Hydrothermal epitaxy of KTaO3 thin films under supercritical water conditions

Potassium tantalate powders were hydrothermally synthesized at 400 °C using Ta 2 O 5 and KOH as starting materials with various KOH concentrations (0.1–1.0 M) and heating durations (2–48 h). A defect pyrochlore phase of KTa 2 O 5 (OH)· n H 2 O, was obtained at low KOH concentration and short reaction time. The perovskite phase of KTaO 3 predominated as the heating duration and the KOH concentration increased. Pure KTaO 3 was obtained in 0.5–1.0 M KOH aqueous solutions and reaction times of 8–48 h. Heteroepitaxitial KTaO 3 thin films were achieved on the (100) SrTiO 3 substrate in 0.5 M KOH solution under supercritical water conditions. Based on the XRD, SEM-EDX and EBSP (Electron BackScatter Pattern) results, epitaxial KTaO 3 crystals were grown on the (100) oriented single-crystal SrTiO 3 substrate. Synthesis of perovskite KTaO 3 crystals in supercritical water employed significantly low KOH concentrations (7 M) required for conventional hydrothermal method.