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MATERIALS RESEARCH

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Preparation and characterization of SrBi2 Nb2 O9 thin films made by polymeric precursors S. M. Zanetti, E. R. Leite, and E. Longo Departamento de Qu´ımica – UFSCar, P.O. Box 676, 13560-905 S˜ao Carlos, SP, Brazil

J. A. Varela Instituto de Qu´ımica – UNESP, P.O. Box 355, 14801-970 Araraquara, SP, Brazil (Received 24 September 1997; accepted 20 May 1998)

A polymeric precursor solution was employed in preparing SrBi2 Nb2 O9 (SBN) powder and thin films dip coated onto Si(100) substrate. XRD results show that the SBN perovskite phase forms at temperatures as low as 600 ±C through an intermediate fluorite phase. This fluorite phase is observed for samples heat-treated at temperatures of 400 and 500 ±C. After heat treatment at temperatures ranging from 300 to 800 ±C, thin films were shown to be crack free. Grazing incident angle XRD characterization shows the occurrence of the fluorite intermediate phase for films also. The thickness of films, measured by MEV, was in the order of 80–100 nm.

I. INTRODUCTION

Recently, ferroelectric thin films for nonvolatile memory applications have attracted great interest. In particular, those ferroelectric materials belonging to the layered perovskite family, such as SrBi4 Ti4 O15 (SBIT), SrBi2 Ta2 O9 (SBT), and SrBi2 Nb2 O9 (SBN), due to their nonfatigue nature and the possibility of low polarization switching voltage, which were major drawbacks for other materials such as lead zirconate titanate (PZT).1,2 Several deposition techniques have been used to obtain thin films of these compounds, such as pulsed laser ablation,3–5 chemical vapor deposition (CVD),6,7 metallorganic decomposition (MOD),8,9 and sol-gel.10,11 However, these methods require heat treatment at high temperatures, what is seriously deleterious to the Siwafer properties. In this paper, we report the preparation of SBN thin films by the polymeric precursor method, dip coated onto Si(100) and Pt/Ti/SiO2 /Si(100). The polymeric precursor method was proposed by Pechini12 and has been widely utilized to synthesize mixed oxides. The advantage of this method is the possibility of precise stoichiometric control, besides utilization of simple and cheaper reagents as precursors.13,14 As far as we know, no polymeric precursor solutions have been reported for SBN production. II. EXPERIMENTAL

Strontium carbonate, SrCO3 (Merck), niobium ammonium oxalate, NH4 H2 [NbO(C2 O4 )3 ]?3H2 O (CBMM, Arax´a, Brazil), and bismuth oxide, Bi2 O3 (Aldrich) were used as reagents to synthesize SrBi2 Nb2 O9 (SBN). Niobium hydroxide was formed by dissolution of the niobium ammonium oxalate in water and precipitated as 2932

http://journals.cambridge.org

J. Mater. Res., Vol. 13, No. 10, Oct 1998

Downloaded: 16 Mar 2015

Nb(OH)5 by addition of NH4 OH. After filtration, niobium hydroxide was dissolved in an aqueous solution of citric acid to form niobium citrate. The content of Nb was gravimetrically determined as Nb2 O5 . To this niobium citrate solution were added stoichiometric amounts of SrCO3 as salt