Determination of domain structure and abundance of epitaxial Pb(Zr, Ti)O 3 thin films grown on MgO(001) by rf magnetron
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Determination of domain structure and abundance of epitaxial Pb(Zr, Ti)O3 thin films grown on MgO(001) by rf magnetron sputtering Kyeong Seok Lee, Young Min Kang, and Sunggi Baik Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea (Received 26 February 1997; accepted 9 September 1998)
Epitaxial Pb(Zrx Ti12x )O3 (x 0.0–0.32) ferroelectric thin films of 500 nm thickness were grown on MgO(001) single crystal substrates by in situ rf magnetron sputtering, and evolution of their domain structures is characterized by employing various x-ray diffraction techniques. X-ray u-2u scan showed the films were grown highly c-axis oriented with a tetragonal perovskite structure. 90± domain configuration was investigated using the x-ray rocking curve analysis for PZT 100 peaks in two different f angles. The rocking curve analysis showed that the degree of c-axis orientation and the crystalline quality of the films were improved continuously with increasing Zr concentration. The c-domain abundance as a function of Zr concentration was quantified using the x-ray rocking curves of PZT 001 and 100, taking account of structural factors and Lorentz-polarization factors. High temperature x-ray technique was also employed to quantify the domain structure as a function of temperature during cooling after reheating the samples to 650 ±C. During the cooling process, c-domain abundance was found to increase continuously while the crystalline quality of the films was deteriorated below the Curie temperature. The results led us to conclude that the transformation strain of the film at and below the Curie temperature plays a significant role in the final domain structure and abundance of epitaxial PZT thin films.
I. INTRODUCTION
Ferroelectric thin films of lead-based perovskite materials such as PbTiO3 , Pb(Zrx Ti12x )O3 (PZT), (Pb12x Lax ) (Zry Ti12y )O3 (PLZT), etc. have received considerable attention for their attractive physical properties including high dielectric, pyroelectric, piezoelectric, and electro-optic properties. Recently, many studies have been devoted to fabrication, characterization, and practical application of such ferroelectric thin films.1–5 Their application to electro-optic waveguide, in particular, requires the deposition of epitaxial films because of their low defect densities and enhanced anisotropic properties displaying high device performance. The epitaxial thin films of ferroelectric oxide materials have been processed mainly by in situ deposition on suitable single crystalline substrates at elevated temperatures of 550 to 650 ±C. The use of dissimilar substrates induces various mechanical and thermal strains in the films due to the mismatches in lattice constants and thermal expansion coefficients between them. In addition, the films being subjected to the cooling process after the in situ deposition undergo structural transformation from a high symmetry phase to a low symmetry phase while c
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