  We examined Lead (Pb) Substitution effect on a single crystal of a layered
superconductor LaO0.5F0.5BiS2. Pb concentration dependence of the lattice
constant showed slight anomaly at about 8% and 9% substitution of Pb for Bi.
These samples showed the enhancement of the superconducting transition
temperature and the superconducting volume fraction. Furthermore, these samples
showed the anomaly in the temperature dependence of the resistivity at about
150K. These results were not observed in Pb substituted NdO0.7F0.3BiS2.
Therefore, the enhancement of the superconducting properties by Pb substitution
is related to the structural instability for the pale perturbation in
LaO0.5F0.5BiS2.
