Laser beam scanning microscope and piezoresponse force microscope studies on domain structured in 001-, 110-, and 111-oriented NaNbO3 films

NaNbO3 (NN) films were epitaxially grown on SrRuO3/(001), (110), and (111)SrTiO3 substrates, and these NN films were characterized by a laser beam scanning microscope and a piezoresponse force microscope. The 001-oriented NN film had antiferroelectric 90° domains with 100 and 010 polarization axes and 90° domain walls exhibiting piezoresponse. The piezoresponding 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 11¯0 domain and piezoresponding {101} and {011} domains. In the case of 111-oriented NN, three kinds of 60° domains (11¯0 and 01¯1, 01¯1 and 101¯, and 101¯ and 11¯0) 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 not only on the orientation direction but also on the stress from the substrate. Moreover, the stress and the induction of the piezoelectric domain also influence the dielectric behavior.