Cation-Poor Complex Metallic Alloys in Ba(Eu)鈥揂u鈥揂l(Ga) Systems: Identifying the Keys that Control Structural Arrangements and Atom Distributions at the Atomic Level

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• 作者：Volodymyr Smetana ; Simon Steinberg ; Yaroslav Mudryk ; Vitalij Pecharsky ; Gordon J. Miller ; Anja-Verena Mudring
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：November 2, 2015
• 年：2015
• 卷：54
• 期：21
• 页码：10296-10308
• 全文大小：709K
• ISSN：1520-510X

文摘

Four complex intermetallic compounds BaAu_6卤xGa_6卤y (x = 1, y = 0.9) (I), BaAu_6卤xAl_6卤y (x = 0.9, y = 0.6) (II), EuAu_6.2Ga_5.8 (III), and EuAu_6.1Al_5.9 (IV) have been synthesized, and their structures and homogeneity ranges have been determined by single crystal and powder X-ray diffraction. Whereas I and II originate from the NaZn₁₃-type structure (cF104鈥?12, Fm3虆c), III (tP52, P4/nbm) is derived from the tetragonal Ce₂Ni₁₇Si₉-type, and IV (oP104, Pbcm) crystallizes in a new orthorhombic structure type. Both I and II feature formally anionic networks with completely mixed site occupation by Au and triel (Tr = Al, Ga) atoms, while a successive decrease of local symmetry from the parental structures of I and II to III and, ultimately, to IV correlates with increasing separation of Au and Tr on individual crystallographic sites. Density functional theory-based calculations were employed to determine the crystallographic site preferences of Au and the respective triel element to elucidate reasons for the atom distribution (鈥渃oloring scheme鈥?. Chemical bonding analyses for two different 鈥淓uAu₆Tr₆鈥?models reveal maximization of the number of heteroatomic Au鈥揟r bonds as the driving force for atom organization. The Fermi levels fall in broad pseudogaps for both models allowing some electronic flexibility. Spin-polarized band structure calculations on the 鈥淓uAu₆Tr₆鈥?models hint to singlet ground states for europium and long-range magnetic coupling for both EuAu_6.2Ga_5.8 (III) and EuAu_6.1Al_5.9 (IV). This is substantiated by experimental evidence because both compounds show nearly identical magnetic behavior with ferromagnetic transitions at T_C = 6 K and net magnetic moments of 7.35 渭_B/f.u. at 2 K. The effective moments of 8.3 渭_B/f.u., determined from Curie鈥揥eiss fits, point to divalent oxidation states for europium in both III and IV.