Single crystal X-ray diffraction study of the vanadate garnet Ca2NaZn2V3O12
Single crystal X-ray diffraction study of the vanadate garnet Ca2NaZn2V3O12
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DOI：
10.1016/j.materresbull.2004.03.013
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发表时间：
2004-06
影响因子：
5.4
通讯作者：
A. Nakatsuka;Y. Ikuta;A. Yoshiasa;K. Iishi
中科院分区：
文献类型：
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作者：
A. Nakatsuka;Y. Ikuta;A. Yoshiasa;K. Iishi
采用浮区（FZ）法制备了钒酸石榴石ca2nazn2v3o12单晶，并用单晶x射线衍射对其晶体结构进行了研究。由键价估算的钒酸石榴石的成键特征与硅酸盐石榴石相似，表明其晶体结构受到与硅酸盐石榴石相似的几何约束。目前钒酸石榴石具有一个显著的结构特征，即十二面体-十二面体共享边长度明显长于非共享边长度，八面体-十二面体共享边长度近似等于非共享八面体边缘长度。由于十二面体阳离子之间以及十二面体阳离子和八面体阳离子之间的弱斥力，这些由大尺寸的Ca2+和Na+带来的异常长的共享边是允许的。相比之下，石榴石结构的几何约束迫使四面体-十二面体共享边比非共享四面体边缘短得多，从而屏蔽了从原子热振动中观察到的十二面体和四面体阳离子之间的强烈排斥。在差分傅里叶图中，在十二面体和四面体阳离子之间的场中观察到被认为有助于屏蔽排斥的剩余电子密度峰。
Single crystals of the vanadate garnet Ca2NaZn2V3O12were synthesized by the floating zone (FZ) method, and its crystal structure was investigated using single-crystal X-ray diffraction. The bonding character of the present vanadate garnet estimated from bond valence is similar to that of silicate garnets, which suggests that the crystal structure is subjected to the geometric constraints similar to that of silicate garnets. The present vanadate garnet has a notable structural feature that the dodecahedral–dodecahedral shared edge length is considerably longer than the unshared dodecahedral edge length and the octahedral–dodecahedral shared edge length is approximately equal to the unshared octahedral edge length. These unusually long shared edges brought about by the large sizes of the dodecahedral cations (Ca2+and Na+) are allowed because of the weak repulsions between the dodecahedral cations and between the dodecahedral and octahedral cations. In contrast, the geometric constraints of garnet structure force the tetrahedral–dodecahedral shared edge to become considerably shorter than the unshared tetrahedral edge, and thereby the strong repulsion between the dodecahedral and tetrahedral cations, observed from the atomic thermal vibrations, is shielded. In the difference-Fourier map, the residual electron density peaks that are considered to contribute to the shielding for the repulsion are observed in the field between the dodecahedral and tetrahedral cations.