Suppression of structural instability in LaOBiS2-x Se x by Se substitution

E Paris; Y Mizuguchi; T Wakita; K Terashima; T Yokoya; T Mizokawa; N L Saini

doi:10.1088/1361-648X/aae501

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

J Phys Condens Matter. 2018 Nov 14;30(45):455703. doi: 10.1088/1361-648X/aae501.

Authors

E Paris¹, Y Mizuguchi, T Wakita, K Terashima, T Yokoya, T Mizokawa, N L Saini

Affiliation

¹ Dipartimento di Fisica, Università di Roma 'La Sapienza', P. le Aldo Moro 2, 00185 Roma, Italy.

PMID: 30265246
DOI: 10.1088/1361-648X/aae501

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 BiS₂ structural instability, we have studied the local structure of LaOBiS_2-x Se _x ([Formula: see text]) using temperature dependent Bi L₃-edge extended x-ray absorption fine structure measurements. The results reveal that the local structure of the two compounds is significantly different. The BiS₂ sub-lattice is largely distorted in LaOBiS₂ (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 LaOBiS₂ (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 BiS₂ 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.