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arXiv · 1411.6903

Anomalous Eu Valence State and Superconductivity in Undoped Eu3Bi2S4F4

Hui-Fei Zhai·Pan Zhang·Si-Qi Wu·Chao-Yang He·Zhang-Tu Tang·Hao Jiang·Yun-Lei Sun·Jin-Ke Bao·I. Nowik·I. Felner·Yue-Wu Zeng·Yu-Ke Li·Xiao-Feng Xu·Qian Tao·Zhu-An Xu·Guang-Han Cao
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Abstract

We have synthesized a novel europium bismuth sulfofluoride, Eu3Bi2S4F4, by solid-state reactions in sealed evacuated quartz ampoules. The compound crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) A, c = 32.4330(6) A, 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, whilst Eu(2) has an average valence of +2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by Mossbauer and magnetization measurements. The Eu3+ components donate electrons into the conduction bands that are mainly composed of Bi- 6px and 6py states. Consequently, the material itself shows metallic conduction, and superconducts at 1.5 K without extrinsic chemical doping.

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Hui-Fei Zhai, Pan Zhang, Si-Qi Wu, Chao-Yang He, Zhang-Tu Tang, Hao Jiang, Yun-Lei Sun, Jin-Ke Bao, I. Nowik, I. Felner, Yue-Wu Zeng, Yu-Ke Li, Xiao-Feng Xu, Qian Tao, Zhu-An Xu, Guang-Han Cao. 2014-11-25. Anomalous Eu Valence State and Superconductivity in Undoped Eu3Bi2S4F4. https://doi.org/10.1021/ja508564s

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