Effect of Isovalent Substitution on the Structure and Properties of the Zintl Phase Solid Solution Eu7Cd4Sb8鈥搙Asx (2 鈮?x 鈮?5)

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• 作者：Joya Cooley ; Nasrin Kazem ; Julia V. Zaikina ; James C. Fettinger ; Susan M. Kauzlarich
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：December 21, 2015
• 年：2015
• 卷：54
• 期：24
• 页码：11767-11775
• 全文大小：546K
• ISSN：1520-510X

文摘

A novel Zintl phase structure type, Eu₇Cd₄Sb_8鈥?i>xAs_x (x = 2, 3, 4, and 5), with the general formula Eu₇Cd₄Pn₈ (Pn = mixed occupancy Sb and As), was synthesized by molten tin flux reaction. Its structure was determined using single-crystal X-ray diffraction methods. This structure type is only preserved for 2 鈮?x 鈮?5 under our experimental conditions, and efforts to synthesize samples with x < 2 or x > 5 resulted in other structure types. The mixed occupancy Sb and As can be thought of as a pseudoatom whose ideal size, in this range of Sb/As ratios, fits the structure. The title phase crystallizes in the I-centered monoclinic space group I2/m (No. 12, Z = 4) with unit cell parameters ranging as follows: a = 19.7116(17)鈥?9.4546(13) 脜, b = 4.6751(4)鈥?.6149(3) 脜, c = 24.157(2)鈥?3.871(15) 脜, and 尾 = 95.8798(1)鈥?6.016(5)掳, depending on the Sb/As ratio. The structure can be described as parallel double pentagonal tubes resulting from Cd鈥揚n and Pn鈥揚n bonding. These double pentagons are formed through corner sharing of the Cd-centered CdPn₄ tetrahedra and a Pn鈥揚n interaction from two adjacent CdPn₄ tetrahedra. This structure type is closely related to the Sr₁₁Cd₆Sb₁₂ structure type as both share the same bonding features of Pn鈥揚n bonding and double pentagonal tubes. Electron microprobe analysis confirms the composition of these new Zintl solid solution phases. The As exhibits preferential substitution on specific sites, and site specificity trends are supported by lowest energy models from theoretical calculations. Theoretical calculations also predict that Sb-rich compounds should be metallic or semimetallic and that they should become more insulating as As content increases. Members of the solid-solution order ferromagnetically between 5 and 6 K and exhibit relatively low electrical resistivity between 50 and 300 K, ranging from 鈭?.57 to 鈭?6 m惟路cm, increasing with increasing As content.