Titania precipitation in sapphire containing iron and titanium |
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Authors: | Anthony R Moon Matthew R Phillips |
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Institution: | 1. Department of Applied Physics, University of Technology, Sydney, PO Box 123, 2007, Sydney, Australia
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Abstract: | Titania, TiO2, precipitation in natural blue sapphire (Fe, Ti: -Al2O3) has been investigated using high resolution and analytical transmission electron microscopy. The structure and habit of the TiO2 precipitate depends on both the Ti4+ concentration and the temperature at which the precipitate formed. Tetragonal TiO2 (Rutile) grows at 1350° C but at 1150° C an orthorhombic non-equilibrium TiO2 polymorph precipitates. Both TiO2 polymorphs nucleate in the (0001)s plane as lens shaped discs twinned along their diameter. The crystallographic alignment of each type of TiO2 precipitate with respect to the -Al2O3 host matrix provides a high degree of structural coherency with minimal lattice mismatch. Electron diffraction analysis established the following precipitate/host orientation relationships: tetragonal TiO2: {011}r {11
07B;100}r(0001)s and 01
r10
0s twinned along the (011)r planeand orthorhombic TiO2: {021}{11
0}s, {100}(0001)s and 0
2 10
0s twinned along the (021) plane. |
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Keywords: | |
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