Synthesis and structure of preferred-oriented Li₂O-Nb₂O₅-TiO₂ thin film with superstructure

Li_1.18Nb_0.82Ti_0.18O₃ thin film, which has LiNbO₃-based subcell and resultant superstructure along its c-axis, was prepared on Al₂O₃ (0001) single-crystal substrate from alkoxide solutions by a sol-gel and a spin-coating process. The high-temperature X-ray diffraction measurement indicated that the coated gel film was crystallized at 500 °C, and the superstructure was formed at 800 °C. Thickness of the prepared film was typically 100 nm, and was synthesized by a one-step coating process. In order to achieve coexistence of preferred orientation with superstructure in a thin film, a two-step heat treatment was found to be an appropriate method. The layer of the superstructure was parallel to Al₂O₃ (0001) substrate. Some distribution of layer distance was observed by XRD and TEM. However, the degree of preferred orientation for two-step heat-treated film was estimated to be 1.0 by XRD, showing the advantage of the present processing to fabricate preferred-oriented superstructure thin film.