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 electrome-chanical properties of differently oriented K 0 . 5 Na 0 . 5 NbO 3 thin films. It is revealed that notable distinctions in the phase structure of K 0 . 5 Na 0 . 5 NbO 3 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 . 5 Na 0 . 5 NbO 3 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 . 5 Na 0 . 5 NbO 3 thin films outperform (111) oriented K 0 . 5 Na 0 . 5 NbO 3 thin films in terms of dielectric properties, featuring a dielectric constant exceeding 2500. Furthermore, (001) oriented K 0 . 5 Na 0 . 5 NbO 3 thin films exhibit superior out-of-plane piezoelectric properties compared to other orientations, with a remarkable piezoelectric coefficient d 33 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.