Growth of Epitaxial KNbO3Thick Films by Hydrothermal Method and Their Characterization

KNbO3 films were grown at 240 °C by the hydrothermal method using KOH and Nb2O5 as source materials. Film thickness increased with reaction time up to 3 h, however decreased for longer reaction times. A 16-µm-thick epitaxially grown KNbO3 film with {100}pc orientation were successfully grown on (100)cSrRuO3∥SrTiO3 substrate for 3 h. The relative dielectric constant and dielectric loss at 100 kHz were 415 and 8%, respectively. Clear hysteresis loops originating from ferroelectricity were observed and the remanent polarization was 20 µC/cm2 at the maximum applied electric field of 220 kV/cm. The effective longitudinal piezoelectric constant, d33eff, obtained using a laser Doppler velocimeter, was 86 pm/V.