Lattice distortion induced by rare-earth ions doping in (Bi_0.5Na_0.5)TiO₃-based thin films with high piezoelectric properties

High-performance lead-free piezoelectric thin films are urgently required for microelectromechanical systems. In this study, thin films based on the 0.8Bi(0.5)Na(0.5)TiO(3)-0.2(Sr0.7Bi0.2 square(0.1))TiO3 system were prepared on Pt(111)/TiOx/SiO2/Si substrates by a sol-gel method. The large lattice distortions were induced by introducing five rare-earth ions with different ionic radii (Er/Pr/Sm/Nd/La) to achieve the purpose of regulating the piezoelectric response of the thin films with the maximum inverse piezoelectric coefficient up to 425.9 pm/V. X-ray diffraction, Raman spectroscopy, Piezoresponse force microscope, and additional testing methods were used to observe the phase composition and microstructure of the thin films to investigate the effect of doping rare-earth elements with different ionic radii at the A-site on lattice distortion, and to summarize the transformation law. This study is significant for improving the piezoelectric properties of thin films and has crucial applications in microelectronic sensing.