  We report the effects of Ce substitution on structural, electronic, and
magnetic properties of layered bismuth-chalcogenide La1-xCexOBiSSe (x = 0-0.9),
which are newly obtained in this study. Metallic conductivity was observed for
x > 0.1 because of electron carriers induced by mixed valence of Ce ions, as
revealed by bond valence sum calculation and magnetization measurements. Zero
resistivity and clear diamagnetic susceptibility were obtained for x = 0.2-0.6,
indicating the emergence of bulk superconductivity in these compounds.
Dome-shaped superconductivity phase diagram with the highest transition
temperature (Tc) of 3.1 K, which is slightly lower than that of F-doped
LaOBiSSe (Tc = 3.7 K), was established. The present study clearly shows that
the mixed valence of Ce ions can be utilized as an alternative approach for
electron-doping in layered bismuth-chalcogenides to induce superconductivity.
