Ferroelectric Domain Structure of Na0.5K0.5NbO₃Crystal Grown by Floating Zone Method

The ferroelectric domain structures of orthorhombic Na 0.5 K 0.5 NbO 3 (NKN) crystals grown by the floating zone method are characterized. Three types of laminar domain of 30–80, 10–15, and 5–10 µm in width were found in the crystal cut perpendicular to the growth direction. The thinnest laminar domains were observed between two different 90° domains. Raman spectroscopy confirmed that the NbO 6 units of the NKN perovskite-type structure in the thinnest domains were distorted compared with these in the neighboring laminar 90° domains. When an external electric field was applied vertically to the domain walls, the thinnest domain could release strain caused by the external electric field, and the strain was dispersed in several directions within the thinnest domains. The polarization response per cross section was enhanced by distorted NbO 6 units in the case that the domain structures included the thinnest domains between wide laminar 90° domains.