Study on domain structure of NaNbO3 films by laser beam scanning microscope and piezoresponse force microscope

Domain structures of 001-, 110-, and 111-oriented NaNbO₃ (NN) films deposited on SrRuO₃/(001), (110), and (111)SrTiO₃ (STO) substrates, respectively, were characterized by a laser beam scanning microscope (LSM) and a piezoresponse force microscope (PFM). The 001-oriented NN film had antiferroelectric 90° domains with 100 and 010 polarization axes and 90° domain walls exhibiting piezoresponse. The piezoresponded domain walls would be induced by ferroelasticity. On the other hand, the 110- and 111-oriented NN films possessed 60° domains. The 60° domains of 110-oriented NN film were constructed by antiferroelectric 1̅10 domain and piezoresponded {101} and {011} domains. In the case of 111-oriented NN, three kinds of 60° domains (1̅10 and 0̅11, 0̅11 and 10̅1, and 10̅1 and 1̅10) were observed. The fine domains with piezoresponse were also observed in the mixed region with the three 60° domains. From the stress measurement, we found that the difference in the domain structure of 001-, 110-, and 111-oriented NN films depends on not only the orientation direction but also the stress from the substrate.