Microstructure and Crystal Chemistry of Eutectic Al2O3/Y3Al5O12 Fibers Modified by the Partial Substitution of Sc2O3 for Al2O3.

Al2O3(corundum)/Y3Al5O12 (garnet, YAG) eutectic fiber samples were produced by the micro-pulling-down (mu-PD) method and the substitution of Sc2O3 for Al2O3 in the Al2O3/Y3Al5O12 eutectic fibers was studied by a scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) together with X-ray diffraction (XRD). The substitution of Sc2O3 UP to 5mol% appears to enhance the formation of the colony texture in the typical "Chinese script structure" with an ordinary crystallographic relationship of [1 (1) over bar0] corundum // [I I I] garnet parallel to the solidification direction and [001] corundum H [(2) over bar 11] garnet perpendicular to the solidification direction. Nevertheless, the further substitution up to 10mol% Sc2O3 induced the primary growth of garnet rods parallel to the solidification direction, and the gap among them was filled by another Chinese script structure with the novel crystallographic relationship of [001] corundum // [100] garnet parallel to the solidification direction. The preference of Sc at the dodecahedral site of the garnet structure, was also confirmed by the single crystal X-ray diffraction.