Local structure displacements in La1-xCex OBiSSe as a function of Ce substitution

Abstract

We have investigated the local structure of layered La1-xCexOBiSSe system by Bi L-3 -edge extended X-ray absorption fine structure (EXAFS) measurements for different Ce substitutions. Ce L-3-edge X-ray absorption spectroscopy (XAS) has been used to evaluate the Ce valence responsible for the self-doping in this system. We have found that the local distortion, determined by the separation between two Bi-Ch distances within the BiCh(2)-layer (Ch=S,Se), is quickly suppressed by Ce substitution while the axial Bi-S2 bond elongates. Ce L-3-edge XAS reveals a coexistence of Ce3+ and Ce4+ in which the Ce4+ weight decreases, an indication of a partial breaking of RE-S-Bi (RE=La/Ce) charge transfer channel with Ce substitution. the results suggest that interaction between REO spacer layer and BiCh(2) layer, dictated by the out-of-plane Bi-S2 distance, has a significant role in triggering superconductivity in the title system, with the in-plane distortion controlling the charge mobility within the BiCh(2) -layer.