Laser scanning microscopy observation of domain switching in NaNbO3 epitaxial film

Domain patterns of a 001-oriented NaNbO₃ film prepared on a SrRuO₃/(001)SrTiO₃ (STO) substrate were observed by laser scanning microscopy during the application of the ac electric field amplitude of 100 kV/cm. The domain patterns consisted of vertical and horizontal stripes along the [100] and [010] directions of the (001) STO substrate and slanted stripes along the [110] and [1-10] directions. Only the slanted domain patterns changed with the electric field. When the electric field decreased from +100 kV/cm to -100 kV/cm, some slanted domain patterns shrank in the stripe direction and completely disappeared near the coercive field, and then reappeared and expanded in the stripe direction upon further decrease of the electric field while other domain patterns just shrank and expanded in the stripe direction without disappearance. These results suggested two kinds of domain switching route in the 001-oriented NaNbO₃ thin film.