摘要：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.
