Acta Cryst. (1999). B55, 266-272 [doi:10.1107/S0108768198012567]
x 5) garnet solid solutionsAbstract: Five single crystals of Y3Al5-xGaxO12 (0 x 5) garnet solid solutions with the compositions x = 0.0, 1.0, 2.0, 3.0 and 4.0 were synthesized using a flux method. The compositional dependence of the lattice constants of the garnet solid solutions shows a large deviation from Vegard's law. Investigation of the cation distributions of these garnets using single-crystal X-ray diffraction shows that Ga3+, which is larger than Al3+, preferentially occupies the tetrahedral (four-coordinate) site rather than the octahedral (six-coordinate) site. On the basis of the results obtained from structure refinements, geometric analyses of the polyhedral distortions were carried out. The results imply that the cation-cation repulsive force across the polyhedral shared edges decreases with increasing substitution of Ga3+. Moreover, the proportion of covalent bonding in the cation-oxygen bonds was estimated from the bond strength; the results indicate that the covalency of the Ga-O bond is greater than that of the Al-O bond. The peculiar cation distributions observed in the Y3Al5-xGaxO12 garnet solid solutions are most probably caused by the strong covalency of the Ga-O bond and also simultaneously induced by the need to decrease the cation-cation repulsive force. Crystal data: cubic, Ia3d, Z = 8, Mo K![[alpha]](/logos/entities/alpha_rmgif.gif)
, ![[bold lambda]](/logos/entities/lambda_bdgif.gif)
= 0.71069 Å; at x = 0.0 (triyttrium pentaaluminium dodecaoxide): a0 = 12.0062 (5) Å, V = 1730.7 (2) Å3, Dx = 4.56 Mg m-3, Mr = 593.613, ![[bold mu]](/logos/entities/mu_bdgif.gif)
= 21.21 mm-1, F(000) = 2224, R = 0.029 for 294 reflections; at x = 1.0 (triyttrium tetraaluminium gallium dodecaoxide): a0 = 12.0432 (7) Å, V = 1746.7 (3) Å3, Dx = 4.84 Mg m-3, Mr = 636.351, = 24.09 mm-1, F(000) = 2368, R = 0.022 for 124 reflections; at x = 2.0 (triyttrium trialuminium digallium dodecaoxide): a0 = 12.0926 (9) Å, V = 1768.3 (4) Å3, Dx = 5.10 Mg m-3, Mr = 679.089, = 26.85 mm-1, F(000) = 2512, R = 0.018 for 144 reflections; at x = 3.0 (triyttrium dialuminium trigallium dodecaoxide): a0 = 12.1552 (6) Å, V = 1795.9 (3) Å3, Dx = 5.34 Mg m-3, Mr = 721.827, = 29.43 mm-1, F(000) = 2656, R = 0.018 for 184 reflections; at x = 4.0 (triyttrium aluminium tetragallium dodecaoxide): a0 = 12.2123 (8) Å, V = 1821.3 (4) Å3, Dx = 5.58 Mg m-3, Mr = 764.565, = 31.97 mm-1, F(000) = 2800, R = 0.014 for 159 reflections.
Online 1 June 1999
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| Structure factor file (SHELXL table format) (8.3 kbytes) |
| Structure factor file (SHELXL table format) (9.7 kbytes) |
| Structure factor file (SHELXL table format) (12.3 kbytes) |
| Structure factor file (SHELXL table format) (10.7 kbytes) |
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