  We report the Se substitution effects on the crystal structure,
superconducting properties, and valence states of self-doped BiCh2-based
compound CeOBiS2-xSex. Polycrystalline CeOBiS2-xSex samples with x = 0-1.0 were
synthesized. For x = 0.4 and 0.6, bulk superconducting transitions with a large
shielding volume fraction were observed in magnetic susceptibility
measurements; the highest transition temperature (Tc) was 3.0 K for x = 0.6. A
superconductivity phase diagram of CeOBiS2-xSex was established based on Tc
estimated from the electrical resistivity and magnetization measurements. The
emergence of superconductivity in CeOBiS2-xSex was explained with two essential
parameters of in-plane chemical pressure and carrier concentration, which
systematically changed with increasing Se concentration.
