  Bismuth oxysulfide Bi4O4S3, which has recently been claimed to be an exotic
superconductor (Tc = 4.5 K), was investigated by magnetic susceptibility and
electrical resistivity measurements as well as by electron probe microanalysis.
Single-phase Bi4O4S3 was successfully prepared by a high-pressure method, and
its lattice parameters and normal-state resistivity, as well as the density of
states at the Fermi level, were found to be comparable to those determined
earlier. However, the observed superconductivity was most likely
impurity-driven, strictly contradictory to the observations in ongoing
experiments. The present results indicate that the superconductivity of Bi4O4S3
does not truly reflect the bulk nature of the BiS2 layered phase, regardless of
the manner in which Bi4O4S3 is synthesized. We discuss possible superconducting
impurities.
