Pb Substitution Effects on Lattice and Electronic System of the BiS₂-based Superconductors La(OF)BiS₂

We examined the effect of Pb substitution in the layered superconductor LaO 0.5 F 0.5 Bi 1-x Pb x S 2 (x = 0∼0.15)through the measurements of the resistivity, thermal expansion, specific heat, and Seebeck coefficient.These transport and thermal properties show anomalies at certain temperatures (T*) for x≥0.08.The large thermal expansion anomalies, specific heat anomalies, and the existence of hystereses in the above measurements indicate a first-order structural phase transition at T*. Additionally, the Seebeck coefficient indicates that the anomalies at T* are related not only to the lattice system, but also to the electronic system.Superconductivity is not observed above 2 K at x=0.08, which is around the phase boundary where T* vanishes.The suppression of superconductivity around the structural phase boundary suggests a close relationship between the lattice and superconductivity.