Single-crystal X-ray diffraction study of CaIrO3
Single-crystal X-ray diffraction study of CaIrO3
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DOI：
10.2138/am.2008.2701
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发表时间：
2008-07-01
影响因子：
3.1
通讯作者：
Ohtaka, Osamu
中科院分区：
文献类型：
--
作者：
Sugahara, Masahiko;Yoshiasa, Akira;Ohtaka, Osamu
采用助熔剂法生长了CaIrO 3单晶。晶体结构参数，包括各向异性位移参数，确定基于单晶X射线衍射实验。晶胞尺寸为a = 3.147（2），B = 9.866（6），c = 7.302（5）埃。该结构是一个三维密集结构，具有小的空置空间。CaIrO 3结构可以被描述为准一维氧化物，并与Ca 4 IrO 6结构进行了比较。IrO 6八面体显着扭曲，与其他八面体Ir 4+化合物。多面体之间共享的面和边的O-O距离比其他非共享边距离短。这些效应可以用鲍林规则来解释，并减少了阳离子之间的排斥。Ca和Ir原子的热振动具有显著的各向异性。Ca和Ir原子的热振动在朝向共享面、共享边和最短阳离子-阳离子方向的取向上受到限制。单晶实验表明，CaIrO 3晶体沿a轴沿着生长最快，并呈现棱柱或针状。这种棱柱形CaIrO 3型钙钛矿后MgSiO 3晶体的强择优取向可能在地幔剪切流下发展。
Single crystals of CaIrO3 were prepared via flux growth method. Crystal structure parameters, including the anisotropic displacement parameters, are determined based on a single-crystal X-ray diffraction experiment. The unit-cell dimensions are a = 3.147(2), b = 9.866(6), and c = 7.302(5) angstrom. The structure is a three-dimensional dense structure with small vacant spaces. The CaIrO3 structure can be described as a pseudo-one-dimensional oxide and is compared with Ca4IrO6 structure. The IrO6 octahedra are significantly distorted, in contrast to other octahedral Ir4+ compounds. The O-O distances for faces and edges shared between polyhedra are shorter than other non-shared edge distances. These effects are explained by Pauling's rules and occur to decrease the repulsion between the cations. Thermal vibrations of Ca and Ir atoms are significantly anisotropic. Thermal vibrations of Ca and Ir atoms are restricted in orientation toward the shared face, shared edges, and shortest cation-cation directions. The single-crystal experiment shows that CaIrO3 crystals grow fastest along the a axis and that they assume a prism or needle shape. Strongly preferred orientation of such prism shaped CaIrO3-type post perovskite MgSiO3 crystals may develop under the shear flow in the Earth's mantle.