Phase Structures and Electromechanical Properties of Differently Oriented Epitaxial K0.5Na0.5NbO3 Thin Films

Abstract

An evolved nonlinear thermodynamic theory is used to investigate the phase structures and electromechanical properties of differently oriented K_0.5Na_0.5NbO₃ thin films. It is revealed that notable distinctions in the phase structure of K_0.5Na_0.5NbO₃ thin films, with decreasing symmetry observed in the order of (111), (001), and (110) orientations, and these microphase structural variances translate into distinct electromechanical properties. Moreover, it is observed that the oriented K_0.5Na_0.5NbO₃ thin films exhibit commendable out-of-plane dielectric and piezoelectric properties around the specific phase boundaries, such as M_aac–O_aa and Te_c–PE phase boundaries for (001) oriented films, M_aac–O_aa and Te_c–PE phase boundaries for (110) oriented films, R_aaa–PE phase boundary for (111) oriented films. Specifically, near room temperature, the (001) and (110) oriented K_0.5Na_0.5NbO₃ thin films outperform (111) oriented K_0.5Na_0.5NbO₃ thin films in terms of dielectric properties, featuring a dielectric constant exceeding 2500. Furthermore, (001) oriented K_0.5Na_0.5NbO₃ thin films exhibit superior out-of-plane piezoelectric properties compared to other orientations, with a remarkable piezoelectric coefficient d₃₃ exceeding 1000 pm/V. These results underscore the significant impact of strain and temperature regulation on electromechanical properties. Meanwhile,  by  strategically  adjusting these parameters, it becomes feasible to fabricate high-properties piezoelectric devices.