CRYSTAL GROWTH AND CHEMISTRY OF RARE EARTH ALUMINUM BORATES. D.Y. Choi, S.T. Jung, S.J. Chung, Dept. of Inorganic Materials Engineering, Seoul National Univ., Seoul 151-742, Korea
The crystal structures of rare earth aluminum borates with the general chemical formular of ReAl3(BO3)4 (Re=Y,Gd and Nd) are well known as the isostructure of huntite. Several single crystals of these borates and their solid solutions were grown by top seeded solution growth(TSSG) technique. The space group of grown crystals could be confirmed as R32 for YAl3(BO3)4(YAB) and C2/c for NdAl3(BO3)4(NAB), irrespective of their growth conditions. But the space group of GdAl3(BO3)(GAB) grown above 1030deg.C could be determined as C2 whereas the space group of this crystal grown at about 1000deg.C is R32. The phase diagrams of YAB-NAB and GAB-NAB were determined by x-ray powder diffraction and differential thermal analysis. The structural relations between these borates and the huntite could be explained with their unit cell transformations. The growth forms of YAB and GAB with the space group of R32 are composed of six rhombic and six prismatic planes. The morphological changes of NAB crystal were dependent on the flux compositions. X-ray topography of the grown crystals were carried out and the optical and laser properties of the prepared specimen were examined.