Phase Structures and Electromechanical Properties of Differently Oriented Epitaxial K_0.5Na_0.5NbO₃ Thin Films

Abstract

An evolved nonlinear thermodynamic theory is used to investigate the phase structures and electromechanical properties of differently oriented K0.5Na0.5NbO3 thin films. It is revealed that notable distinctions in the phase structure of K0.5Na0.5NbO3 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 K0.5Na0.5NbO3 thin films exhibit commendable out-of-plane dielectric and piezoelectric properties around the specific phase boundaries, such as Maac-Oaa and Tec-PE phase boundaries for (001) oriented films, Maac-Oaa and Tec-PE phase boundaries for (110) oriented films, Raaa-PE phase boundary for (111) oriented films. Specifically, near room temperature, the (001) and (110) oriented K0.5Na0.5NbO3 thin films outperform (111) oriented K0.5Na0.5NbO3 thin films in terms of dielectric properties, featuring a dielectric constant exceeding 2500. Furthermore, (001) oriented K0.5Na0.5NbO3 thin films exhibit superior out-ofplane 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.