  We have systematically investigated the crystal structure, magnetic
susceptibility, and electrical resistivity of the BiS2-based superconductor
LaO0.5F0.5Bi(S1-xSex)2 (x = 0 - 0.7). With expanding lattice volume by Se
substitution, bulk superconductivity was induced for x > 0.2, and the highest
Tc of 3.8 K was observed in x = 0.5 (LaO0.5F0.5BiSSe). Metallic conductivity
was observed for x > 0.3 in the resistivity measurement, whereas
semiconducting-like behavior was observed for x < 0.2. The induction of bulk
superconductivity by the partial substitution of S by Se in the LaO0.5F0.5BiS2
superconductor should be positively linked to the enhancement of metallic
conductivity.
