  Recently, we reported the observation of superconductivity at ~0.5 K in a
La2O2M4S6-type (M: metal) layered oxychalcogenide La2O2Bi3AgS6, which is a
layered compound related to the BiS2-based superconductor system but possesses
a thicker Bi3AgS6-type conducting layer. In this study, we have developed the
La2O2Bi3AgS6-type materials by element substitutions to increase the transition
temperature (Tc) and to induce bulk nature of superconductivity. A resistivity
anomaly observed at 180 K in La2O2Bi3AgS6 was systematically suppressed by Sn
substitution for the Ag site. By the Sn substitution, Tc increased, and the
shielding volume fraction estimated from magnetization measurements also
increased. The highest Tc (= 2.3 K) and the highest shielding volume fraction
(~20%) was observed for La2O2Bi3Ag0.6Sn0.4S6. The superconducting properties
were further improved by Se substitutions for the S site. By the combinational
substitutions of Sn and Se, bulk-superconducting phase of
La2O2Bi3Ag0.6Sn0.4S5.7Se0.3 with a Tc of 3.0 K (Tconset = 3.6 K) was obtained.
