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首页> 外文期刊>Zeitschrift fur Naturforschung, B. A Journal of Chemical Sciences >Order and disorder of anions in tetragonal boride carbides of rare earth metals
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Order and disorder of anions in tetragonal boride carbides of rare earth metals

机译：稀土金属四方碳化硼中阴离子的有序和无序

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摘要

Compounds that feature the metal atom substructure of "La5B2C6" are known for most rare earth metals (Ln). They are characterized by two types of voids surrounded by large bicapped tetragonal antiprisms and smaller distorted octahedra, respectively. For many rare earth elements, a huge variation of lattice parameters has been observed for the corresponding compounds. A series of structure determinations has beed performed in order to elucidate the reasons for this remarkable stability range. The compounds of the earlier lanthanoids (La-Nd) exhibit broad ranges of homogeneity that are due to varying occupancy of octahedral voids which can be empty or filled by varying amounts of C atoms or C-2 groups. However, the larger voids are fully occupied with disordered C3B groups. In most cases the disorder is completely statistical with only a few exceptions. In contrast, two different phases have been observed in the case of late rare earth metals (starting from Gd). Their ranges of homogeneity are moderate, and the larger voids are fully occupied by ordered CBC entities. The difference between these two types of phases concerns the octahedral voids which contain C atoms in the case of compounds with the idealized composition Ln(5)B(2)C(5) and C-2 groups for Ln(5)B(2)C(6), respectively. Positional disorder is possible for both C atoms and C-2 groups. Therefore, no single well-defined compound is known that possesses the metal atom arrangement of "La5B2C6".
机译：大多数稀土金属（Ln）具有“ La5B2C6”金属原子亚结构特征的化合物是已知的。它们的特征是两种类型的空隙，分别被大的二尖形四边形反棱镜和较小的变形八面体围绕。对于许多稀土元素，相应化合物的晶格参数发生了巨大变化。为了阐明这种显着的稳定性范围的原因，已经进行了一系列的结构确定。较早的镧系元素（La-Nd）的化合物显示出广泛的均质性，这是由于八面体空位的占有率不同，八面体空位可以是空的，也可以被不同数量的C原子或C-2基团填充。但是，较大的空隙完全被无序的C3B基团占据。在大多数情况下，该疾病是完全统计的，只有少数例外。相反，在晚期稀土金属（从Gd开始）的情况下，观察到两个不同的相。它们的同质性范围适中，较大的空隙被有序的CBC实体完全占据。在具有理想组成Ln（5）B（2）C（5）和Ln（5）B（2）的C-2基团的化合物的情况下，这两种类型的相差涉及包含C原子的八面体空隙C（6）。 C原子和C-2基团都可能发生位置混乱。因此，没有单一的定义明确的化合物具有“ La5B2C6”的金属原子排列。

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