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(a) Plane-view SEM image of nanosized island on Nb doped- fabricated by hydrothermal epitaxy at 160 °C, for 30 min; and (b) x-ray diffraction pattern of thin film. The inset represents (101) pole figure of thin film. Note that x-ray diffraction analysis was carried out on a sample with denser islands, which was grown for a prolonged fabrication time of 16 h.
(Color) (a) Piezoresponse image of a island with positive polarization. The inset shows a piezoresponse image after polarization switching by −10 V poling on the white arrowed region; (b) piezoresponse image of islands with positive polarization (A), and negative polarization (B and C). The inset shows a piezoresponse image after polarization switching by +10 V poling on a part of C island.
Size dependence of initial polarization direction of island determined by PFM analysis. There is a critical size that determines the direction of the polarization at the as-fabricated state. The size of island was determined by AFM.
Schematics diagrams of representing (a) the epitaxial growth of a tetragonal island with positive polarization in a hydrothermal solution; (b) the energy barriers in potential well according to ferroelectrics size; and (c) the spontaneous polarization reversal for compensating the depolarization field below a critical size in Fig. 3. Note that, above a critical size, the island maintains its initial positive polarization because of the high energy barrier for domain switching.
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