Relationship between domain structure and film thickness in epitaxial PbTiO 3 films deposited on MgO(001) by reactive sp
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Relationship between domain structure and film thickness in epitaxial PbTiO3 films deposited on MgO(001) by reactive sputtering Won Kyoung Choi, Si Kyoung Choi, and Hyuck Mo Lee Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Kusung-Dong 373-1, Yusung-Gu, Taejon, Korea 305-701 (Received 21 May 1999; accepted 19 September 1999)
The epitaxial PbTiO3 thin films of different thickness were prepared on MgO(001) substrates by the reactive direct-current magnetron sputtering. The volume fraction of c domains, ␣, which was measured by x-ray diffractometry, increased rapidly from zero with the film thickness, being saturated at about 90% above 100 nm. The films were annealed in a PbO atmosphere at 700 °C for 8 h, and they were used to study the composition change in the Pb/(Pb + Ti) ratio and the relaxation of the residual intrinsic stress. The relationship between change of ␣ and composition was weak. The stress state was calculated through the finite-element method. As for the small thickness, the tensile epitaxial stress overwhelmed compressive intrinsic and thermal stresses, and the domain structure was a-domain oriented. As for the large thickness, the compressive intrinsic stress together with the thermal stress overcame the tensile epitaxial stress, and the population turned into c domain.
I. INTRODUCTION
Pb-based ferroelectric ceramics such as PbTiO3, (Pb,La)TiO3, and Pb(Zr,Ti)O3 have received great attention as promising materials for dielectric, pyroelectric, and electro-optic applications.1,2 Recently, because of integration and miniaturization of electronic devices, many studies on ferroelectric thin films with enhanced properties have been reported.3–5 It is widely known that the domain structure of PbTiO3 thin films deposited by the reactive sputtering depends on deposition conditions, substrate types, and deposition methods,6–10 and it is necessary to obtain epitaxial PbTiO3 thin films with only c domains for practical applications.6 Compared with polycrystalline PbTiO3 thin films, epitaxial ones have better properties such as large spontaneous polarization, small dielectric constant, and high pyroelectric coefficient.3– 6,8 The mechanism of domain formation in which the deposition, ferroelectric phase transformation, and cooling is included has been studied,11–16 and the domain structure has been explained in terms of the combined stress, strain, or energy during sample preparation.1,5,7,11–21 When ferroelectric thin films are prepared, the total stress generated is described by the interaction of four types of stress: epitaxial stress ep, intrinsic stress in, thermal stress th, and phase transformation stress tr. Among them, the so-called intrinsic stress is particularly important in sputtering since it is relatively high compared with the other stresses and its magnitude can change with sputtering conditions.15,16,18–21 However, in J. Mater. Res., Vol. 14, No. 12, Dec 1999
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