Preparation of Barium Titanate Films Using Sol-Gel Techniques
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Preparation of Barium Titanate Films Using Sol-Gel Techniques
R. G. Dosch, Sandia National Laboratories, New Mexico 87185
P.
O.
Box 5800,
Albuquerque,
ABSTRACT Sol-gel techniques provide a convenient method of applying barium titanate films on solid substrates at ambient temperature. A significant advantage in using this technique is the capability of maintaining compositional homogeneity while coating large areas of surfaces with complex geometries. Solutions prepared by reacting a titanium alkoxide with barium hydroxide in methanol were used for preparing thin films (1000-3000A) of barium titanate on silicon and metal substrates. Electrical properties of the films depended both on solution parameters and subsequent heat treatment of the 6 films. Highest field strengths (8-9 x 10 V/cm) were observed in amorphous films prepared from partially hydrolyzed solutions.
Introduction A variety of techniques have been used to prepare barium titanate 4 films(l- ), but most involve either relatively sophisticated apparatus or area and geometrical constraints. Hydrolysis of mixtures of barium 5 napthenate and titanium alkoxides has been successfully used( ) for this purpose, but requires relatively high temperatures to remove organics. In this work, solutions of titanium isopropoxide and barium hydroxide were used to form barium titanate films on Si, Ni, and Ti substrates. This chemical system appears to provide a simple means for coating large areas while maintaining stoichiometric homogeneity. This system also minimizes the organic content of films dried at ambient temperature and provides the option of subsequent alteration of film composition via ion exchange reactions. In this paper, the preparation and associated chemistry of precursor solutions and films are presented. Solution parameters and subsequent thermal history which affect the electrical properties of the films are also discussed.
Experimental Titanium isopropoxide (TPT) was purified by vacuum distillation. Sodium methoxide was added to prevent C1- carryover into the distillate. Ba(OH) 2 was prepared by adding stoichiometric amounts of H20 to a BaO slurry in MEOH. The BaO was prepared by precipitating recrystallized Ba(N03) 2 as barium oxalate which was then heated to form BaCO 3 . The BaCO 3 was converted to BaO at high temperature in glassy carbon crucibles.
*This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract number DE-ACO4-76DP00789. Mat.
Res. Soc. Symp. Proc. Vol.
32 (1984) Published by Elsevier Science Publishing Co,_ Inc.
158
Alcohol solutions containing Ba:Ti mole ratios
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