A STRUCTURAL STUDY OF FACET AND OFF-FACET PARTS OF RARE-EARTH GARNETS, GD3SC2AL3O12, GD3SC2GA3O12, AND LA3LU2GA3O12

The crystal structures of facet and off-facet parts of rare-earth garnets Gd3Sc2Al3O12 (GSAG), Gd3Sc2Ga3O12 (GSGG), and La3Lu2Ga3O12 (LLGG) have been refined with the single-crystal X-ray diffraction method. The crystals are cubic with the space group Ia3d, containing eight formula units in a unit cell. The final weighted reliability factors are 0.014, 0.017, and 0.020 for 1786, 2318, and 2331 reflections of the facet parts of GSAG, GSGG, and LLGG, respectively, and 0.014, 0.017, and 0.019 for 2143, 2190, and 2420 reflections of the off-facet parts of the respective crystals. The bond lengths between the tetrahedral cations (T) and the oxygen atoms in GSAG and GSGG as well as those between the dodecahedral cations (Mviii) and oxygen atoms in all the examined crystals are in accordance with the sums of ionic radii both in facet and off-facet parts, whereas the octahedral cations (Mvi) in all the crystals and the tetrahedral cation in LLGG have bond lengths longer than the sums of the ionic radii. A cation replacement at the T sites was not observed, whereas the Mvi and Mviii sites were revealed to be partly replaced by cations with smaller ionic radii. © 1994 Academic Press, Inc.