La7Ru3O18 and La4.87Ru2O12: Geometric Frustration in Two Closely Related Structures with Isolated RuO6 Octahedra
✍ Scribed by P. Khalifah; Q. Huang; D.M. Ho; H.W. Zandbergen; R.J. Cava
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 487 KB
- Volume
- 155
- Category
- Article
- ISSN
- 0022-4596
No coin nor oath required. For personal study only.
✦ Synopsis
The crystal structures of La 7 Ru 3 O 18 and La 4.87 Ru 2 O 12 have been solved from powder neutron di4raction data (R p ؍ 0.032) and single-crystal X-ray di4raction data (R w ؍ 0.070 for all 3125 re6ections), respectively. Although these compounds are both the 5rst example of their structure types, La 7 Ru 3 O 18 , La 4.87 Ru 2 O 12 , and the known compound Sr 5 Re 2 O 12 all have closely related structures. La 7 Ru 3 O 18 crystallizes in the rhombohedral space group R3 c, with cell constants of a ؍ 9.83677(23) A s and c ؍ 56.3493(16) A s in the hexagonal setting, and with Z ؍ 12 formula units per cell. Monoclinic La 4.87 Ru 2 O 12 crystallizes in the P2 1 /c space group with cell constants of a ؍ 5.5798(6) A s , b ؍ 10.1286(11) A s , c ؍ 19.0095(20) A s , ؍ 90.815(4)3, and Z ؍ 4. These structures contain isolated RuO 6 octahedra (d Ru+Ru &5.7 A s ), which are organized into well-de5ned layers having trigonal or pseudo-trigonal symmetry. Furthermore, the three-dimensional patterning of Ru atoms is a nearly perfect close-packed arrangement, despite the large Ru+Ru distances. Magnetic measurements show that geometric frustration suppresses the ordering of the Ru spins and that monoclinic La 4.87 Ru 2 O 12 is more frustrated than rhombohedral La 7 Ru 3 O 18 .