Pugliese G M, Paris E, Capone F G, Stramaglia F, Wakita T, Terashima K, Yokoya T, Mizokawa T, Mizuguchi Y, Saini N L
Dipartimento di Fisica, Universitá di Roma "La Sapienza"- P. le Aldo Moro 2, 00185 Roma, Italy.
Phys Chem Chem Phys. 2020 Oct 15;22(39):22217-22225. doi: 10.1039/d0cp03974h.
We have studied the local structure of layered Eu(La,Ce)FBiS2 compounds by Bi L3-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. We find that the BiS2 sub-lattice is largely distorted in EuFBiS2, characterized by two different in-plane Bi-S1 distances. The distortion is marginally affected by partial substitutions of Ce (Eu0.5Ce0.5FBiS2) and La (Eu0.5La0.5FBiS2). The temperature dependence of the local structure distortion reveals an indication of possible charge density wave like instability in the pristine self-doped EuFBiS2 and Ce substituted Eu0.5Ce0.5FBiS2 while it is suppressed in La substituted Eu0.5La0.5FBiS2. In compounds with higher superconducting transition temperature, the axial Bi-S2 bond distance is elongated and the related bond stiffness decreased, suggesting some important role of this in the charge transfer mechanism for self-doping in the active BiS2-layer. In-plane Bi-S1 distances are generally softer than the axial Bi-S2 distance and they suffer further softening by the substitutions. The results are discussed in relation to an important role of the Bi defect chemistry driven asymmetric local environment in the physical properties of these materials.
我们通过铋L3边扩展X射线吸收精细结构（EXAFS）测量研究了层状Eu(La,Ce)FBiS2化合物的局部结构随温度的变化。我们发现，在EuFBiS2中，BiS2亚晶格发生了很大的畸变，其特征是面内Bi-S1距离有两种不同的值。Ce（Eu0.5Ce0.5FBiS2）和La（Eu0.5La0.5FBiS2）的部分替代对这种畸变的影响很小。局部结构畸变的温度依赖性表明，在原始的自掺杂EuFBiS2和Ce替代的Eu0.5Ce0.5FBiS2中可能存在类似电荷密度波的不稳定性迹象，而在La替代的Eu0.5La0.5FBiS2中这种不稳定性受到抑制。在具有较高超导转变温度的化合物中，轴向Bi-S2键距拉长，相关的键刚度降低，这表明其在活性BiS2层自掺杂的电荷转移机制中起重要作用。面内Bi-S1距离通常比轴向Bi-S2距离更易变化，并且它们会因替代而进一步变软。我们结合铋缺陷化学驱动的不对称局部环境在这些材料物理性质中的重要作用对结果进行了讨论。
