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

We examined the effect of Pb substitution in the layered superconductor LaO0.5F0.5Bi1-xPbxS2 (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.