Cubic-to-tetragonal transformation and domain structures in lead titanate (PbTiO(3))
Yang, Li-chang
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https://hdl.handle.net/2142/20552
Description
Title
Cubic-to-tetragonal transformation and domain structures in lead titanate (PbTiO(3))
Author(s)
Yang, Li-chang
Issue Date
1994
Doctoral Committee Chair(s)
Wayman, C. Marvin
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
This thesis focuses on the crystallography of the cubic-to-tetragonal transformation and domain structures in lead titanate from the martensitic transformation point of view.
First, the phenomenological crystallographic theories of the martensitic transformation are considered. Several important aspects of martensitic transformation, such as Bain distortions, lattice correspondences, and habit planes are critically reviewed. Then a direct application of the martensitic theory to the lead titanate case is conducted with particular emphasis on the habit planes and the resulting substructures. It is found from theoretical calculations that there are 24 $\{$023$\}$ habit planes scattered around the six $\{$110$\}$ poles. More importantly, for each habit plane variant there are two crystallographically equivalent substructures.
Later chapters report experimental observations regarding the detailed domain arrangements and the phase transformation as conducted by optical microscopy, scanning electron microscopy, electron back scattering patterns (EBSP) in SEM, and hot stage optical microscopy to parallel the theoretical calculations. The phase transformation in lead titanate is characterized by observing the movement of the habit planes. By measuring the angle between the habit plane and crystal boundary, we deduced possible habit planes to be of the $\{$023$\}$ type. The resulting structures from a single interface transformation were identified with EBSP. It is found that the usual 90 degree domains in lead titanate, in fact, are transformation twins, and the volume fraction of transformation twins measured from scanning electron micrographs is about 3.5/1, which is in good agreement with the theoretical predictions, 3.3/1.
In addition to the single interface transformation, there is a possibility for a transformation proceeding with two or more habit planes. Using a proper temperature-controlled hot stage, a spear-like multiple interface transformation has been observed. In analogy to those in metals, the angle extended by the two habit planes (the spear) are found to be related to their theoretical angular distance in a stereographic projection. The angle of a spear for lead titanate was measured to be 25.0$\sp\circ$, which is close to the angular distance, 23.4$\sp\circ$, in the stereographic projection. The spear-like transformation gives the concept of habit plane variants solid experimental proof.
The domain structures studied in this thesis including parallel bands, herringbones, and square-nets have been proved simply to be habit plane variants. (Abstract shortened by UMI.)
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