Synthesis of Sr 2 KNb 5 O 15 Thin Films by Chemical Solution Deposition Method
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Synthesis of Sr2 KNb5 O15 thin films by chemical solution deposition method Wataru Sakamoto, Toshinobu Yogo, Takae Kuroyanagi, and Shin-ichi Hirano Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan (Received 10 February 1997; accepted 9 September 1998)
Crack-free and transparent Sr2 KNb5 O15 (SKN) thin films have been synthesized by the chemical solution deposition method. A homogeneous and stable precursor solution was prepared via controlling the reaction of metal alkoxides. SKN precursor was found to be the complex alkoxide between Sr[Nb(OEt)6 ]2 and KNb(OEt)6 with high structural symmetry. SKN powders and thin films on fused silica substrates directly crystallized to the polycrystalline tetragonal tungsten bronze phase at 600 ±C. Highly oriented SKN thin films with the tetragonal tungsten bronze phase were fabricated on MgO(100) and Pt(100)yMgO(100) substrates. Two crystal lattice planes of SKN were intergrown at an orientation of 18.5± on MgO(100). The dielectric constant of SKN thin films on Pt(100)yMgO(100) was about 590 at 20 ±C at 1 kHz.
I. INTRODUCTION
Strontium potassium niobate (Sr2 KNb5 O15 , SKN) is a ferroelectric material and has a tetragonal tungsten bronze structure, and constitutes filled tungsten bronze.1–4 The electrical properties of SKN are comparable with those of Sr12x Bax Nb2 O6 (SBN) solid solution.5–7 Therefore, SKN has been receiving great attention for application in pyroelectric sensors, surface acoustic wave (SAW) filters, and several electro-optic devices because of its large pyroelectric coefficient, excellent piezoelectric, and electro-optic properties.5–9 SKN ceramics have been prepared by the solid-state reaction of oxide powders at 1300–1350 ±C via the conventional firing and milling techniques.10–12 Kimura et al. prepared SKN ceramics by hot-pressing to improve both the density and the degree of grain orientation.12 SKN single crystals have been grown mainly by the Czochralski method.5–7,13,14 However, the growth of single crystals is usually difficult in terms of the compositional control. Recently, the demand for thin film processing has increased for integrated-device development.15,16 Highly c-axis oriented tungsten bronze SKN thin films are proposed for pyroelectric, piezoelectric, and electrooptic applications. However, synthesis of SKN films has not been reported yet. A chemical solution deposition (CSD) process has been developed for fabrication of ferroelectric films, which provides several advantages, such as high purity, good homogeneity, lower processing temperature, ease of composition control, and versatile shaping.17–24 Hirano and co-workers synthesized highly oriented Sr0.5 Ba0.5 Nb2 O6 (SBN50) and Pb0.6 Ba0.4 Nb2 O6 (PBN60) thin films on MgO(100) and sapphire(C) substrates below 700 ±C using metalorganic compounds.19,23,24 However, the crystallization of ferroJ. Mater. Res., Vol. 14, No. 4, Apr 1999
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