Growth of epitaxial Bi_0.5(Na_1-xK_x)_0.5TiO₃ films by hydrothermal reaction time and their characterization

The hydrothermally grown films can be used in various applications because of their relatively lower reaction temperature than the other growth methods. Bi_0.5(Na_1-xK_x)_0.5TiO₃ films on SrTiO₃ substrates are synthesized using the hydrothermal reaction to study its structural and piezoelectric response. The different morphological analysis of films by field emission scanning electron microscope shows the grains on films get through the dissolution-recrystallization process with Ostwald ripening. Also, the structural analyses are carried out using X-ray diffraction and transmission electron microscope which confirmed the formation of epitaxial films with their high crystallinity, and tetragonal symmetry under compressive strain. Through X-ray photoelectron spectroscopy, it was confirmed that the constituent elements and element ratios of BNKT vary according to the reaction time, and the piezoelectric and ferroelectric behaviors were confirmed through a piezoelectric force microscope and piezoelectric coefficient. A combination of the structural and piezoelectric measurements reveals that the reaction time affects the composition of our epitaxial film.