Novel epitaxial growth of barium titanate thin films by electrodeposition
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Novel epitaxial growth of barium titanate thin films by electrodeposition Jun Tamaki,a) Gregory K.L. Goh, and Fred F. Lange Materials Department, University of California Santa Barbara, Santa Barbara, California 93106 (Received 13 March 2000; accepted 29 August 2000)
Electrodeposition was used to grow epitaxially BaTiO3 thin films on SrTiO3 single-crystal substrates with La0.7Sr0.3MnO3 (LSMO) conducting buffer layers. The epitaxial films appeared to consist of very small (艋10 nm) particles. The film completely covered the substrate when the reaction was performed at temperatures between 60 and 90 °C with LSMO potentials of −0.5 to −1.0 V against a Pt counter-electrode. It appeared that an electrophoretic force, acting on BaTiO3 nuclei within the solution, facilitated the deposition of the film. It is well known that barium titanate (BaTiO3) has high dielectric constant and ferroelectric properties, and is an important material in the electronics industry. There is current interest in synthesizing epitaxial films from direct solution routes at relatively low temperatures. Recently, our group has found that BaTiO3 thin films could be epitaxially grown on SrTiO3 single-crystal substrates under hydrothermal conditions at a temperature as low as 90 °C.1–3 A number of investigators have studied the low-temperature, electrochemical–hydrothermal synthesis of polycrystalline ATiO3 (A ⳱ Ca, Sr, or Ba) films on titanium substrates.4–12 In these cases, the titanium (or TiAl) metal electrode contributes the Ti within the ATiO3 thin film by the anodic oxidation of Ti with the A2+ and OH− ions. Because these films grow outward from the interface between the Ti electrode and the ATiO3 film by the transport of both A-site and oxygen atoms from the solution, the initial growth is controlled by charge transfer, which is superseded by mass transfer through the porous film.13,14 Here we report our initial results for producing epitaxial BaTiO3 (BTO) thin film using a hydrothermalelectrodeposition method where the solution contained the same precursors, Ba(OH)2 and TiO2, used in the previous hydrothermal epitaxy1,2 on SrTiO3 single-crystal substrates. For the current study, SrTiO3 (STO) single-crystal substrates (5 × 5 × 0.5 mm; MTI Corp., Richmond, CA) were prepared with a conducting and epitaxial layer of La0.7Sr0.3MnO3 (LSMO) by spin coating an aqueous acetate precursor solution, pyrolyzing the precursor
a)
On leave from the Department of Chemistry, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu-shi, Shiga 525-8577, Japan. J. Mater. Res., Vol. 15, No. 12, Dec 2000
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film (approximately 350 °C for 2 min on a hot plate), and heating to 1100 °C/1h under flowing O2. Based on a method originally developed for producing La0.7Ca0.3MnO3 films,15 the LSMO precursor solution was prepared by dissolving appropriate amounts of La(OH)3, SrCO3, and MnO in a solution of water and acetic acid (1:3 by volume) to contain an equivalent 0.2 molar concentration of LSMO. Bulk ST
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