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_0.5F_0.5Bi_1−xPb_xS₂ (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. [ABSTRACT FROM AUTHOR]