Effect of potassium content on electrostrictive properties of Na_0.5Bi_0.5TiO₃-based relaxor ferroelectric thin films with morphotropic phase boundary

(1 − x)Na_0.5Bi_0.5TiO₃–xK_0.5Bi_0.5TiO₃ (NBT–KBT100x) (x = 0.13, 0.15, 0.18, 0.20, 0.25) thin films were prepared by metal–organic decomposition, and the crystalline structures, surface morphologies, leakage current densities and dielectric, piezoelectric, and ferroelectric properties were investigated by X-ray diffractometer, scanning electron microscopy, semiconductor characterization system, scanning probe microscopy, and ferroelectric tester, respectively. The electrostrictive equation in phenomenological theory is used to model the piezoelectric and electrostriction behaviors of relaxor ferroelectric thin films, and the electrostriction coefficient couples effective piezoelectric coefficient with the polarization and relative permittivity. The electrostriction strains are larger than the piezoelectric strains for NBT–KBT100x thin films, and the electrostriction coefficients and electrostrictive strains are at the ranges of 0.019–0.025 m⁴/C² and 0.12%–0.26%, respectively. NBT–KBT15 thin film is of the largest electrostriction coefficient and electrostrictive strain, and it is attributed to the appropriate potassium content near morphotropic phase boundary and the equivalent energy for the phase coexistence. The results indicate that NBT-based thin film with high electrostrictive properties is a promising candidate for the application in electromechanical devices. - Highlights: • Na_0.5Bi_0.5TiO₃–xK_0.5Bi_0.5TiO₃ films were prepared by metal–organic decomposition. • The electrostrictive properties were measured based on the electrostrictive equation. • Largest electrostriction coefficient and strain were 0.025 m⁴/C² and 0.26%. • Na_0.5Bi_0.5TiO₃–xK_0.5Bi_0.5TiO₃ thin films are promising for transducer applications