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Sol-gel Sr 2 Nb 2 O 7 thin films were deposited on Si(100) and Pt-coated Si substrates for the first time by spin-coating. The Sr2Nb2O7 precursor solution was prepared from strontium metal dissolved in 2-methoxyethanol, acetylacetone, and niobium ethoxide. The formation of phase pure Sr2Nb2O7 occurred via an intermediate perovskite phase of composition close to Sr0.82NbO3. Crack-free Sr 2 Nb 2 0 7 films of —0.4 /xm thickness were deposited on these substrates using a single-coating followed by heat treatment at 850 °C for 12 h. SEM microstructure and thin film XRD results indicated the deposition of a grain-oriented film on the Pt-coated Si substrate. The room temperature dielectric constant and the loss values of the film measured at 10 kHz are 45 and 0.045, respectively.

I. INTRODUCTION The observation of ferroelectricity coupled with high Curie temperature has generated much interest in the study of layered perovskites of the general formula A 2 B 2 O 7 . Among these compounds, La 2 Ti 2 0 7 and Sr 2 Nb 2 0 7 exhibit high coercive field and thermal stability.1'2 In addition to being ferroelectric, these materials also show excellent piezoelectric and electrooptic properties for possible use as high temperature transducers.2'3 The crystal structure of Sr 2 Nb 2 0 7 is orthorhombic at room temperature with the space group, Cmc2\. It is built up of slabs of NbO 6 octahedra with strontium along the [010] direction.4 Single crystals of Sr 2 Nb 2 0 7 grown by float-zone technique exhibit two ferroelectric transitions at —156 °C, and also undergo a normal to incommensurate phase transition at 215 CC.5~7 Besides being ferroelectric, they also have piezoelectric and electro-optic properties comparable to those of LiTaO3 and Ba 2 NaNb 5 0i 5 . 5 Attempts to grow Sr 2 Nb 2 O 7 single crystal fibers by the laser-pedestal growth technique have been unsuccessful.8 Samples of polycrystalline ceramics, prepared from SrCO3 and Nb 2 O 5 by conventional powder mixing method, have been found to have a small amount of Sr 5 Nb 4 Oi 5 as an impurity.9 Since single crystals of these materials are impractical for device applications due to excessive cost, fabrication of thin films is highly desirable. Ishitani and Kimura10 reported the deposition of Sr 2 Nb 2 O 7 thin film by rf sputtering onto a b-plate Sr 2 Ta 2 0 7 substrate for possible use as an optical waveguide.

a) Present

address: School of Chemistry, Andhra University, AP 530003, India. b) Present address: Paniculate Materials Center, The Pennsylvania State University, University Park, Pennsylvania 16802. c) Also with the Department of Agronomy. 704

http://journals.cambridge.org

J. Mater. Res., Vol. 10, No. 3, Mar 1995

Downloaded: 16 Mar 2015

The sol-gel method has been widely used to deposit high quality ferroelectric thin films. When compared to vacuum-based techniques such as chemical vapor deposition and sputtering, the sol-gel processing has many advantages.11 We have recently reported the preparation of some layered perovskite ceramics and La 2 Ti 2 0 7 thin films