Growth and Characterization of Na 0.5 K 0.5 NbO 3 Thin Films on Polycrystalline Pt 80 Ir 20 Substrates
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Staffan Rudner Department of Physics, Linko¨ping University, SE-581 83 Linko¨ping, Sweden, and Swedish Defence Research Agency (FOI), Box 1165, SE-581 11 Linko¨ping, Sweden
Ivan P. Ivanovd) Department of Physics, Linko¨ping University, SE-581 83 Linko¨ping, Sweden
Alex Grishin Department of Condensed Matter Physics, Royal Institute of Technology, Electrum 229, SE-164 40 Stockholm-Kista, Sweden
Ulf Helmersson Department of Physics, Linko¨ping University, SE-581 83 Linko¨ping, Sweden (Received 5 February 2002; accepted 28 February 2002)
Na0.5K0.5NbO3 thin films have been deposited onto textured polycrystalline Pt80Ir20 substrates using radio frequency magnetron sputtering. Films were grown in off- and on-axis positions relative to the target at growth temperatures of 500–700 °C and sputtering pressures of 1–7 Pa. The deposited films were found to be textured, displaying a mixture of two orientations (001) and (101). Films grown on-axis showed a prefered (001) orientation, while the off-axis films had a (101) orientation. Scanning electron microscopy showed that the morphology of the films was dependent on the substrate position and sputtering pressure. The low-frequency (10 kHz) dielectric constants of the films were found to be in the range of approximately 490–590. Hydrostatic piezoelectric measurements showed that the films were piezoelectric in the as-deposited form with a constant up to 14.5 pC/N.
I. INTRODUCTION
The perovskite compound KNbO3 is a ferroelectric material1 with important applications in electro-optical modulation, nonlinear laser light interaction, and optical storage.2 NaNbO3, also a perovskite, is, on the other hand, an antiferroelectric material.3 The continuous solid solution of these two compounds, NaxK1−xNbO3, is a ferroelectric perovskite when x < 0.97 and has mainly been studied in ceramic form in the 1950’s and 1960’s.4–7 NaxK1−xNbO3 has a relatively high piezoelectric constant and a Curie point at around 300–400 °C, which a)
Present address: Acreo AB, Bredgatan 34, SE-602 21 Norrko¨ping, Sweden. b) Present address: University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland. c) Present address: Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. d) Present address: Cypress Semiconductor Inc., 2401 East 86 Street, Bloomington, MN 55425. J. Mater. Res., Vol. 17, No. 5, May 2002
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makes it suitable for many applications. The highest piezoelectric constant reported for this material is d33 ⳱ 160 pC N−1 for a hot-pressed bulk sample with the composition of Na0.5K0.5NbO3.5 To a large degree, knowledge on fabrication and performance of NaxK1−xNbO3 in thin-film form is lacking, although results have been published on fabrication of KNbO3 thin films for nonlinear optical applications.8–14 Only a few studies exist on NaxK1−xNbO3 thin films. Margolin et al.15 have used radio frequency (rf) cathode sputtering of a NaxK1−xNbO3 powder target to grow films on stainless steel substrates where the compos
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