Bulk superconductivity in a four-layer-type Bi-based compound La(2)O(2)Bi(3)Ag(0.6)Sn(0.4)S(5.7)Se(0.3)

Recently, we reported the observation of superconductivity at ~0.5 K in a La(2)O(2)M(4)S(6)-type (M: metal) layered compound La(2)O(2)Bi(3)AgS(6), which is a layered system related to the BiS(2)-based superconductor system but possesses a thicker Bi(3)AgS(6)-type conducting layer. In this study, we have developed the La(2)O(2)Bi(3)AgS(6)-type materials by element substitutions to increase the transition temperature (T(c)) and to induce bulk nature of superconductivity. A resistivity anomaly observed at 180 K in La(2)O(2)Bi(3)AgS(6) was systematically suppressed by Sn substitution for the Ag site. By the Sn substitution, T(c) increased, and the shielding volume fraction estimated from magnetization measurements also increased. The highest T(c) (=2.3 K) and the highest shielding volume fraction (~20%) was observed for La(2)O(2)Bi(3)Ag(0.6)Sn(0.4)S(6). 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 La(2)O(2)Bi(3)Ag(0.6)Sn(0.4)S(5.7)Se(0.3) with a T(c) of 3.0 K (T(c)(onset) = 3.6 K) was obtained.