Paris E, Mizuguchi Y, Wakita T, Terashima K, Yokoya T, Mizokawa T, Saini N L
Dipartimento di Fisica, Università di Roma 'La Sapienza', P. le Aldo Moro 2, 00185 Roma, Italy.
J Phys Condens Matter. 2018 Nov 14;30(45):455703. doi: 10.1088/1361-648X/aae501.
Isovalent substitution of S by Se in LaOBiS Se has a substantial effect on its electronic structure and thermoelectric properties. To investigate the possible role of BiS structural instability, we have studied the local structure of LaOBiS Se ([Formula: see text]) using temperature dependent Bi L-edge extended x-ray absorption fine structure measurements. The results reveal that the local structure of the two compounds is significantly different. The BiS sub-lattice is largely distorted in LaOBiS (x = 0.0), with two in-plane Bi-S1 distances separated by ∼0.4 Å instead LaOBiSSe (x = 1.0) showing much smaller local disorder with two in-plane Bi-Se distances in the plane being separated by ∼0.2 Å. Temperature dependent study shows that the two Bi-S1 distances are characterized by different bond strength in LaOBiS (x = 0.0) while it is similar for the Bi-Se distances in LaOBiSSe (x = 1.0). The out of plane Bi-S2 bond is harder in LaOBiSSe indicating that the structural instability of BiS layer has large effect on the out-of-plane atomic correlations. The results suggest that the local structure of LaOBiS Se is an important factor to describe differing electronic and thermal transport of the two compounds.
在LaOBiS₂Se中用Se对等价取代S对其电子结构和热电性能有重大影响。为了研究BiS结构不稳定性的可能作用，我们使用与温度相关的Bi L边扩展X射线吸收精细结构测量研究了LaOBiS₂Se（[化学式：见原文]）的局部结构。结果表明，这两种化合物的局部结构有显著差异。在LaOBiS（x = 0.0）中，BiS亚晶格有很大畸变，两个面内Bi - S1距离相差约0.4 Å，而LaOBiSSe（x = 1.0）的局部无序要小得多，面内两个Bi - Se距离相差约0.2 Å。与温度相关的研究表明，在LaOBiS（x = 0.0）中，两个Bi - S1距离具有不同的键强，而在LaOBiSSe（x = 1.0）中，Bi - Se距离的键强相似。在LaOBiSSe中，面外Bi - S2键更强，这表明BiS层的结构不稳定性对面外原子相关性有很大影响。结果表明，LaOBiS₂Se的局部结构是描述这两种化合物不同电子和热输运的一个重要因素。
