Intrinsic non-stoichiometry and anomalous transport properties of layered oxysulfide LaOPbBiS3

Abstract

We report on the intrinsic non-stoichiometry and the influence of fluorine doping on the low temperature transport properties of layered oxysulfide LaOPbBiS₃. From X-ray diffraction coupled to electron microscopy studies, we show that this compound is intrinsically non-stoichiometric, with a partial substitution of Pb by excess Bi leading to electron self-doping. Upon fluorine doping, a monotonic decrease of the lattice parameter shows that fluorine can be introduced on the oxygen site up to at least 12.5%. Although this doping does not lead to simple electron doping, it induces a marked anomaly of the low temperature electrical properties, with a bump of the electrical resistivity coupled to a peak of the Seebeck coefficient, indicative of a non-trivial electronic structure. Our results show that the study of the defect chemistry of BiS₂-based layered oxysulfides would be of primary importance in order to understand and control their electrical properties.