Cd4Cu7As, The First Representative of a Fully Ordered, Orthorhombically Distorted MgCu2 Laves Phase

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• 作者：Oliver Osters ; Tom Nilges ; Michael Sch枚neich ; Peer Schmidt ; Jan Rothballer ; Florian Pielnhofer ; Richard Weihrich
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：August 6, 2012
• 年：2012
• 卷：51
• 期：15
• 页码：8119-8127
• 全文大小：576K
• 年卷期：v.51,no.15(August 6, 2012)
• ISSN：1520-510X

文摘

The ternary Laves phase Cd₄Cu₇As is the first intermetallic compound in the system Cu鈥揅d鈥揂s and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) 脜; b = 7.1251(3) 脜; c = 5.0895(4) 脜. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd₄Cu₇As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 掳C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd鈥揅u鈥揂s the cubic C15-type Laves phase Cd₄Cu_6.9(1)As_1.1(1) was structurally characterized. It crystallizes cubic in the space group Fd3m̅ with lattice parameter a = 7.0779(8) 脜. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd₄Cu₇As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB₂, Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 脜³ compared to 13 脜³ for Cu) and higher ionicity in bonding.