La7Ru3O18 and La4.87Ru2O12: Geometric Frustration in Two Closely Related Structures with Isolated RuO6 Octahedra
La7Ru3O18 and La4.87Ru2O12: Geometric Frustration in Two Closely Related Structures with Isolated RuO6 Octahedra
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La7Ru3O18 和 La4.87Ru2O12：两个密切相关的孤立 RuO6 八面体结构中的几何挫败
DOI：
10.1006/jssc.2000.8933
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
R. Cava
中科院分区：
文献类型：
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作者：
P. Khalifah;Q. Huang;Q. Huang;D. Ho;H. Zandbergen;R. Cava
摘要利用粉末中子衍射数据（Rp=0.032）和单晶x射线衍射数据（Rw=0.070）分别求解了La7Ru3O18和La4.87Ru2O12的晶体结构。虽然这些化合物都是其结构类型的第一个例子，但La7Ru3O18， La4.87Ru2O12和已知的化合物Sr5Re2O12都具有密切相关的结构。La7Ru3O18在r3c菱形空间群中结晶，六边形晶胞常数为a=9.83677(23) a和c=56.3493(16) a，每个晶胞的公式单位为Z=12。单斜晶型La4.87Ru2O12在P21/c空间群中结晶，晶胞常数为a=5.5798(6) a, b=10.1286(11) a, c=19.0095(20) a, β=90.815(4)°，Z=4。这些结构包含孤立的RuO6八面体（dRu-Ru ~ 5.7 A），它们被组织成具有三角形或拟三角形对称的明确层。此外，尽管Ru - Ru之间的距离很大，但Ru原子的三维图案几乎是完美的紧密排列。磁测量表明，几何挫折抑制了Ru自旋的有序，单斜体La4.87Ru2O12比菱形体La7Ru3O18更受挫折。
Abstract The crystal structures of La7Ru3O18 and La4.87Ru2O12 have been solved from powder neutron diffraction data (Rp=0.032) and single-crystal X-ray diffraction data (Rw=0.070 for all 3125 reflections), respectively. Although these compounds are both the first example of their structure types, La7Ru3O18, La4.87Ru2O12, and the known compound Sr5Re2O12 all have closely related structures. La7Ru3O18 crystallizes in the rhombohedral space group R 3 c, with cell constants of a=9.83677(23) A and c=56.3493(16) A in the hexagonal setting, and with Z=12 formula units per cell. Monoclinic La4.87Ru2O12 crystallizes in the P21/c space group with cell constants of a=5.5798(6) A, b=10.1286(11) A, c=19.0095(20) A, β=90.815(4)°, and Z=4. These structures contain isolated RuO6 octahedra (dRu–Ru∼5.7 A), which are organized into well-defined 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 La4.87Ru2O12 is more frustrated than rhombohedral La7Ru3O18.