Orientation relationships of unidirectionally aligned GdAlO₃/Al₂O₃ eutectic fibers

Unidirectionally solidified rare-earth activated GdAlO₃(GAP)/Al₂O₃ eutectic crystal with well-aligned fibrous structure exhibits excellent light guiding property and can be used as a scintillator plate for high-resolution X-ray imaging. In this paper, the microstructures and orientation relationships of the GAP/Al₂O₃ eutectic fibers were investigated. The regular GAP single crystal fibers with a hexagonally close-packed arrangement grew straight in the same direction along the solidification direction, and were embedded in a c-axis oriented Al₂O₃ single crystal matrix. The majority of GAP fibers had the orientation relationships of [010]GAP//[0001]Al₂O₃ to the growth direction and (1 0 0)GAP//(1 1 2 0)Al2O3 to the interface plane, while slight misorientation angle of both [010]GAP axis and (100)GAP plane were observed. In the GAP/Al₂O₃ interface boundary, the lattice misfit between the two phases was relieved by insertion of extra half-planes on the Al₂O₃ side.