Epitaxial growth of PbZr 0.5 Ti 0.5 O 3 thin films on (001) LaAlO 3 by the chemical solution deposition method
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Epitaxial growth of PbZr0.5Ti0.5O3 thin films on (001) LaAlO3 by the chemical solution deposition method J.H. Kima) Department of Ceramic Engineering, Chonnam National University, 300 Yongbong-Dong, Puk-Ku, Kwangju, 500-757, South Korea
F.F. Lange Materials Department, College of Engineering, University of California, Santa Barbara, California 93106 (Received 13 August 1998; accepted 12 July 1999)
Epitaxial PbZr0.5Ti0.5O3 (PZT) thin films were grown on (001) LaAlO3 substrates (∼6.1% lattice mismatch) by the chemical solution deposition method. The sequence of epitaxy during heating between 375 and 700 °C/1h was characterized by x-ray diffraction and transmission electron microscopy. At approximately 375 °C/1h, a nanocrystalline metastable fluorite phase of PZT was formed from the pyrolyzed amorphous precursor. At higher temperatures (400–425 °C/1h), thermodynamically stable PZT crystallites were first observed at the interface; with increasing higher temperatures, these nuclei grew across the interface and through the film toward the surface by consuming the metastable nanocrystalline fluorite grains. PZT thin films annealed above ∼500 °C/1h were observed to be dense with an epitaxial orientation relationship of [100](001)PZT㛳[100](001)LAO. The metastable nanocrystalline fluorite to the stable single-crystal perovskite transformation gives an extra driving force by providing an additional decrease in free energy in addition to a driving force from the elimination of grain boundary area for epitaxy.
I. INTRODUCTION
Ferroelectric thin films have numerous potential device applications by utilizing the unique dielectric, pyroelectric, acoustooptic, electrooptic, and piezoelectric properties. It has been known that conventional polycrystalline ferroelectric thin films grown on Pt–Ti base electrodes suffer from the presence of high-angle grain boundaries detrimental to device performance. Therefore, preparation of high-quality epitaxial single crystal ferroelectric thin films has been studied over the past few years because they can take full advantage of the anisotropic properties for optical and electronic applications.1,2 A variety of different techniques have been developed to grow oriented or epitaxial ferroelectric thin films such as Pb(ZrxTi1−x)O3 (PZT) on single crystal substrates [e.g., sputtering,3 laser ablation,4 metalorganic chemical vapor deposition,5 and chemical solution deposition (CSD)6]. Among them, the CSD is of particular interest because of its good control of stoichiometry, ease of fabrication, and low temperature synthesis. The CSD method is relatively new and requires a greater understanding to optimize film quality. Crystala)
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J. Mater. Res., Vol. 14, No. 10, Oct 1999 Downloaded: 22 Mar 2015
lization mechanisms in CSD-derived thin films are different from phenomena associated with vapor phase epitaxy.7 It was reported that CSD derived thermodynamically stable, perovskite PbTiO3
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