Evaluation of insulating behavior by Pb substitution and pressure-induced superconductivity in La₂O₂Bi_{3− x} Pb_{1+ x} S₆

Abstract We report synthesis, characterization, and physical properties of layered bismuth-sulfide compounds La 2 O 2 Bi 3− x Pb 1+ x S 6 . We synthesized a new La 2 O 2 Bi 3 PbS 6 compound, whose crystal structure is similar to those of the La 2 O 2 Bi 3 AgS 6 superconductor or La 2 O 2 Bi 2 Pb 2 S 6 (insulator) with a four-layer-type conducting layer. The crystal structure of La 2 O 2 Bi 3 PbS 6 is characterized in a tetragonal P 4/ nmm space group, and the lattice parameters are a = 4.084(1) Å and c = 19.71(2) Å. The obtained La 2 O 2 Bi 3 PbS 6 sample exhibits narrow gap semiconductor (metallic-like) transport behavior with an anomaly near the 160 K. A metallic-like to insulator transition has been observed through Pb substitution, with increasing x in La 2 O 2 Bi 3− x Pb 1+ x S 6 . Furthermore, we applied external pressure for x = 0 and observed pressure-induced superconductivity. The onset of superconductivity appeared at 0.93 GPa, and the highest transition temperature was 3.1 K at 2.21 GPa.