View Generic Document: Grain Growth and Boundary Migration in Strontium Titanate
Citation:
Lee, Constance (2005). Grain Growth and Boundary Migration in Strontium Titanate. National Institute of Standards and Technology, Technology Administration, U.S. Department of Commerce..
The properties of a polycrystalline material are usually considered to be determined mainly by the composition (phase, phase distribution, etc.) and microstructure (grain size,
porosity, etc.). However most materials are inhomogeneous and anisotropic: not all grains are uniformly sized or randomly oriented throughout the crystal and the material properties vary with
crystal orientation and sample direction. It is important to understand how basic micro-structural changes during grain growth and boundary migration can be influenced to produce desired
microstructures and thus optimum properties. Strontium Titanate, (SrTiO3), was chosen as a model material for a study of grain boundary migration. Single crystal seeds of SrTiO3 of known
orientations were imbedded into polycrystalline material (SrTiO3 + xTiO2) containing random grain orientations. The single crystal seeds were grown into the polycrystalline matrix and can be viewed
as very large grains that provide many interfaces with the polycrystal. Analysis of a large number of interfaces increases the precision of the data. Two sets of samples, each containing 0%, 1%,
and 5% (by volume) excess TiO2, which forms a liquid phase at the sintering temperature, were examined; one sintered at 1500°C for four hours in air and another sintered in a reducing atmosphere of
Ar with 5% H2. Previous observations had shown that the presence of the TiO2-rich liquid phase resulted in greater seed growth and smaller matrix grains as compared with the samples without any
excess TiO2. The presence of a liquid phase combined with the reducing atmosphere resulted in abnormal grain growth (exaggerated growth of a few large grains in the matrix). Orientation mapping of
the interfaces between the single crystal and polycrystal is being conducted on the samples to quantitatively study the effect of grain misorientation on grain boundary migration. Using a scanning
electron microscope (SEM) and electron back-scattered diffraction (EBSD), it is possible to rapidly determine and map the orientation of all the grains on large areas of a sample. Subsets of grains
in the maps have been isolated and pole figures generated and used to determine if there is a misorientation relationship among the grains touching the interface of the single crystal as compared
to the matrix grains. The hypothesis is that specific grain orientations will be absent from the set of interface misorientations to indicate that the single crystal grows more rapidly into grains
of these misorientations.
Publisher
National Institute of Standards and Technology, Technology Administration, U.S. Department of Commerce.
Guest - January 07, 2009
View Generic Document: Grain Growth and Boundary Migration in Strontium Titanate 