  The effects of pressure on the superconducting properties of a Bi-based
layered superconductor La2O2Bi3Ag0.6Sn0.4S6, which possesses a four-layer-type
conducting layer, have been studied through the electrical resistance and
magnetic susceptibility measurements. The crystal structure under pressure was
examined using synchrotron X-ray diffraction at SPring-8. In the low-pressure
regime, bulk superconductivity with a transition temperature Tc of ~ 4.5 K was
induced by pressure, which was achieved by in-plane chemical pressure effect
owing to the compression of the tetragonal structure. In the high-pressure
regime above 6.4 GPa, a structural symmetry lowering was observed, and
superconducting transitions with a Tc ~ 8 K were observed. Our results suggest
the possible commonality on the factor essential for Tc in Bi-based
superconductors with two-layer-type and four-layer-type conducting layers.
