Journal of the American Chemical Society, Vol.134, No.40, 16504-16507, 2012
Bulk Superconductivity in Bismuth Oxysulfide Bi4O4S3
A very recent report on the observation of superconductivity in Bi4O4S3 [Mizuguchi, Y.; et al. http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi4O4S3 at 500 degrees C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi4O4S3 was contaminated with small amounts of Bi2S3 and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) angstrom and c = 41.3520(1) angstrom. Both AC and DC magnetization measurements confirmed that Bi4O4S3 is a bulk superconductor with a superconducting transition temperature (T-c) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H-cl) at 2 K for the new superconductor was found to be similar to 15 Oe. Magnetotransport measurements showed a broadening of the resistivity (rho) and a decrease in T-c (rho = 0) with increasing magnetic field. The extrapolated upper critical field H-c2(0) was similar to 31 kOe with a corresponding Ginzburg-Landau coherence length of similar to 100 angstrom. In the normal state, the rho similar to T-2 dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi4O4S3. On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi4O4S3.