Abstract: Lu_xY_1-xAlO₃:Ce single crystal samples were prepared by the Czochralski method. Based on X-ray diffraction (XRD) and composition analyses, and analysis of phase diagram of Lu₂O ₃-Al₂O₃ and the structural stability of Lu_xY_1-xAlO₃:Ce, it is supposed that as the content of Lu increase, the melt delamination is exacerbated, and the crystallization interval of Lu_{x 1-x}AlO₃:Ce in the phase diagram may shift towards the interval rich in Lu, resulting in the accompaniment of (Lu,Y)₃Al₅O₁₂:Ce on the top of Lu_xY_1-xAlO₃ :Ce single crystals. With the increase of the content of Lu, the thermal stability of Lu_xY_1-xAlO₃:Ce single crystals decreases, the oxygen vacancy in those crystals furthers the decrease, so the seed surface tends to decompose into (Lu,Y₃ Al₅O₁₂:Ce and (Lu,Y)₄Al₂O₉:Ce while seeding, and the former decomposition product provides the crystal nucleus to induce crystallization of (Lu,Y₃Al ₅O₁₂:Ce, resulting in the accompaniment of (Lu,Y)₃Al₅O₁₂:Ce on the coat of Lu_xY_1-xAlO₃:Ce single crystals. An adjustment of the melt composition to make the mol ratio n((Lu,Y)₂O₃):n(Al₂O₃) equal to 1.17--1.00, and a greater temperature gradient inside the melt and at the solid liquid interface to improve melt convection, restrain melt delamination and the decomposition on the seed surface may contribute to the acquisition of Lu_x Y_1-xAlO₃:Ce with high Lu content.

Key words: lutetium yttrium aluminate crystals, perovskite, garnet, accompany