Epitaxial Growth of (Na,K)NbO 3 based materials on SrTiO 3 by pulsed laser deposition
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Epitaxial Growth of (Na,K)NbO3 based materials on SrTiO3 by pulsed laser deposition T. Hanawa1,2, N. Kikuchi1,2, K. Nishio2, K. Tonooka1, R. Wang1, T. Mamiya1 1 National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, JAPAN 2 Graduate School of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika, Tokyo 125-8585, JAPAN
ABSTRACT Lead-free, piezoelectric (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films were epitaxially grown onto (100) SrTiO3 substrate via pulsed laser deposition. The effects of post-annealing temperature on the crystal phases, mosaic spread, and chemical composition of the deposited (Na,K)NbO3 and (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films were analyzed. Results indicate the epitaxial growth of (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films deposited at an oxygen pressure (PO2) of ≥40 Pa and substrate temperature (Ts) of 800°C. The alkaline-deficiency could be suppressed in the (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 films deposited at PO2 ≥ 70 Pa. AFM profile of the (Na,K)NbO3 post-annealed at 1000°C indicates the epitaxial growth of film with atomically flat step-terrace structure, while that of the (Na,K)NbO3-BaZrO3-(Bi,Li)TiO3 film post-annealed at 1200°C shows relatively smooth surface with step-terrace structure and several cubic crystals. It was also found that the preferential evaporation of alkaline components could be suppressed by annealing under covered substrate condition. INTRODUCTION Piezoelectric materials are being widely used in various electronic devices, such as diesel fuel injectors, printer head of ink jet printers, fishing sonars, and so on. Of the different piezoelectric materials, Pb(Zr,Ti)O3 (PZT) and related lead-containing materials are mainly used in the abovementioned applications because of their high piezoelectric constant (for instance d33) as well as high Curie temperature (Tc) [1,2]. Recently, various regulations such as Restriction of Hazardous Substances/End of Life Vehicles (RoHS and ELV) directives have restricted the use of toxic elements, including lead, in electronic devices and vehicles [3]. This has driven the need for the development of new lead-free piezoelectric materials. To this end, several studies have reported various lead-free piezoelectric materials, including BaTiO3, (Bi,Na)TiO3, and (Na,K)NbO3 with a perovskite structure, and Bi4Ti3O12 with a bismuth-layered structure [4-11]. Among them, (Na,K)NbO3 (NKN) and (Na,K)NbO3-based systems have started attracting considerable attention because of their high d33 and Tc. In particular, 0.92(Na0.5K0.5)NbO30.06BaZrO3-0.02(Bi0.5Li0.5)TiO3 exhibits a high Tc of 243°C and d33 of 420 pC/N, comparable to those of conventional PZT, making it a potential lead-free alternative piezoelectric material [12]. In our previous study, we reported the epitaxial growth of NKN films onto (100) SrTiO3 substrates and analyzed the intrinsic properties of the NKN films [13]. However, electrical properties including P-E hysteresis curves and piezoelectric constant could not
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