Grain boundaries in titania-doped alpha-alumina with anisotropic microstructure

The microstructure of sol-gel-derived alpha-alumina (Al2O3) doped with 0.6 wt% titania, sintered at 1450 degrees C for 1 h, consisted of thin platelets with (0001) faces in a matrix of equiaxed grains, Short facets at the edges of the platelets developed primarily parallel to the {10 (1) over bar 2} planes, while some were parallel to the {11 (2) over bar 3} planes; other edges showed irregular, curved boundaries, The basal surfaces of the platelets were coated with thin layers (0.5-6 nm) of an amorphous titanium-containing aluminosilicate phase, which also was present at triple points, No amorphous phase was found on the short faceted boundaries, on curved boundaries at platelet edges, or at grain boundaries of equiaxed, matrix grains. However, titanium enrichment was observed at all examined boundaries, suggesting that titanium segregation alone did not account for the development of anisotropic microstructure. Curved incursions on basal facets were associated with occasional particles of aluminum titanate (Al2TiO5).