Anomalous Eu Valence State and Superconductivity in Undoped Eu3Bi2S4F4

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• 作者：Hui-Fei Zhai ; Pan Zhang ; Si-Qi Wu ; Chao-Yang He ; Zhang-Tu Tang ; Hao Jiang ; Yun-Lei Sun ; Jin-Ke Bao ; Israel Nowik ; Israel Felner ; Yue-Wu Zeng ; Yu-Ke Li ; Xiao-Feng Xu ; Qian Tao ; Zhu-An Xu ; Guang-Han Cao
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：October 29, 2014
• 年：2014
• 卷：136
• 期：43
• 页码：15386-15393
• 全文大小：470K
• ISSN：1520-5126

文摘

We have synthesized a novel europium bismuth sulfofluoride, Eu₃Bi₂S₄F₄, by solid-state reactions in sealed evacuated quartz ampules. The compound crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) 脜, c = 32.4330(6) 脜, and Z = 2), in which CaF₂-type Eu₃F₄ layers and NaCl-like BiS₂ bilayers stack alternately along the crystallographic c axis. There are two crystallographically distinct Eu sites, Eu(1) and Eu(2) at the Wyckoff positions 4e and 2a, respectively. Our bond valence sum calculation, based on the refined structural data, indicates that Eu(1) is essentially divalent, while Eu(2) has an average valence of 鈭尖€?2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by M枚ssbauer and magnetization measurements. The Eu³⁺ components donate electrons into the conduction bands that are mainly composed of Bi 6p_x and 6p_y states. Consequently, the material itself shows metallic conduction and superconducts at 1.5 K without extrinsic chemical doping.