Physical Properties of (Na_1–xK_x)NbO₃ Thin Film Grown at Low Temperature Using Two-Dimensional Ca₂Nb₃O₁₀ Nanosheet Seed Layer

A monolayer Ca2Nb3O10 (CNO) nanosheet was deposited on a Pt/Ti/SiO2/Si substrate using the Langmuir–Blodgett method. This monolayer CNO nanosheet with a (001) surface termination was used as a seed layer to reduce the growth temperature of the crystalline (Na1–xKx)NbO3 (NKN) film. The crystalline NKN film was preferentially grown along the [001] direction at 400 °C. The ferroelectric and piezoelectric properties of this NKN film were influenced by the postannealing atmosphere due to the variations in the amounts of oxygen vacancies in the NKN film. The crystalline NKN film annealed at 300 °C under 50 Torr O2 atmosphere showed promising ferroelectric and piezoelectric properties; εr of 303 and tan δ of 2.0% at 100 kHz, Ps of 15.3 μC/cm2, Pr of 11.7 μC/cm2, and Ec of 78 kV/cm, and d33 of 139 pm/V. This NKN film showed the lowest leakage current, which can be explained by the Schottky emission mechanism. The Schottky barrier heights of the Pt/NKN and NKN/CNO/Pt interfaces were calculated to be 0.97 and 0.28 eV, respectively. The results of this work suggest a new method to grow crystalline thin films at low temperatures by using metal-oxide nanosheets as the seed layer.