Relationship between Resistivity Anomaly and Crystal Structure Parameters in Pb Substituted La(O,F)BiS2

We investigated the anomaly observed in the electrical resistivity in Pb substituted La(O,F)BiS2, focusing on the crystal-structure parameters. The polycrystalline LaO0.4F0.6Bi1-xPbxS2 showed that the lattice constant along the c-axis decreased at 300K at x ≥ 0.11 owing to the shrinkage of a Bi-Bi plane distance. Among them, the crystal structure at x = 0.11 transformed to one with low symmetry at 100 K. The x ≥ 0.18 samples exhibited the structure at room temperature. These samples with x ≥ 0.11 showed the anomaly at approximately 150 to 350K as well as enhanced superconducting properties compared with x < 0.11. The temperature at which the anomaly appeared increased with increasing Pb concentration. From these results, we found that the Pb substitution induced the compression of the Bi-Bi plane distance. Furthermore, this compression triggered a structural phase transition to a low-symmetry-crystal structure, resulting in anomalous electrical resistivity and enhanced superconducting properties. In addition, an increase in Pb concentration stabilized the low-symmetry-crystal structure at high temperature. These results lead to the elucidation of the relationship between the structure and superconductivity in BiCh2-based superconductors.