Preparation of {001}_c-oriented epitaxial (K, Na)NbO₃ thick films by repeated hydrothermal deposition technique

Abstract

{001}_c-oriented (K_0.86Na_0.14)NbO₃ thick films were prepared at 240°C on (100)_cSrRuO₃//(100)SrTiO₃ substrates by repeated hydrothermal deposition technique. The film thickness was found to increase linearly with the number of deposition cycles, and 60 µm-thick film was obtained after nine repetitions of the deposition. The K/(K+Na) ratio of the deposited thick films, measured by X-ray fluorescence spectroscopy, showed constant values regardless of the number of deposition cycles. Cross-sectional scanning electron microscopy images revealed uniformity of the obtained dense films with no obvious micro cracks and pores. Structural characterization based on X-ray diffraction, XRD 2θ-ω patterns and X-ray pole figure measurement, showed that the epitaxial relationship between the films and substrates with a {001}_c orientation was maintained throughout the deposition cycles. In addition, cross-sectional Raman spectra showed that 60 µm-thick (K_0.86Na_0.14)NbO₃ film had an orthorhombic structure. The dielectric constant, ε_r, and tan δ showed frequency dependence. The average remanent polarization measured at 100 Hz was 8 µC/cm².