Suppression of structural instability in LaOBiS_2−x Se _x by Se substitution

Abstract

Isovalent substitution of S by Se in LaOBiS 2−x Se x has a substantial effect on its electronic structure and thermoelectric properties. To investigate the possible role of BiS 2 structural instability, we have studied the local structure of LaOBiS 2−x Se x ( x = 0.0, 1.0) using temperature dependent Bi L 3 -edge extended x-ray absorption fine structure measurements. The results reveal that the local structure of the two compounds is significantly different. The BiS 2 sub-lattice is largely distorted in LaOBiS 2 (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 2 (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 2 layer has large effect on the out-of-plane atomic correlations. The results suggest that the local structure of LaOBiS 2−x Se x is an important factor to describe differing electronic and thermal transport of the two compounds.

Material Development and Physical Properties of BiS2-Based Layered Compounds

“…Basically, BiS 2 -based compounds possess a structural instability [89], probably due to the presence of lone-pair electrons of Bi [155]. In addition, on the basis of temperature dependence measurements on local disorder for LaOBiS 2-x Se x [222], the structural instability can be considered as static structural disorder. This structural instability is a key concept to understand the emergence of superconductivity, which will be explained in Sect.…”

Inhomogeneous charge distribution in a self-doped EuFBiS2 superconductor

“…The amount of self-doping is different in different regions, and is apparent from the presence and absence of the Fermi surface, therefore, the Eu-Bi charge transfer is expected to couple to the local lattice distortions [6,7] providing bistability of the metallic and nonmetallic phases. Indeed, the highly disordered nature of these materials has been revealed by the local structure measurements [10,11,13]. Here, we first assume that the observed inhomogeneous charge distribution is related to the local structure of S2 that changes the selfdoping exchange pathway of Eu-S2-Bi to inject charge in the Bi 6p x/y orbitals.…”

“…This leads the BiS 2 -based systems to be highly susceptible to external stimuli, e.g., chemical or physical pressures [8,9]. Indeed, experimental tools sensitive to the local structure have revealed a large atomic disorder [10][11][12][13], likely to be associated with the Bi defect chemistry.…”

Investigation of Superconducting Properties and Possible Nematic Superconductivity in Self‐Doped BiCh2‐Based Superconductor CeOBiS1.7Se0.3

“…In BiCh 2 ‐based compounds, the superconducting properties are strongly affected by the presence of in‐plane local disorder, which locally lowers the in‐plane structural symmetry of the Bi‐Ch1 network (see Figure b for the definition of the Ch1 site). [ 18–23 ] By increasing in‐plane CP, local structural disorder could be suppressed, and bulk superconductivity is induced in electron‐doped REOBiCh 2 . T c also increases with increasing in‐plane CP.…”