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Epitaxial Growth of (Na,K)NbO3 Films by Pulsed Laser Deposition K. Sakurai1,2, T. Hanawa1,2, N. Kikuchi1,2, K. Nishio2, K. Tonooka1, R. Wang1, H. Bando1, and H. Takashima1 1 National Institute of Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba-shi, Ibaraki 305-8568, JAPAN 2 Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, JAPAN ABSTRACT (Na,K)NbO3 is a promising candidate for lead-free piezoelectric materials.     (Na1-xKx)NbO3 films (x = 0.3–0.7) were epitaxially grown on a (100)SrTiO3 substrate via pulsed laser deposition. The effects of substrate temperature and oxygen pressure during deposition on the crystallinity of the films were examined: both parameters affected the mosaic spread of the crystallites and the formation of an impurity phase. In this study, the optimum conditions for the preparation of highly crystalline films were a substrate temperature of 800 °C and oxygen pressure of ~60 Pa. The lattice constants parallel and perpendicular to the substrate surface responded differently to changes in x: the constant parallel to the surface increased with increasing x, while the constant perpendicular to the surface was maximized at x = 0.5. The difference in the dependence of the lattice constants could be explained by the elastic distortion of the lattice. INTRODUCTION Piezoelectric materials are used for various electronic devices such as ultrasonic sensors, gyro sensors, fuel injectors for diesel engines, print-heads for ink-jet printers, and so on. Recently, harvesting of mechanical energy, such as vibration, which can be converted to electrical energy via piezoelectric actuators, has attracted a lot of attention because of energy conservation measures [1,2]. Typical piezoelectric materials are lead-containing perovskites such as Pb(Zr,Ti)O3 (PZT). However, it is likely that the use of these lead-containing materials in electrical devices and vehicles will be restricted in the near future because of their toxicity [3]. Although BaTiO3 is a known lead-free piezoelectric material, its lower Curie temperature (Tc) than that of PZT is a problem for industrial applications. Alkaline niobate-based ceramics, in particular the (Na,K)NbO3 series, are promising candidates for lead-free piezoelectric materials because they have a high Tc and piezoelectricity comparable with those of PZT [4,5]. (Na,K)NbO3-LiTaO3, which has a Tc of ~250 °C, has been reported to have high piezoelectric constants (d33) of ~300 pC/N and 416 pC/N for ceramics without and with texturing, respectively [6]. A (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 system (Tc = 243 °C ) has been reported to exhibit a higher d33 of 420 pC/N without any texturing [7]. In this study, (Na1-xKx)NbO3 (NKN) films were deposited on (100)SrTiO3 (STO) substrates via pulsed laser deposition (PLD) as the first step to the deposition of films with a complex composition of BaZrO3 and (Bi,Li)TiO3 containing (Na,K)NbO3. Several reports on (Na,K)NbO3 films have been published [4,8,9]; however, t