Ba8Ge43 revisited:: a 2a′ x 2a′ x 2a′ superstructure of the clathrate-I type with full vacancy ordering
Ba8Ge43 revisited:: a 2a′ x 2a′ x 2a′ superstructure of the clathrate-I type with full vacancy ordering
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DOI：
10.1002/zaac.200400268
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发表时间：
2004-01-01
影响因子：
1.4
通讯作者：
Grin, Y
中科院分区：
文献类型：
--
作者：
Carrillo-Cabrera, W;Budnyk, S;Grin, Y
对Ba（8）Ge（43）正方形（3）（空间群Ia（3），bard，no.230; a = 21.3123（5）埃; Z = 8; Pearson符号cI408）晶体结构的重新研究表明，锗骨架中空位（正方形）是完全有序的。这种有序的晶体结构可以被认为是理想的"Ba_8Ge_（46）"笼形物-I型结构（Pm（3）在barn上，a '= a/2）的衍生物，其中允许三个Ge空位（每个分子式单元）以具有双倍晶胞参数的立方超结构有序（正方形在24 c位置，空间群Ia（3）在barn上）。在所得到的Ge框架中，每个空位正方形被四个三键（3b）Ge-物种包围。铸态样品（在氩气气氛中冷却，未退火）的晶体中的有序性被部分破坏。对于"铸态"晶体，基于Ge在24c和24d位的部分分布，提出了一个短程模型。从电子平衡，Ba_8Ge_（43）可以被认为是一个金属Zintl相，每个分子式单元有四个过剩电子。Ba_8Ge_（43）相在770 - 810 ℃范围内是稳定的，并与Ba_6Ge_（25）和Ge平衡存在。过冷（亚稳）Ba8Ge 43分解形成一种新的类似于δ相的亚稳二元BaGe。
The reinvestigation of the crystal structure of Ba(8)Ge(43)square(3) (space group Ia (3) over bard, no. 230; a = 21.3123(5) Angstrom; Z = 8; Pearson symbol cI408) shows a full ordering of the vacancies (square) in the germanium framework. This ordered crystal structure can be considered as a derivative of an ideal "Ba8Ge46" clathrate-I type structure (Pm (3) over barn, a' = a/2) in which three Ge vacancies (per formula unit) are allowed to order in a cubic superstructure with a doubled unit cell parameter (square at the 24c site, space group Ia (3) over bard). In the resulting Ge framework, each vacancy square is surrounded by four three-bonded (3b)Ge- species. The ordering in crystals of as-cast samples (cooled in argon atmosphere, non-annealed) is partially disrupted. For the "as-cast" crystals, a short-range model is proposed based on the partial distribution of Ge on the 24c and 24d sites. From the electron balance, Ba8Ge43 can be considered as a metallic Zintl phase with four excess electrons per formula unit. The Ba8Ge43 phase is stable in the temperature range 770 - 810 degreesC and exists in equilibrium with Ba6Ge25 and Ge. By decomposition of undercooled (metastable) Ba8Ge43, a new metastable binary BaGesimilar to5 phase is formed.