Synchrotron X-ray study of Er3Al5O12 and Yb3Al5O12 garnets.

Structure factors for Er(3)Al(5)O(12) and Yb(3)Al(5)O(12) garnets were measured using focused synchrotron X-radiation, with lambda = 0.7500 (2) and 0.7000 (2) A, respectively. The difference electron density maps for Er(3)Al(5)O(12) and Yb(3)Al(5)O(12) were similar, as expected. This was attributed to the 4f electrons being shielded, which reduces their effectiveness in chemical bonding and the relative position of the rare-earth atoms in the periodic table. The symmetry of the difference electron density around the rare-earth atoms was found to reflect that of the cation geometry, emphasizing the importance of second nearest-neighbor interactions. This is consistent with the view that oxide-type structures may be regarded as a packed array of cations with anions in the interstices.