Anomalous Eu valence state and superconductivity in undoped Eu3Bi2S4F4.
Anomalous Eu valence state and superconductivity in undoped Eu3Bi2S4F4.
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DOI：
10.1021/ja508564s
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发表时间：
2014-10
影响因子：
15
通讯作者：
H. Zhai;Pan Zhang;Siqi Wu;Chaoqiong He;Z. Tang;Hao Jiang;Yun-Lei Sun;J. Bao;I. Nowik
中科院分区：
文献类型：
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作者：
H. Zhai;Pan Zhang;Siqi Wu;Chaoqiong He;Z. Tang;Hao Jiang;Yun-Lei Sun;J. Bao;I. Nowik
本文报道了一种新型的铕铋硫氟化物Eu_3Bi_2S_4F_4的合成方法。该化合物以四方晶格（空间群I4/mmm，a = 4.0771（1）μ m，c = 32.4330（6）μ m，Z = 2）结晶，其中CaF 2型Eu 3F 4层和NaCl类BiS 2双层沿晶体学c轴沿着交替堆叠。在晶体学上有两个不同的Eu位，Eu（1）和Eu（2）分别位于维科夫位置4 e和2a。基于精细结构数据的键价和计算表明，Eu（1）基本上是二价的，而Eu（2）的平均价为1.64 + 2.64（5）。这一反常的Eu价态分别由穆斯堡尔谱和磁化测量得到进一步证实和支持。Eu（3+）组分将电子贡献到主要由Bi 6px和6py态组成的导带中。因此，材料本身显示出金属导电性，并且在1.5 K下超导，而无需外部化学掺杂。
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) Å, c = 32.4330(6) Å, 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 ∼ +2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by Mössbauer and magnetization measurements. The Eu(3+) 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.