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Crystal structure of Th 2 B 2 C 3 with unique mixed B-C structural units
Acta Materialia ( IF 9.4 ) Pub Date : 2018-02-01 , DOI: 10.1016/j.actamat.2017.11.017
P.F. Rogl , R. Podloucky , H. Noël , G. Giester

X-ray single crystal data for “ThBC2” defined the crystal structure as orthorhombic (space group Pnnm; a = 1.30655(3) nm, b = 0.39757(1) nm, c = 0.36507(1) nm; RF2 = 0.0130) with the correct formula Th2B2C3. According to the new findings phase relations for the Th-B-C system at 1400 °C have been revised confirming the hitherto known thorium-boron-carbon compounds: ThBC, ThB2C and Th3B2C3. The crystal structure of Th2B2C3 as a unique structure type is characterized by a C2-branched infinite chain … B-C1-B-B-C1-B … whereby each boron atom is additionally linked to a C2-atom. Boron atoms are in a typical triangular prismatic metal coordination, C1-atoms center a bi-pyramid, Th4B2, and C2-atoms are surrounded by 5 pyramidal Th-atoms and one B-atom. Density functional theory calculations were made within the pseudopotential approach of VASP utilizing the general gradient approximation for the exchange correlation functional. Structural parameters were optimized resulting in the orthorhombic lattice parameters of a = 1.3144 nm, b = 0.3989 nm, and c = 0.3656 nm. Relativistic calculations by including spin-orbit coupling were performed for the electronic structure. Atomic volumes and charges were computed by the concept of Bader yielding the ionic charges Δq(Th) = +0.99; Δq(B) = +0.61; Δq(C1) = −1.20; Δq(C2) = −1.10. The analysis of the electronic structure shows features of chains and corresponding structural subunits with σ-like bonding. The compound appears weakly metallic with a Sommerfeld constant of γ = 3.12 mJ/(molK2) per formula unit. © 2017 Acta Materialia Inc.

中文翻译:

Th 2 B 2 C 3 的晶体结构具有独特的混合 BC 结构单元

“ThBC2”的 X 射线单晶数据将晶体结构定义为正交(空间群 Pnnm;a = 1.30655(3) nm,b = 0.39757(1) nm,c = 0.36507(1) nm;RF2 = 0.0130),其中正确的公式 Th2B2C3。根据新发现,Th-BC 系统在 1400 °C 时的相关系已得到修正,证实了迄今为止已知的钍-硼-碳化合物:ThBC、ThB2C 和 Th3B2C3。Th2B2C3 的晶体结构作为一种独特的结构类型,其特征在于 C2 支链无限链……B-C1-BB-C1-B……由此每个硼原子额外连接到一个 C2 原子。硼原子处于典型的三棱柱金属配位中,C1 原子以双金字塔、Th4B2 为中心,C2 原子被 5 个金字塔形 Th 原子和一个 B 原子包围。密度泛函理论计算是在 VASP 的赝势方法中利用交换相关泛函的一般梯度近似进行的。优化结构参数,得到 a = 1.3144 nm、b = 0.3989 nm 和 c = 0.3656 nm 的正交晶格参数。对电子结构进行了包括自旋轨道耦合的相对论计算。原子体积和电荷是通过贝德的概念计算的,产生离子电荷 Δq(Th) = +0.99;Δq(B) = +0.61;Δq(C1) = -1.20;Δq(C2) = -1.10。电子结构的分析显示了具有类σ键的链和相应结构亚单元的特征。该化合物呈弱金属性,每个分子式单位的索末菲常数为 γ = 3.12 mJ/(molK2)。© 2017 Acta Materialia Inc.
更新日期:2018-02-01
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