GSAG and YSAG: a study on isomorphism and crystal growth

The composition of gadolinium-scandium-aluminium (GSAG) and yttrium-scandium-aluminium (YSAG) garnet crystals grown by the Czochralski method and by floating zone melting was analysed. It is shown that Sc³⁺ and Al³⁺ ions in GSAG and Y³⁺, Sc³⁺ and Al³⁺ ions in YSAG can simultaneously occupy two types of sites in the lattice. The congruent melting composition of GSAG is {Gd_2.88Sc_0.12} [Sc_1.77Al_0.23] (Al₃)O₁₂. The homogeneity range of GSAG is rather narrow. In the Y₂O₃-Sc₂O₃-Al₂O₃ system a wide range of garnet-structured solid solutions exist. However, there is no ternary garnet that melts congruently. Distribution coefficients of components in YSAG are slightly varied from unity in the whole concentration range, and as the melt composition approaches YAG they tend to unity. Cr³⁺ and Nd³⁺ distribution coefficients in GSAG and YSAG are presented.