  Polycrystalline samples of layered pnictogen diselenide NdO0.8F0.2Sb1-xBixSe2
(x = 0 to 0.8) were successfully synthesized by solid-state reactions.
Electrical resistivity in the synthesized samples was systematically decreased
with an increase in Bi content x. Crystal structure analysis using synchrotron
X-ray diffraction suggests that insulator to metal transition upon Bi doping
correlates with anomalous change in c-axis length and/or corrugation in
conducting layer. The emergence of superconductivity under high pressure is
demonstrated using diamond anvil cell (DAC) with boron-doped diamond
electrodes, for x = 0.3 and 0.7 as the representative samples. For Sb-rich one
(x = 0.3), we observed a superconducting transition with Tconset = 5.3 K at 50
GPa, which is the first-ever report of the superconductivity in layered
SbCh2-based (Ch: chalcogen) compounds. The Tconset of x = 0.3 increased with
increasing pressure and reached 7.9 K at 70.8 GPa, followed by the gradual
decrease in Tc up to 90 GPa. For Bi-rich one (x = 0.7), a superconducting
transition with Tconset = 5.9 K was observed at 43.5 GPa, which is the almost
comparable to that of x = 0.3; besides, upper critical field (Hc2) is evaluated
to be ~10 T for x = 0.7, which is higher than that of x = 0.3 (Hc2 = 6.7 T at
50 GPa).
