Fourier transform infrared analysis of hydroxyl content of hydrothermally processed heteroepitaxial barium titanate film
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Nipun Shah Materials Research Center, University of Missouri-Rolla, Rolla, Missouri 65409
Frank D. Blum Materials Research Center and Department of Chemistry, University of Missouri-Rolla, Rolla, Missouri 65409
Mohamed N. Rahamana) Department of Materials Science and Engineering, University of Missouri-Rolla, Rolla, Missouri 65409 (Received 15 November 2004; accepted 26 July 2005)
The concentration of hydroxyl (–OH) groups in epitaxial barium titanate (BaTiO3) films (thickness ∼ 200 nm), deposited on single-crystal strontium titanate (SrTiO3) at 150 °C by a hydrothermal technique, was investigated using x-ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. After hydrothermal treatment, a broad FTIR resonance for the hydroxyl groups indicated a significant concentration of surface –OH groups in the films. The as-deposited films were subsequently treated hydrothermally with D2O, and the kinetics of the exchange reaction between –OH incorporated into the film and –OD from the D2O were studied using FTIR. For reactions carried out intermittently, the kinetics of the exchange reaction between –OH by –OD depended not only on the total reaction time, but also on the duration of each treatment. The broad FTIR hydroxyl resonance in the as-deposited hydrothermal film was significantly reduced only after heating for 1 h at 600–800 °C.
I. INTRODUCTION
Barium titanate (BaTiO3) thin films are of significant interest for several applications in the electronics industry because of their high-dielectric constant and ferroelectric properties.1 Conventional routes to the synthesis of BaTiO3 films, such as sol-gel processing and vapor phase methods (e.g., metalorganic chemical vapor deposition, sputtering, and pulsed laser deposition), often require high temperatures or high vacuum. There is interest in solution-based methods, such as hydrothermal and electrochemical techniques, because these techniques can provide direct routes to the synthesis of crystalline BaTiO3 films at low temperatures.2–19 The hydrothermal route employs reactions in aqueous solutions at temperatures close to, or above, the boiling point of water to
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0406 3312
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 12, Dec 2005 Downloaded: 19 Nov 2014
deposit crystalline inorganic materials in the form of particles, thin films, or crystals.20 Hydrothermal deposition of heteroepitaxial BaTiO3 films on structurally similar single-crystal substrates, such as SrTiO 3 and LaAlO 3 , has been demonstrated.6,10,13,19 Structural investigations of crystalline BaTiO3 powders, precipitated under hydrothermal conditions similar to those used for the preparation of heteroepitaxial BaTiO3 films, indicate that defects and impurities such as Ba and Ti vacancies, H2O, –OH, and carbonate ions may be incorporated into the crystal lattice during synthesis.21–24 The concentration of these incorporated species depends on synthesis conditions such as t
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