems (MEMS) and electronic devices.