Domain structures in Pb(Zr, Ti)O 3 and PbTiO 3 thin films
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Domain structures in Pb(Zr, Ti)O3 and PbTiO3 thin films L. D. Madsena) Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4M1
E. M. Griswold and L. Weaver Materials and Metallurgical Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6 (Received 10 December 1995; accepted 16 April 1997)
The microstructure of Pb(Zr, Ti)O3 (PZT) and PbTiO3 (PT) thin films deposited by the sol-gel method and chemical vapor deposition, respectively, were examined by transmission electron microscopy (TEM). Domains with ,7 and ,20 nm widths were found for the PZT and PT thin films, respectively. The traditional parallel twin or wedge-type structures found in bulk ceramics have been observed in thin films. Differences between observed grain sizes and previous studies of similar compounds (in bulk form) are accounted for by geometrical considerations related to crystallographic factors. Finally, a classification scheme for domains in PZT and PT thin films based on these and other published results of several researchers is presented. Domain sizes varied according to three categories: mono-domains (2–50 nm in diameter), domains in spherulite lamellae (28–130 nm wide), and twins in conventional large grains (5–150 nm wide). The mono-domains are related to small grain sizes, while the lamellae are a function of the nucleation and growth associated with sol-gel processing.
I. INTRODUCTION
The fundamental behavior and characteristics of a ferroelectric material can be described in terms of a capacitor. The relationship between the measured resultant polarization and applied electric field is represented by a hysteresis loop. Initially, the net macroscopic polarization can be zero and overall electric dipole direction random. Regions where the dipoles are aligned are called domains. Upon application of a field, the domains will grow and eventually reach maximum alignment when saturation of polarization, Ps , is reached. In general, only easy directions are polarized into domains. The direction of Ps is called the polar axis.1 If the field is removed, some dipoles will remain aligned, giving a remanent polarization, Pr . To reduce the polarization to zero, a coercive field, Ec , must be applied in the opposite direction. The ferroelectric domain structure is formed by twins which accommodate the stress in the material during the cubic to noncubic transformation.2 The basic mechanism by which ferroelectricity takes place is through the formation and motion of domains. Transmission electron microscopy (TEM) imaging can reveal the microstructure of the material, including the domain structure, interfacial characteristics, and a)
All correspondence should be directed to L. D. Madsen, Department of Physics, Link¨oping University, S-581 83 Link¨oping, Sweden; electronic mail [email protected].
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J. Mater. Res., Vol. 12, No. 10, Oct 1997
growth pattern of the film (for example, whether it is epitaxial or columnar). Orientation relationsh
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