4 - Fabrication of (K, Na)NbO3 films by pulsed laser deposition and their domain observation

Abstract

Using pulsed laser deposition, 1–3-μm-thick (KxNa1−x)NbO3 films were epitaxially grown on SrRuO3/(001)SrTiO3 substrates. It was confirmed that the crystal systems of the films were orthorhombic at x=0 and 0.005, monoclinic at x=0.11–0.34, and orthorhombic at x=0.47–0.60. Ferroelectric polarization–electric field loops were observed at x=0–0.87. Remanent polarization was maximized to ~40μC/cm2 at x=0.34. To understand the change in the remanent polarization with x, domain structures of the films with x=0–0.30 were observed by confocal laser scanning microscopy. It was found that the films consisted of stripe domains with in-plane polarization directions at x=0, mixtures of line and stripe domains with in-plane and out-of-plane polarization directions at x=0.005 and 0.11, and stripe domains with out-of-plane polarization directions at x=0.18 and 0.30. After an electric field was applied for the films in the out-of-plane direction, some domains with in-plane polarization directions were changed to domains with out-of-plane polarization directions at x=0–0.11. These observations suggested that the change of the remanent polarization with x was attributed to the change in the domain structures.